qquicklistview.cpp

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// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
// Qt-Security score:significant reason:default
 
#include "qquicklistview_p.h"
#include "qquickitemview_p_p.h"
#include "qquickflickablebehavior_p.h"
 
#include <private/qqmlobjectmodel_p.h>
#include <QtQml/qqmlexpression.h>
#include <QtQml/qqmlengine.h>
#include <QtQml/qqmlinfo.h>
#include <QtGui/qevent.h>
#include <QtCore/qcoreapplication.h>
#include <QtCore/qmath.h>
 
#include <private/qquicksmoothedanimation_p_p.h>
#include <private/qqmlcomponent_p.h>
 
QT_BEGIN_NAMESPACE
 
#ifndef QML_FLICK_SNAPONETHRESHOLD
#define QML_FLICK_SNAPONETHRESHOLD 30
#endif
 
Q_STATIC_LOGGING_CATEGORY(lcEvents, "qt.quick.listview.events")
 
class FxListItemSG;
 
class QQuickListViewPrivate : public QQuickItemViewPrivate
{
public:
    Q_DECLARE_PUBLIC(QQuickListView)
    static QQuickListViewPrivate* get(QQuickListView *item) { return item->d_func(); }
 
    Qt::Orientation layoutOrientation() const override;
    bool isContentFlowReversed() const override;
    bool isRightToLeft() const;
    bool isBottomToTop() const;
 
    qreal positionAt(int index) const override;
    qreal endPositionAt(int index) const override;
    qreal originPosition() const override;
    qreal lastPosition() const override;
 
    FxViewItem *itemBefore(int modelIndex) const;
    QString sectionAt(int modelIndex);
    qreal snapPosAt(qreal pos);
    FxViewItem *snapItemAt(qreal pos);
 
    void init() override;
    void clear(bool onDestruction) override;
 
    bool addVisibleItems(qreal fillFrom, qreal fillTo, qreal bufferFrom, qreal bufferTo, bool doBuffer) override;
    bool removeNonVisibleItems(qreal bufferFrom, qreal bufferTo) override;
    void visibleItemsChanged() override;
 
    void removeItem(FxViewItem *item);
 
    FxViewItem *newViewItem(int index, QQuickItem *item) override;
    void initializeViewItem(FxViewItem *item) override;
    bool releaseItem(FxViewItem *item, QQmlInstanceModel::ReusableFlag reusableFlag) override;
    void repositionItemAt(FxViewItem *item, int index, qreal sizeBuffer) override;
    void repositionPackageItemAt(QQuickItem *item, int index) override;
    void resetFirstItemPosition(qreal pos = 0.0) override;
    void adjustFirstItem(qreal forwards, qreal backwards, int) override;
    void updateSizeChangesBeforeVisiblePos(FxViewItem *item, ChangeResult *removeResult) override;
 
    void createHighlight(bool onDestruction = false) override;
    void updateHighlight() override;
    void resetHighlightPosition() override;
    bool movingFromHighlight() override;
 
    void setPosition(qreal pos) override;
    void layoutVisibleItems(int fromModelIndex = 0) override;
 
    bool applyInsertionChange(const QQmlChangeSet::Change &insert, ChangeResult *changeResult, QList<FxViewItem *> *addedItems, QList<MovedItem> *movingIntoView) override;
#if QT_CONFIG(quick_viewtransitions)
    void translateAndTransitionItemsAfter(int afterIndex, const ChangeResult &insertionResult, const ChangeResult &removalResult) override;
#endif
 
    void updateSectionCriteria() override;
    void updateSections() override;
    QQuickItem *getSectionItem(const QString &section);
    void releaseSectionItem(QQuickItem *item);
    void releaseSectionItems();
    void updateInlineSection(FxListItemSG *);
    void updateCurrentSection();
    void updateStickySections();
    void updateSectionFocusOrder();
 
    qreal headerSize() const override;
    qreal footerSize() const override;
    bool showHeaderForIndex(int index) const override;
    bool showFooterForIndex(int index) const override;
    void updateHeader() override;
    void updateFooter() override;
    bool hasStickyHeader() const override;
    bool hasStickyFooter() const override;
 
    void initializeComponentItem(QQuickItem *item) const override;
 
    void changedVisibleIndex(int newIndex) override;
    void initializeCurrentItem() override;
 
    void updateAverage();
 
    void itemGeometryChanged(QQuickItem *item, QQuickGeometryChange change, const QRectF &oldGeometry) override;
    void fixupPosition() override;
    void fixup(AxisData &data, qreal minExtent, qreal maxExtent) override;
    bool flick(QQuickItemViewPrivate::AxisData &data, qreal minExtent, qreal maxExtent, qreal vSize,
               QQuickTimeLineCallback::Callback fixupCallback, QEvent::Type eventType, qreal velocity) override;
 
    QQuickItemViewAttached *getAttachedObject(const QObject *object) const override;
 
    void fixupHeader();
    void fixupHeaderCompleted();
 
    bool wantsPointerEvent(const QPointerEvent *event) override;
 
    QQuickListView::Orientation orient;
    qreal visiblePos;
    qreal averageSize;
    qreal spacing;
    QQuickListView::SnapMode snapMode;
 
    QQuickListView::HeaderPositioning headerPositioning;
    QQuickListView::FooterPositioning footerPositioning;
 
    std::unique_ptr<QSmoothedAnimation> highlightPosAnimator;
    std::unique_ptr<QSmoothedAnimation> highlightWidthAnimator;
    std::unique_ptr<QSmoothedAnimation> highlightHeightAnimator;
    qreal highlightMoveVelocity;
    qreal highlightResizeVelocity;
    int highlightResizeDuration;
 
    QQuickViewSection *sectionCriteria;
    QString currentSection;
    static const int sectionCacheSize = 5;
    QQuickItem *sectionCache[sectionCacheSize];
    QQuickItem *currentSectionItem;
    QString currentStickySection;
    QQuickItem *nextSectionItem;
    QString nextStickySection;
    QString lastVisibleSection;
    QString nextSection;
 
    qreal overshootDist;
 
    qreal desiredViewportPosition;
    qreal fixupHeaderPosition;
    bool headerNeedsSeparateFixup : 1;
    bool desiredHeaderVisible : 1;
 
    bool correctFlick : 1;
    bool inFlickCorrection : 1;
    bool wantedMousePress : 1;
 
    int snapResizeTargetIndex = -1;
 
    QQuickListViewPrivate()
        : orient(QQuickListView::Vertical)
        , visiblePos(0)
        , averageSize(100.0), spacing(0.0)
        , snapMode(QQuickListView::NoSnap)
        , headerPositioning(QQuickListView::InlineHeader)
        , footerPositioning(QQuickListView::InlineFooter)
        , highlightPosAnimator(nullptr), highlightWidthAnimator(nullptr), highlightHeightAnimator(nullptr)
        , highlightMoveVelocity(400), highlightResizeVelocity(400), highlightResizeDuration(-1)
        , sectionCriteria(nullptr), currentSectionItem(nullptr), nextSectionItem(nullptr)
        , overshootDist(0.0), desiredViewportPosition(0.0), fixupHeaderPosition(0.0)
        , headerNeedsSeparateFixup(false), desiredHeaderVisible(false)
        , correctFlick(false), inFlickCorrection(false), wantedMousePress(false)
    {
        highlightMoveDuration = -1; //override default value set in base class
    }
 
    friend class QQuickViewSection;
 
    static void setSectionHelper(QQmlContext *context, QQuickItem *sectionItem, const QString &section);
};
 
//----------------------------------------------------------------------------
 
QQuickViewSection::QQuickViewSection(QQuickListView *parent)
    : QObject(parent), m_criteria(FullString), m_delegate(nullptr), m_labelPositioning(InlineLabels)
    , m_view(parent ? QQuickListViewPrivate::get(parent) : nullptr)
{
}
 
void QQuickViewSection::setProperty(const QString &property)
{
    if (property != m_property) {
        m_property = property;
        emit propertyChanged();
        // notify view that the contents of the sections must be recalculated
        m_view->updateSectionCriteria();
    }
}
 
void QQuickViewSection::setCriteria(QQuickViewSection::SectionCriteria criteria)
{
    if (criteria != m_criteria) {
        m_criteria = criteria;
        emit criteriaChanged();
        // notify view that the contents of the sections must be recalculated
        m_view->updateSectionCriteria();
    }
}
 
void QQuickViewSection::setDelegate(QQmlComponent *delegate)
{
    if (delegate != m_delegate) {
        if (m_delegate)
            m_view->releaseSectionItems();
        m_delegate = delegate;
        emit delegateChanged();
        m_view->forceLayoutPolish();
    }
}
 
QString QQuickViewSection::sectionString(const QString &value)
{
    if (m_criteria == FirstCharacter)
        return value.isEmpty() ? QString() : value.at(0);
    else
        return value;
}
 
void QQuickViewSection::setLabelPositioning(int l)
{
    if (m_labelPositioning != l) {
        m_labelPositioning = l;
        emit labelPositioningChanged();
        m_view->forceLayoutPolish();
    }
}
 
//----------------------------------------------------------------------------
 
class FxListItemSG : public FxViewItem
{
public:
    FxListItemSG(QQuickItem *i, QQuickListView *v, bool own) : FxViewItem(i, v, own, static_cast<QQuickItemViewAttached*>(qmlAttachedPropertiesObject<QQuickListView>(i))), view(v)
    {
    }
 
    inline QQuickItem *section() const {
        return item && attached ? static_cast<QQuickListViewAttached*>(attached)->m_sectionItem : nullptr;
    }
    void setSection(QQuickItem *s) {
        static_cast<QQuickListViewAttached*>(attached)->m_sectionItem = s;
    }
 
    qreal position() const override {
        if (section()) {
            if (view->orientation() == QQuickListView::Vertical)
                return (view->verticalLayoutDirection() == QQuickItemView::BottomToTop ? -section()->height()-section()->y() : section()->y());
            else
                return (view->effectiveLayoutDirection() == Qt::RightToLeft ? -section()->width()-section()->x() : section()->x());
        } else {
            return itemPosition();
        }
    }
    qreal itemPosition() const {
        if (view->orientation() == QQuickListView::Vertical)
            return (view->verticalLayoutDirection() == QQuickItemView::BottomToTop ? -itemHeight()-itemY() : itemY());
        else
            return (view->effectiveLayoutDirection() == Qt::RightToLeft ? -itemWidth()-itemX() : itemX());
    }
    qreal size() const override {
        if (section())
            return (view->orientation() == QQuickListView::Vertical ? itemHeight()+section()->height() : itemWidth()+section()->width());
        else
            return (view->orientation() == QQuickListView::Vertical ? itemHeight() : itemWidth());
    }
    qreal itemSize() const {
        return (view->orientation() == QQuickListView::Vertical ? itemHeight() : itemWidth());
    }
    qreal sectionSize() const override {
        if (section())
            return (view->orientation() == QQuickListView::Vertical ? section()->height() : section()->width());
        return 0.0;
    }
    qreal endPosition() const override {
        if (view->orientation() == QQuickListView::Vertical) {
            return (view->verticalLayoutDirection() == QQuickItemView::BottomToTop
                    ? -itemY()
                    : itemY() + itemHeight());
        } else {
            return (view->effectiveLayoutDirection() == Qt::RightToLeft
                    ? -itemX()
                    : itemX() + itemWidth());
        }
    }
 
    void setPosition(qreal pos, bool immediate = false, bool resetInactiveAxis = true) {
        // position the section immediately even if there is a transition
        if (section()) {
            if (view->orientation() == QQuickListView::Vertical) {
                if (view->verticalLayoutDirection() == QQuickItemView::BottomToTop)
                    section()->setY(-section()->height()-pos);
                else
                    section()->setY(pos);
            } else {
                if (view->effectiveLayoutDirection() == Qt::RightToLeft)
                    section()->setX(-section()->width()-pos);
                else
                    section()->setX(pos);
            }
        }
        moveTo(pointForPosition(pos, resetInactiveAxis), immediate);
    }
 
    void setSize(qreal size) {
        if (view->orientation() == QQuickListView::Vertical)
            item->setHeight(size);
        else
            item->setWidth(size);
    }
    bool contains(qreal x, qreal y) const override {
        return (x >= itemX() && x < itemX() + itemWidth() &&
                y >= itemY() && y < itemY() + itemHeight());
    }
 
    QQuickListView *view;
 
private:
    QPointF pointForPosition(qreal pos, bool resetInactiveAxis) const {
        if (view->orientation() == QQuickListView::Vertical) {
            if (view->verticalLayoutDirection() == QQuickItemView::BottomToTop) {
                if (section())
                    pos += section()->height();
                return QPointF(resetInactiveAxis ? 0 : itemX(), -itemHeight() - pos);
            } else {
                if (section())
                    pos += section()->height();
                return QPointF(resetInactiveAxis ? 0 : itemX(), pos);
            }
        } else {
            if (view->effectiveLayoutDirection() == Qt::RightToLeft) {
                if (section())
                    pos += section()->width();
                return QPointF(-itemWidth() - pos, resetInactiveAxis ? 0 : itemY());
            } else {
                if (section())
                    pos += section()->width();
                return QPointF(pos, resetInactiveAxis ? 0 : itemY());
            }
        }
    }
};
 
/*! \internal
    \brief A helper class for iterating over a model that might change
 
    When populating the ListView from a model under normal
    circumstances, we would iterate over the range of model indices
    correspondning to the visual range, and basically call
    createItem(index++) in order to create each item.
 
    This will also emit Component.onCompleted() for each item, which
    might do some weird things...  For instance, it might remove itself
    from the model, and this might change model count and the indices
    of the other subsequent entries in the model.
 
    This class takes such changes to the model into consideration while
    iterating, and will adjust the iterator index and keep track of
    whether the iterator has reached the end of the range.
 
    It keeps track of changes to the model by connecting to
    QQmlInstanceModel::modelUpdated() from its constructor.
    When destroyed, it will automatically disconnect. You can
    explicitly disconnect earlier by calling \fn disconnect().
*/
class MutableModelIterator {
public:
    MutableModelIterator(QQmlInstanceModel *model, int iBegin, int iEnd)
        : removedAtIndex(false)
        , backwards(iEnd < iBegin)
    {
        conn = QObject::connect(model, &QQmlInstanceModel::modelUpdated, model,
                [&] (const QQmlChangeSet &changeSet, bool /*reset*/)
        {
            for (const QQmlChangeSet::Change &rem : changeSet.removes()) {
                idxEnd -= rem.count;
                if (rem.start() <= index) {
                    if (index < rem.start() + rem.count) {
                        // The removed range covers us. Collapse onto its start
                        // rather than subtracting the whole count, which would
                        // move the index before the beginning of the model.
                        removedAtIndex = true;
                        index = rem.start();
                    } else {
                        index -= rem.count;
                    }
                }
            }
            for (const QQmlChangeSet::Change &ins : changeSet.inserts()) {
                idxEnd += ins.count;
                if (ins.start() <= index)
                    index += ins.count;
            }
        }
        );
        index = iBegin;
        idxEnd = iEnd;
    }
 
    bool hasNext() const {
        return backwards ? index > idxEnd : index < idxEnd;
    }
 
    void next() { index += (backwards ? -1 : +1); }
 
    ~MutableModelIterator()
    {
        disconnect();
    }
 
    void disconnect()
    {
        if (conn) {
            QObject::disconnect(conn);
            conn = QMetaObject::Connection();   // set to nullptr
        }
    }
    int index = 0;
    int idxEnd;
    unsigned removedAtIndex : 1;
    unsigned backwards : 1;
private:
    QMetaObject::Connection conn;
};
 
 
//----------------------------------------------------------------------------
 
bool QQuickListViewPrivate::isContentFlowReversed() const
{
    return isRightToLeft() || isBottomToTop();
}
 
Qt::Orientation QQuickListViewPrivate::layoutOrientation() const
{
    return static_cast<Qt::Orientation>(orient);
}
 
bool QQuickListViewPrivate::isRightToLeft() const
{
    Q_Q(const QQuickListView);
    return orient == QQuickListView::Horizontal && q->effectiveLayoutDirection() == Qt::RightToLeft;
}
 
bool QQuickListViewPrivate::isBottomToTop() const
{
    return orient == QQuickListView::Vertical && verticalLayoutDirection == QQuickItemView::BottomToTop;
}
 
// Returns the item before modelIndex, if created.
// May return an item marked for removal.
FxViewItem *QQuickListViewPrivate::itemBefore(int modelIndex) const
{
    if (modelIndex < visibleIndex)
        return nullptr;
    int idx = 1;
    int lastIndex = -1;
    while (idx < visibleItems.size()) {
        FxViewItem *item = visibleItems.at(idx);
        if (item->index != -1)
            lastIndex = item->index;
        if (item->index == modelIndex)
            return visibleItems.at(idx-1);
        ++idx;
    }
    if (lastIndex == modelIndex-1)
        return visibleItems.constLast();
    return nullptr;
}
 
void QQuickListViewPrivate::setPosition(qreal pos)
{
    Q_Q(QQuickListView);
    if (orient == QQuickListView::Vertical) {
        if (isBottomToTop())
            q->QQuickFlickable::setContentY(-pos-size());
        else
            q->QQuickFlickable::setContentY(pos);
    } else {
        if (isRightToLeft())
            q->QQuickFlickable::setContentX(-pos-size());
        else
            q->QQuickFlickable::setContentX(pos);
    }
}
 
qreal QQuickListViewPrivate::originPosition() const
{
    qreal pos = 0;
    if (!visibleItems.isEmpty()) {
        pos = (*visibleItems.constBegin())->position();
        if (visibleIndex > 0)
            pos -= visibleIndex * (averageSize + spacing);
    }
    return pos;
}
 
qreal QQuickListViewPrivate::lastPosition() const
{
    qreal pos = 0;
    if (!visibleItems.isEmpty()) {
        int invisibleCount = INT_MIN;
        int delayRemovedCount = 0;
        for (int i = visibleItems.size()-1; i >= 0; --i) {
            FxViewItem *item = visibleItems.at(i);
            if (item->index != -1) {
                // Find the invisible count after the last visible item with known index
                invisibleCount = model->count() - (item->index + 1 + delayRemovedCount);
                break;
            } else if (item->attached->delayRemove()) {
                ++delayRemovedCount;
            }
        }
        if (invisibleCount == INT_MIN) {
            // All visible items are in delayRemove state
            invisibleCount = model->count();
        }
        pos = (*(visibleItems.constEnd() - 1))->endPosition();
        if (invisibleCount > 0)
            pos += invisibleCount * (averageSize + spacing);
    } else if (model && model->count()) {
        pos = (model->count() * averageSize + (model->count()-1) * spacing);
    }
    return pos;
}
 
qreal QQuickListViewPrivate::positionAt(int modelIndex) const
{
    if (FxViewItem *item = visibleItem(modelIndex)) {
        return item->position();
    }
    if (!visibleItems.isEmpty()) {
        if (modelIndex < visibleIndex) {
            int count = visibleIndex - modelIndex;
            qreal cs = 0;
            if (modelIndex == currentIndex && currentItem) {
                cs = currentItem->size() + spacing;
                --count;
            }
            return (*visibleItems.constBegin())->position() - count * (averageSize + spacing) - cs;
        } else {
            int count = modelIndex - findLastVisibleIndex(visibleIndex) - 1;
            return (*(visibleItems.constEnd() - 1))->endPosition() + spacing + count * (averageSize + spacing);
        }
    }
    return 0;
}
 
qreal QQuickListViewPrivate::endPositionAt(int modelIndex) const
{
    if (FxViewItem *item = visibleItem(modelIndex))
        return item->endPosition();
    if (!visibleItems.isEmpty()) {
        if (modelIndex < visibleIndex) {
            int count = visibleIndex - modelIndex;
            return (*visibleItems.constBegin())->position() - (count - 1) * (averageSize + spacing) - spacing;
        } else {
            int count = modelIndex - findLastVisibleIndex(visibleIndex) - 1;
            return (*(visibleItems.constEnd() - 1))->endPosition() + count * (averageSize + spacing);
        }
    }
    return 0;
}
 
QString QQuickListViewPrivate::sectionAt(int modelIndex)
{
    if (FxViewItem *item = visibleItem(modelIndex))
        return item->attached->section();
 
    QString section;
    if (sectionCriteria && modelIndex >= 0 && modelIndex < itemCount) {
        QString propValue = model->stringValue(modelIndex, sectionCriteria->property());
        section = sectionCriteria->sectionString(propValue);
    }
 
    return section;
}
 
qreal QQuickListViewPrivate::snapPosAt(qreal pos)
{
    if (FxListItemSG *snapItem = static_cast<FxListItemSG*>(snapItemAt(pos)))
        return snapItem->itemPosition();
    if (visibleItems.size()) {
        qreal firstPos = (*visibleItems.constBegin())->position();
        qreal endPos = (*(visibleItems.constEnd() - 1))->position();
        if (pos < firstPos) {
            return firstPos - qRound((firstPos - pos) / averageSize) * averageSize;
        } else if (pos > endPos)
            return endPos + qRound((pos - endPos) / averageSize) * averageSize;
    }
    return qRound((pos - originPosition()) / averageSize) * averageSize + originPosition();
}
 
FxViewItem *QQuickListViewPrivate::snapItemAt(qreal pos)
{
    const qreal velocity = orient == QQuickListView::Vertical ? vData.velocity : hData.velocity;
    FxViewItem *snapItem = nullptr;
    FxViewItem *prevItem = nullptr;
    qreal prevItemSize = 0;
    for (FxViewItem *item : std::as_const(visibleItems)) {
        if (item->index == -1)
            continue;
 
        const FxListItemSG *listItem = static_cast<FxListItemSG *>(item);
        qreal itemTop = listItem->position();
        qreal itemSize = listItem->size();
        if (highlight && itemTop >= pos && listItem->endPosition() <= pos + highlight->size())
            return item;
 
        if (listItem->section() && velocity > 0) {
            if (itemTop + listItem->sectionSize() / 2 >= pos && itemTop - prevItemSize / 2 < pos)
                snapItem = prevItem;
            itemTop = listItem->itemPosition();
            itemSize = listItem->itemSize();
        }
 
        // Middle of item and spacing (i.e. the middle of the distance between this item and the next
        qreal halfwayToNextItem = itemTop + (itemSize+spacing) / 2;
        qreal halfwayToPrevItem = itemTop - (prevItemSize+spacing) / 2;
        if (halfwayToNextItem >= pos && halfwayToPrevItem < pos)
            snapItem = item;
 
        prevItemSize = listItem->itemSize();
        prevItem = item;
    }
    return snapItem;
}
 
void QQuickListViewPrivate::changedVisibleIndex(int newIndex)
{
    visiblePos = positionAt(newIndex);
    visibleIndex = newIndex;
}
 
void QQuickListViewPrivate::init()
{
    QQuickItemViewPrivate::init();
    ::memset(sectionCache, 0, sizeof(QQuickItem*) * sectionCacheSize);
}
 
void QQuickListViewPrivate::clear(bool onDestruction)
{
    for (int i = 0; i < sectionCacheSize; ++i) {
        delete sectionCache[i];
        sectionCache[i] = nullptr;
    }
    visiblePos = 0;
    releaseSectionItem(currentSectionItem);
    currentSectionItem = nullptr;
    releaseSectionItem(nextSectionItem);
    nextSectionItem = nullptr;
    lastVisibleSection = QString();
    QQuickItemViewPrivate::clear(onDestruction);
}
 
FxViewItem *QQuickListViewPrivate::newViewItem(int modelIndex, QQuickItem *item)
{
    Q_Q(QQuickListView);
 
    FxListItemSG *listItem = new FxListItemSG(item, q, false);
    listItem->index = modelIndex;
 
    // initialise attached properties
    if (sectionCriteria) {
        QString propValue = model->stringValue(modelIndex, sectionCriteria->property());
        QString section = sectionCriteria->sectionString(propValue);
        QString prevSection;
        QString nextSection;
        if (modelIndex > 0) {
            if (FxViewItem *item = itemBefore(modelIndex))
                prevSection = item->attached->section();
            else
                prevSection = sectionAt(modelIndex-1);
        }
        if (modelIndex < model->count()-1) {
            nextSection = sectionAt(modelIndex+1);
        }
        listItem->attached->setSections(prevSection, section, nextSection);
    }
 
    return listItem;
}
 
void QQuickListViewPrivate::initializeViewItem(FxViewItem *item)
{
    QQuickItemViewPrivate::initializeViewItem(item);
 
    // need to track current items that are animating
    item->trackGeometry(true);
 
    if (sectionCriteria && sectionCriteria->delegate()) {
        auto *listItem = static_cast<FxListItemSG*>(item);
        // QTBUG-146169: Try to update if exists. Due to a timing issue, an item may already have
        // a (stale) section item it no longer needs
        if (QString::compare(item->attached->m_prevSection, item->attached->m_section, Qt::CaseInsensitive)
                || listItem->section())
            updateInlineSection(listItem);
    }
}
 
bool QQuickListViewPrivate::releaseItem(FxViewItem *item, QQmlInstanceModel::ReusableFlag reusableFlag)
{
    if (!item || !model)
        return QQuickItemViewPrivate::releaseItem(item, reusableFlag);
 
    QPointer<QQuickItem> it = item->item;
    QQuickListViewAttached *att = static_cast<QQuickListViewAttached*>(item->attached);
 
    bool released = QQuickItemViewPrivate::releaseItem(item, reusableFlag);
    if (released && it && att && att->m_sectionItem) {
        QQuickItemPrivate::get(att->m_sectionItem)->removeItemChangeListener(this, QQuickItemPrivate::Geometry);
 
        // We hold no more references to this item
        int i = 0;
        do {
            if (!sectionCache[i]) {
                sectionCache[i] = att->m_sectionItem;
                sectionCache[i]->setVisible(false);
                att->m_sectionItem = nullptr;
                break;
            }
            ++i;
        } while (i < sectionCacheSize);
        delete att->m_sectionItem;
        att->m_sectionItem = nullptr;
    }
 
    return released;
}
 
bool QQuickListViewPrivate::addVisibleItems(qreal fillFrom, qreal fillTo, qreal bufferFrom, qreal bufferTo, bool doBuffer)
{
    qreal itemEnd = visiblePos;
    if (visibleItems.size()) {
        visiblePos = (*visibleItems.constBegin())->position();
        itemEnd = (*(visibleItems.constEnd() - 1))->endPosition() + spacing;
    }
 
    int modelIndex = findLastVisibleIndex();
    bool haveValidItems = modelIndex >= 0;
    modelIndex = modelIndex < 0 ? visibleIndex : modelIndex + 1;
 
    if (haveValidItems && (bufferFrom > itemEnd+averageSize+spacing
        || bufferTo < visiblePos - averageSize - spacing)) {
        // We've jumped more than a page.  Estimate which items are now
        // visible and fill from there.
        int count = (fillFrom - itemEnd) / (averageSize + spacing);
        int newModelIdx = qBound(0, modelIndex + count, model->count());
        count = newModelIdx - modelIndex;
        if (count) {
            releaseVisibleItems(reusableFlag);
            modelIndex = newModelIdx;
            visibleIndex = modelIndex;
            visiblePos = itemEnd + count * (averageSize + spacing);
            itemEnd = visiblePos;
        }
    }
 
    QQmlIncubator::IncubationMode incubationMode = doBuffer ? QQmlIncubator::Asynchronous : QQmlIncubator::AsynchronousIfNested;
 
    bool changed = false;
    FxListItemSG *item = nullptr;
    qreal pos = itemEnd;
    while (modelIndex < model->count() && pos <= fillTo) {
        if (!(item = static_cast<FxListItemSG*>(createItem(modelIndex, incubationMode))))
            break;
        qCDebug(lcItemViewDelegateLifecycle) << "refill: append item" << modelIndex << "pos" << pos << "buffer" << doBuffer << "item" << (QObject *)(item->item);
#if QT_CONFIG(quick_viewtransitions)
        if (!transitioner || !transitioner->canTransition(QQuickItemViewTransitioner::PopulateTransition, true)) // pos will be set by layoutVisibleItems()
#endif
            item->setPosition(pos, true);
        if (item->item)
            QQuickItemPrivate::get(item->item)->setCulled(doBuffer);
        pos += item->size() + spacing;
        visibleItems.append(item);
        ++modelIndex;
        changed = true;
    }
 
    if (doBuffer && requestedIndex != -1) // already waiting for an item
        return changed;
 
    while (visibleIndex > 0 && visibleIndex <= model->count() && visiblePos > fillFrom) {
        if (!(item = static_cast<FxListItemSG*>(createItem(visibleIndex-1, incubationMode))))
            break;
        qCDebug(lcItemViewDelegateLifecycle) << "refill: prepend item" << visibleIndex-1 << "current top pos" << visiblePos << "buffer" << doBuffer << "item" << (QObject *)(item->item);
        --visibleIndex;
        visiblePos -= item->size() + spacing;
#if QT_CONFIG(quick_viewtransitions)
        if (!transitioner || !transitioner->canTransition(QQuickItemViewTransitioner::PopulateTransition, true)) // pos will be set by layoutVisibleItems()
#endif
            item->setPosition(visiblePos, true);
        if (item->item)
            QQuickItemPrivate::get(item->item)->setCulled(doBuffer);
        visibleItems.prepend(item);
        changed = true;
    }
 
    if (changed && sectionCriteria)
        updateSectionFocusOrder();
 
    return changed;
}
 
void QQuickListViewPrivate::removeItem(FxViewItem *item)
{
#if QT_CONFIG(quick_viewtransitions)
    if (item->transitionScheduledOrRunning()) {
        qCDebug(lcItemViewDelegateLifecycle) << "\tnot releasing animating item" << item->index << (QObject *)(item->item);
        item->releaseAfterTransition = true;
        releasePendingTransition.append(item);
    } else
#endif
    {
        qCDebug(lcItemViewDelegateLifecycle) << "\treleasing stationary item" << item->index << (QObject *)(item->item);
        if (auto *att = static_cast<QQuickListViewAttached*>(item->attached)) {
            releaseSectionItem(att->m_sectionItem);
            att->m_sectionItem = nullptr;
        }
        releaseItem(item, reusableFlag);
    }
}
 
bool QQuickListViewPrivate::removeNonVisibleItems(qreal bufferFrom, qreal bufferTo)
{
    FxViewItem *item = nullptr;
    bool changed = false;
 
    // Remove items from the start of the view.
    // Zero-sized items shouldn't be removed unless a non-zero-sized item is also being
    // removed, otherwise a zero-sized item is infinitely added and removed over and
    // over by refill().
    int index = 0;
    while (visibleItems.size() > 1 && index < visibleItems.size()
           && (item = visibleItems.at(index)) && item->endPosition() < bufferFrom) {
        if (item->attached->delayRemove())
            break;
 
        if (item->size() > 0) {
            qCDebug(lcItemViewDelegateLifecycle) << "refill: remove first" << visibleIndex << "top end pos" << item->endPosition();
            // remove this item and all zero-sized items before it
            while (item) {
                if (item->index != -1)
                    visibleIndex++;
                visibleItems.removeAt(index);
                removeItem(item);
                if (index == 0)
                    break;
                item = visibleItems.at(--index);
            }
            changed = true;
        } else {
            index++;
        }
    }
 
    while (visibleItems.size() > 1 && (item = visibleItems.constLast()) && item->position() > bufferTo) {
        if (item->attached->delayRemove())
            break;
        qCDebug(lcItemViewDelegateLifecycle) << "refill: remove last" << visibleIndex+visibleItems.size()-1 << item->position() << (QObject *)(item->item);
        visibleItems.removeLast();
        removeItem(item);
        changed = true;
    }
 
    return changed;
}
 
void QQuickListViewPrivate::visibleItemsChanged()
{
    if (visibleItems.size())
        visiblePos = (*visibleItems.constBegin())->position();
    updateAverage();
    if (currentIndex >= 0 && currentItem && !visibleItem(currentIndex)) {
        static_cast<FxListItemSG*>(currentItem)->setPosition(positionAt(currentIndex));
        updateHighlight();
    }
    if (sectionCriteria)
        updateCurrentSection();
    updateUnrequestedPositions();
}
 
void QQuickListViewPrivate::layoutVisibleItems(int fromModelIndex)
{
    if (!visibleItems.isEmpty()) {
        const qreal from = isContentFlowReversed() ? -position()-displayMarginBeginning-size() : position()-displayMarginBeginning;
        const qreal to = isContentFlowReversed() ? -position()+displayMarginEnd : position()+size()+displayMarginEnd;
 
        FxListItemSG *firstItem = static_cast<FxListItemSG *>(visibleItems.constFirst());
        bool fixedCurrent = currentItem && firstItem->item == currentItem->item;
 
#if QT_CONFIG(quick_viewtransitions)
        /* Set position of first item in list view when populate transition is configured, as it doesn't set
           while adding visible item (addVisibleItem()) to the view */
        if (transitioner && transitioner->canTransition(QQuickItemViewTransitioner::PopulateTransition, true))
            resetFirstItemPosition(isContentFlowReversed() ? -firstItem->position()-firstItem->size() : firstItem->position());
#endif
 
        firstVisibleItemPosition = firstItem->position();
        qreal sum = firstItem->size();
        qreal pos = firstItem->position() + firstItem->size() + spacing;
        firstItem->setVisible(firstItem->endPosition() >= from && firstItem->position() <= to);
 
        // setPosition will affect the position of the item, and its section, if it has one.
        // This will prevent them from potentially overlapping.
        if (firstItem->section())
            firstItem->setPosition(firstItem->position());
 
        for (int i=1; i < visibleItems.size(); ++i) {
            FxListItemSG *item = static_cast<FxListItemSG*>(visibleItems.at(i));
            if (item->index >= fromModelIndex) {
                item->setPosition(pos);
                item->setVisible(item->endPosition() >= from && item->position() <= to);
            }
            pos += item->size() + spacing;
            sum += item->size();
            fixedCurrent = fixedCurrent || (currentItem && item->item == currentItem->item);
        }
        averageSize = qRound(sum / visibleItems.size());
 
        // move current item if it is not a visible item.
        if (currentIndex >= 0 && currentItem && !fixedCurrent)
            static_cast<FxListItemSG*>(currentItem)->setPosition(positionAt(currentIndex));
 
        updateCurrentSection();
        updateStickySections();
        if (sectionCriteria)
            updateSectionFocusOrder();
    }
}
 
void QQuickListViewPrivate::repositionItemAt(FxViewItem *item, int index, qreal sizeBuffer)
{
    static_cast<FxListItemSG *>(item)->setPosition(positionAt(index) + sizeBuffer);
}
 
void QQuickListViewPrivate::repositionPackageItemAt(QQuickItem *item, int index)
{
    Q_Q(QQuickListView);
    qreal pos = position();
    if (orient == QQuickListView::Vertical) {
        if (item->y() + item->height() > pos && item->y() < pos + q->height()) {
            if (isBottomToTop())
                item->setY(-positionAt(index)-item->height());
            else
                item->setY(positionAt(index));
        }
    } else {
        if (item->x() + item->width() > pos && item->x() < pos + q->width()) {
            if (isRightToLeft())
                item->setX(-positionAt(index)-item->width());
            else
                item->setX(positionAt(index));
        }
    }
}
 
void QQuickListViewPrivate::resetFirstItemPosition(qreal pos)
{
    FxListItemSG *item = static_cast<FxListItemSG*>(visibleItems.constFirst());
    item->setPosition(pos);
}
 
void QQuickListViewPrivate::adjustFirstItem(qreal forwards, qreal backwards, int)
{
    if (!visibleItems.size())
        return;
    qreal diff = forwards - backwards;
    static_cast<FxListItemSG*>(visibleItems.constFirst())->setPosition(visibleItems.constFirst()->position() + diff);
}
 
void QQuickListViewPrivate::updateSizeChangesBeforeVisiblePos(FxViewItem *item, ChangeResult *removeResult)
{
    if (item != visibleItems.constFirst())
        QQuickItemViewPrivate::updateSizeChangesBeforeVisiblePos(item, removeResult);
}
 
void QQuickListViewPrivate::createHighlight(bool onDestruction)
{
    bool changed = false;
    if (highlight) {
        if (trackedItem == highlight.get())
            trackedItem = nullptr;
        highlight.reset();
 
        highlightPosAnimator.reset();
        highlightWidthAnimator.reset();
        highlightHeightAnimator.reset();
        highlightPosAnimator = nullptr;
        highlightWidthAnimator = nullptr;
        highlightHeightAnimator = nullptr;
 
        changed = true;
    }
 
    if (onDestruction)
        return;
 
    Q_Q(QQuickListView);
    if (currentItem) {
        QQuickItem *item = createHighlightItem();
        if (item) {
            std::unique_ptr<FxListItemSG> newHighlight
                    = std::make_unique<FxListItemSG>(item, q, true);
            newHighlight->trackGeometry(true);
 
            if (autoHighlight) {
                newHighlight->setSize(static_cast<FxListItemSG*>(currentItem)->itemSize());
                newHighlight->setPosition(static_cast<FxListItemSG*>(currentItem)->itemPosition());
            }
            const QLatin1String posProp(orient == QQuickListView::Vertical ? "y" : "x");
            highlightPosAnimator = std::make_unique<QSmoothedAnimation>();
            highlightPosAnimator->target = QQmlProperty(item, posProp);
            highlightPosAnimator->velocity = highlightMoveVelocity;
            highlightPosAnimator->userDuration = highlightMoveDuration;
 
            highlightWidthAnimator = std::make_unique<QSmoothedAnimation>();
            highlightWidthAnimator->velocity = highlightResizeVelocity;
            highlightWidthAnimator->userDuration = highlightResizeDuration;
            highlightWidthAnimator->target = QQmlProperty(item, QStringLiteral("width"));
 
            highlightHeightAnimator = std::make_unique<QSmoothedAnimation>();
            highlightHeightAnimator->velocity = highlightResizeVelocity;
            highlightHeightAnimator->userDuration = highlightResizeDuration;
            highlightHeightAnimator->target = QQmlProperty(item, QStringLiteral("height"));
 
            highlight = std::move(newHighlight);
            changed = true;
        }
    }
    if (changed)
        emit q->highlightItemChanged();
}
 
void QQuickListViewPrivate::updateHighlight()
{
    applyPendingChanges();
 
    if ((!currentItem && highlight) || (currentItem && !highlight))
        createHighlight();
    bool strictHighlight = haveHighlightRange && highlightRange == QQuickListView::StrictlyEnforceRange;
    if (currentItem && autoHighlight && highlight && (!strictHighlight || !pressed)) {
        // auto-update highlight
        FxListItemSG *listItem = static_cast<FxListItemSG*>(currentItem);
        highlightPosAnimator->to = isContentFlowReversed()
                ? -listItem->itemPosition()-listItem->itemSize()
                : listItem->itemPosition();
        highlightWidthAnimator->to = listItem->item->width();
        highlightHeightAnimator->to = listItem->item->height();
        if (orient == QQuickListView::Vertical) {
            if (highlight->item->width() == 0)
                highlight->item->setWidth(currentItem->item->width());
        } else {
            if (highlight->item->height() == 0)
                highlight->item->setHeight(currentItem->item->height());
        }
 
        highlightPosAnimator->restart();
        highlightWidthAnimator->restart();
        highlightHeightAnimator->restart();
    }
    updateTrackedItem();
}
 
void QQuickListViewPrivate::resetHighlightPosition()
{
    if (highlight && currentItem) {
        static_cast<FxListItemSG*>(highlight.get())->setPosition(
                static_cast<FxListItemSG*>(currentItem)->itemPosition());
    }
}
 
bool QQuickListViewPrivate::movingFromHighlight()
{
    if (!haveHighlightRange || highlightRange != QQuickListView::StrictlyEnforceRange)
        return false;
 
    return (highlightPosAnimator && highlightPosAnimator->isRunning()) ||
           (highlightHeightAnimator && highlightHeightAnimator->isRunning()) ||
           (highlightWidthAnimator && highlightWidthAnimator->isRunning());
}
 
 
QQuickItem * QQuickListViewPrivate::getSectionItem(const QString &section)
{
    Q_Q(QQuickListView);
    QQuickItem *sectionItem = nullptr;
    int i = sectionCacheSize-1;
    while (i >= 0 && !sectionCache[i])
        --i;
    if (i >= 0) {
        sectionItem = sectionCache[i];
        sectionCache[i] = nullptr;
        sectionItem->setVisible(true);
        QQmlContext *context = QQmlEngine::contextForObject(sectionItem)->parentContext();
        setSectionHelper(context, sectionItem, section);
    } else {
        QQmlComponent* delegate = sectionCriteria->delegate();
        const bool reuseExistingContext = delegate->isBound();
        auto delegatePriv = QQmlComponentPrivate::get(delegate);
        QQmlPropertyCache::ConstPtr rootPropertyCache;
 
        QQmlContext *creationContext = sectionCriteria->delegate()->creationContext();
        auto baseContext = creationContext ? creationContext : qmlContext(q);
        // if we need to insert a context property, we need a separate context
        QQmlContext *context = reuseExistingContext ? baseContext : new QQmlContext(baseContext);
        QObject *nobj = delegate->beginCreate(context);
        if (nobj) {
            if (delegatePriv->hadTopLevelRequiredProperties()) {
                delegate->setInitialProperties(nobj, {{QLatin1String("section"), section}});
            } else if (!reuseExistingContext) {
                context->setContextProperty(QLatin1String("section"), section);
            }
            if (!reuseExistingContext)
                QQml_setParent_noEvent(context, nobj);
            sectionItem = qobject_cast<QQuickItem *>(nobj);
            if (!sectionItem) {
                delete nobj;
            } else {
                if (qFuzzyIsNull(sectionItem->z()))
                    sectionItem->setZ(2);
                QQml_setParent_noEvent(sectionItem, contentItem);
                sectionItem->setParentItem(contentItem);
            }
            // sections are not controlled by FxListItemSG, so apply attached properties here
            auto *attached = static_cast<QQuickListViewAttached*>(qmlAttachedPropertiesObject<QQuickListView>(sectionItem));
            attached->setView(q);
        } else if (!reuseExistingContext) {
            delete context;
        }
        sectionCriteria->delegate()->completeCreate();
    }
 
    if (sectionItem)
        QQuickItemPrivate::get(sectionItem)->addItemChangeListener(this, QQuickItemPrivate::Geometry);
 
    return sectionItem;
}
 
void QQuickListViewPrivate::releaseSectionItem(QQuickItem *item)
{
    if (!item)
        return;
    int i = 0;
 
    QQuickItemPrivate::get(item)->removeItemChangeListener(this, QQuickItemPrivate::Geometry);
 
    do {
        if (!sectionCache[i]) {
            sectionCache[i] = item;
            sectionCache[i]->setVisible(false);
            return;
        }
        ++i;
    } while (i < sectionCacheSize);
    delete item;
}
 
 
void QQuickListViewPrivate::releaseSectionItems()
{
    for (FxViewItem *item : std::as_const(visibleItems)) {
        FxListItemSG *listItem = static_cast<FxListItemSG *>(item);
        if (listItem->section()) {
            qreal pos = listItem->position();
            releaseSectionItem(listItem->section());
            listItem->setSection(nullptr);
            listItem->setPosition(pos);
        }
    }
    for (int i = 0; i < sectionCacheSize; ++i) {
        delete sectionCache[i];
        sectionCache[i] = nullptr;
    }
}
 
void QQuickListViewPrivate::updateInlineSection(FxListItemSG *listItem)
{
    if (!sectionCriteria || !sectionCriteria->delegate())
        return;
    if (QString::compare(listItem->attached->m_prevSection, listItem->attached->m_section, Qt::CaseInsensitive)
            && (sectionCriteria->labelPositioning() & QQuickViewSection::InlineLabels
                || (listItem->index == 0 && sectionCriteria->labelPositioning() & QQuickViewSection::CurrentLabelAtStart))) {
        if (!listItem->section()) {
            qreal pos = listItem->position();
            listItem->setSection(getSectionItem(listItem->attached->m_section));
            listItem->setPosition(pos);
        } else {
            QQmlContext *context = QQmlEngine::contextForObject(listItem->section())->parentContext();
            setSectionHelper(context, listItem->section(), listItem->attached->m_section);
        }
    } else if (listItem->section()) {
        qreal pos = listItem->position();
        releaseSectionItem(listItem->section());
        listItem->setSection(nullptr);
        listItem->setPosition(pos);
    }
}
 
/*!
    \internal
 
    Keeps the Tab/backtab focus order of the section headers and delegate
    items aligned with their visual (top-to-bottom) order.
 
    Tab navigation between sibling items follows the contentItem's
    child-stacking order (see QQuickItemPrivate::nextTabChildItem()), not their
    visual geometry. Delegate items and their inline section headers are
    parented to the contentItem in creation order, which need not match the
    visual order: a section header is created after the delegate item it
    precedes, and items added while flicking backwards are appended to the
    child list.
 
    To make the focus chain follow the visual order, re-stack the visible
    delegate items and their section headers so that each section header comes
    immediately before its delegate item. stackAfter() is a no-op when an item
    is already in place, so this is inexpensive for a stable view. Only items
    in visibleItems are touched; the header, footer, highlight and sticky
    section items are left untouched, and z values are unchanged so the visual
    stacking order is unaffected.
*/
void QQuickListViewPrivate::updateSectionFocusOrder()
{
    if (!sectionCriteria || visibleItems.isEmpty())
        return;
 
    QQuickItem *prev = nullptr;
    for (FxViewItem *viewItem : std::as_const(visibleItems)) {
        auto *listItem = static_cast<FxListItemSG *>(viewItem);
        if (QQuickItem *section = listItem->section()) {
            if (prev)
                section->stackAfter(prev);
            prev = section;
        }
        if (QQuickItem *item = listItem->item) {
            if (prev)
                item->stackAfter(prev);
            prev = item;
        }
    }
}
 
void QQuickListViewPrivate::updateStickySections()
{
    if (!sectionCriteria || !sectionCriteria->delegate()
            || (!sectionCriteria->labelPositioning() && !currentSectionItem && !nextSectionItem))
        return;
 
    bool isFlowReversed = isContentFlowReversed();
    qreal viewPos = isFlowReversed ? -position()-size() : position();
    qreal startPos = hasStickyHeader() ? header->endPosition() : viewPos;
    qreal endPos = hasStickyFooter() ? footer->position() : viewPos + size();
 
    QQuickItem *sectionItem = nullptr;
    QQuickItem *lastSectionItem = nullptr;
    int index = 0;
    while (index < visibleItems.size()) {
        if (QQuickItem *section = static_cast<FxListItemSG *>(visibleItems.at(index))->section()) {
            // Find the current section header and last visible section header
            // and hide them if they will overlap a static section header.
            qreal sectionPos = orient == QQuickListView::Vertical ? section->y() : section->x();
            qreal sectionSize = orient == QQuickListView::Vertical ? section->height() : section->width();
            bool visTop = true;
            if (sectionCriteria->labelPositioning() & QQuickViewSection::CurrentLabelAtStart)
                visTop = isFlowReversed ? -sectionPos-sectionSize >= startPos : sectionPos >= startPos;
            bool visBot = true;
            if (sectionCriteria->labelPositioning() & QQuickViewSection::NextLabelAtEnd)
                visBot = isFlowReversed ? -sectionPos <= endPos : sectionPos + sectionSize < endPos;
            section->setVisible(visBot && visTop);
            if (visTop && !sectionItem)
                sectionItem = section;
            if (isFlowReversed) {
               if (-sectionPos <= endPos)
                    lastSectionItem = section;
            } else {
                if (sectionPos + sectionSize < endPos)
                    lastSectionItem = section;
            }
        }
        ++index;
    }
 
    // Current section header
    if (sectionCriteria->labelPositioning() & QQuickViewSection::CurrentLabelAtStart && isValid() && visibleItems.size()) {
        if (!currentSectionItem) {
            currentSectionItem = getSectionItem(currentSection);
        } else if (QString::compare(currentStickySection, currentSection, Qt::CaseInsensitive)) {
            QQmlContext *context = QQmlEngine::contextForObject(currentSectionItem)->parentContext();
            setSectionHelper(context, currentSectionItem, currentSection);
        }
        currentStickySection = currentSection;
        if (!currentSectionItem)
            return;
 
        qreal sectionSize = orient == QQuickListView::Vertical ? currentSectionItem->height() : currentSectionItem->width();
        bool atBeginning = orient == QQuickListView::Vertical ? (isBottomToTop() ? vData.atEnd : vData.atBeginning) : (isRightToLeft() ? hData.atEnd : hData.atBeginning);
 
        currentSectionItem->setVisible(!atBeginning && (!header || hasStickyHeader() || header->endPosition() < viewPos));
        qreal pos = isFlowReversed ? position() + size() - sectionSize : startPos;
        if (header)
            pos = isFlowReversed ? qMin(-header->endPosition() - sectionSize, pos) : qMax(header->endPosition(), pos);
        if (sectionItem) {
            qreal sectionPos = orient == QQuickListView::Vertical ? sectionItem->y() : sectionItem->x();
            pos = isFlowReversed ? qMax(pos, sectionPos + sectionSize) : qMin(pos, sectionPos - sectionSize);
        }
        if (footer)
            pos = isFlowReversed ? qMax(-footer->position(), pos) : qMin(footer->position() - sectionSize, pos);
        if (orient == QQuickListView::Vertical)
            currentSectionItem->setY(pos);
        else
            currentSectionItem->setX(pos);
    } else if (currentSectionItem) {
        releaseSectionItem(currentSectionItem);
        currentSectionItem = nullptr;
    }
 
    // Next section footer
    if (sectionCriteria->labelPositioning() & QQuickViewSection::NextLabelAtEnd && isValid() && visibleItems.size()) {
        if (!nextSectionItem) {
            nextSectionItem = getSectionItem(nextSection);
        } else if (QString::compare(nextStickySection, nextSection, Qt::CaseInsensitive)) {
            QQmlContext *context = QQmlEngine::contextForObject(nextSectionItem)->parentContext();
            setSectionHelper(context, nextSectionItem, nextSection);
        }
        nextStickySection = nextSection;
        if (!nextSectionItem)
            return;
 
        qreal sectionSize = orient == QQuickListView::Vertical ? nextSectionItem->height() : nextSectionItem->width();
        nextSectionItem->setVisible(!nextSection.isEmpty());
        qreal pos = isFlowReversed ? position() : endPos - sectionSize;
        if (footer)
            pos = isFlowReversed ? qMax(-footer->position(), pos) : qMin(footer->position() - sectionSize, pos);
        if (lastSectionItem) {
            qreal sectionPos = orient == QQuickListView::Vertical ? lastSectionItem->y() : lastSectionItem->x();
            pos = isFlowReversed ? qMin(pos, sectionPos - sectionSize) : qMax(pos, sectionPos + sectionSize);
        }
        if (header)
            pos = isFlowReversed ? qMin(-header->endPosition() - sectionSize, pos) : qMax(header->endPosition(), pos);
        if (orient == QQuickListView::Vertical)
            nextSectionItem->setY(pos);
        else
            nextSectionItem->setX(pos);
    } else if (nextSectionItem) {
        releaseSectionItem(nextSectionItem);
        nextSectionItem = nullptr;
    }
}
 
void QQuickListViewPrivate::updateSections()
{
    Q_Q(QQuickListView);
    if (!q->isComponentComplete())
        return;
 
    QQuickItemViewPrivate::updateSections();
 
    if (sectionCriteria && !visibleItems.isEmpty() && isValid()) {
        QString prevSection;
        if (visibleIndex > 0)
            prevSection = sectionAt(visibleIndex-1);
        QQuickListViewAttached *prevAtt = nullptr;
        int prevIdx = -1;
        int idx = -1;
        for (FxViewItem *item : std::as_const(visibleItems)) {
            QQuickListViewAttached *attached = static_cast<QQuickListViewAttached*>(item->attached);
            attached->setPrevSection(prevSection);
            if (item->index != -1) {
                QString propValue = model->stringValue(item->index, sectionCriteria->property());
                attached->setSection(sectionCriteria->sectionString(propValue));
                idx = item->index;
            }
            updateInlineSection(static_cast<FxListItemSG*>(item));
            if (prevAtt)
                prevAtt->setNextSection(sectionAt(prevIdx+1));
            prevSection = attached->section();
            prevAtt = attached;
            prevIdx = item->index;
        }
        if (prevAtt) {
            if (idx > 0 && idx < model->count()-1)
                prevAtt->setNextSection(sectionAt(idx+1));
            else
                prevAtt->setNextSection(QString());
        }
        updateSectionFocusOrder();
    }
 
    lastVisibleSection = QString();
}
 
void QQuickListViewPrivate::updateCurrentSection()
{
    Q_Q(QQuickListView);
    if (!sectionCriteria || visibleItems.isEmpty()) {
        if (!currentSection.isEmpty()) {
            currentSection.clear();
            emit q->currentSectionChanged();
        }
        return;
    }
    bool inlineSections = sectionCriteria->labelPositioning() & QQuickViewSection::InlineLabels;
    qreal viewPos = isContentFlowReversed() ? -position()-size() : position();
    qreal startPos = hasStickyHeader() ? header->endPosition() : viewPos;
    int index = 0;
    int modelIndex = visibleIndex;
    while (index < visibleItems.size()) {
        FxViewItem *item = visibleItems.at(index);
        if (item->endPosition() > startPos)
            break;
        if (item->index != -1)
            modelIndex = item->index;
        ++index;
    }
 
    QString newSection = currentSection;
    if (index < visibleItems.size())
        newSection = visibleItems.at(index)->attached->section();
    else
        newSection = (*visibleItems.constBegin())->attached->section();
    if (newSection != currentSection) {
        currentSection = newSection;
        updateStickySections();
        emit q->currentSectionChanged();
    }
 
    if (sectionCriteria->labelPositioning() & QQuickViewSection::NextLabelAtEnd) {
        // Don't want to scan for next section on every movement, so remember
        // the last section in the visible area and only scan for the next
        // section when that changes.  Clearing lastVisibleSection will also
        // force searching.
        QString lastSection = currentSection;
        qreal endPos = hasStickyFooter() ? footer->position() : viewPos + size();
        if (nextSectionItem && !inlineSections)
            endPos -= orient == QQuickListView::Vertical ? nextSectionItem->height() : nextSectionItem->width();
        while (index < visibleItems.size()) {
            FxListItemSG *listItem = static_cast<FxListItemSG *>(visibleItems.at(index));
            if (listItem->itemPosition() >= endPos)
                break;
            if (listItem->index != -1)
                modelIndex = listItem->index;
            lastSection = listItem->attached->section();
            ++index;
        }
 
        if (lastVisibleSection != lastSection) {
            nextSection = QString();
            lastVisibleSection = lastSection;
            for (int i = modelIndex; i < itemCount; ++i) {
                QString section = sectionAt(i);
                if (section != lastSection) {
                    nextSection = section;
                    updateStickySections();
                    break;
                }
            }
        }
    }
}
 
void QQuickListViewPrivate::initializeCurrentItem()
{
    QQuickItemViewPrivate::initializeCurrentItem();
 
    if (currentItem) {
        FxListItemSG *listItem = static_cast<FxListItemSG *>(currentItem);
 
        // don't reposition the item if it is already in the visibleItems list
        FxViewItem *actualItem = visibleItem(currentIndex);
        if (!actualItem) {
            if (currentIndex == visibleIndex - 1 && visibleItems.size()) {
                // We can calculate exact postion in this case
                listItem->setPosition(visibleItems.constFirst()->position() - currentItem->size() - spacing);
            } else {
                // Create current item now and position as best we can.
                // Its position will be corrected when it becomes visible.
                listItem->setPosition(positionAt(currentIndex));
            }
        }
 
        if (visibleItems.isEmpty())
            averageSize = listItem->size();
    }
}
 
void QQuickListViewPrivate::updateAverage()
{
    if (!visibleItems.size())
        return;
    qreal sum = 0.0;
    for (FxViewItem *item : std::as_const(visibleItems))
        sum += item->size();
    averageSize = qRound(sum / visibleItems.size());
}
 
qreal QQuickListViewPrivate::headerSize() const
{
    return header ? header->size() : 0.0;
}
 
qreal QQuickListViewPrivate::footerSize() const
{
    return footer ? footer->size() : 0.0;
}
 
bool QQuickListViewPrivate::showHeaderForIndex(int index) const
{
    return index == 0;
}
 
bool QQuickListViewPrivate::showFooterForIndex(int index) const
{
    return model && index == model->count()-1;
}
 
void QQuickListViewPrivate::updateFooter()
{
    Q_Q(QQuickListView);
    bool created = false;
    if (!footer) {
        QQuickItem *item = createComponentItem(footerComponent, 1.0);
        if (!item)
            return;
        footer = new FxListItemSG(item, q, true);
        footer->trackGeometry(true);
        created = true;
    }
 
    FxListItemSG *listItem = static_cast<FxListItemSG*>(footer);
    if (footerPositioning == QQuickListView::OverlayFooter) {
        listItem->setPosition(isContentFlowReversed() ? -position() - footerSize() : position() + size() - footerSize(), false, false);
    } else if (visibleItems.size()) {
        if (footerPositioning == QQuickListView::PullBackFooter) {
            qreal viewPos = isContentFlowReversed() ? -position() : position() + size();
            // using qBound() would throw an assert here, because max < min is a valid case
            // here, if the list's delegates do not fill the whole view
            qreal clampedPos = qMax(originPosition() - footerSize() + size(), qMin(listItem->position(), lastPosition()));
            listItem->setPosition(qBound(viewPos - footerSize(), clampedPos, viewPos), false, false);
        } else {
            qreal endPos = lastPosition();
            if (findLastVisibleIndex() == model->count()-1) {
                listItem->setPosition(endPos, false, false);
            } else {
                qreal visiblePos = position() + q->height();
                if (endPos <= visiblePos || listItem->position() < endPos)
                    listItem->setPosition(endPos, false, false);
            }
        }
    } else {
        listItem->setPosition(visiblePos, false, false);
    }
 
    if (created)
        emit q->footerItemChanged();
}
 
void QQuickListViewPrivate::fixupHeaderCompleted()
{
    headerNeedsSeparateFixup = false;
    QObjectPrivate::disconnect(&timeline, &QQuickTimeLine::updated, this, &QQuickListViewPrivate::fixupHeader);
}
 
void QQuickListViewPrivate::fixupHeader()
{
    FxListItemSG *listItem = static_cast<FxListItemSG*>(header);
    const bool fixingUp = (orient == QQuickListView::Vertical ? vData : hData).fixingUp;
    if (fixingUp && headerPositioning == QQuickListView::PullBackHeader && visibleItems.size()) {
        int fixupDura = timeline.duration();
        if (fixupDura < 0)
            fixupDura = fixupDuration/2;
        const int t = timeline.time();
 
        const qreal progress = qreal(t)/fixupDura;
        const qreal ultimateHeaderPosition = desiredHeaderVisible ? desiredViewportPosition : desiredViewportPosition - headerSize();
        const qreal headerPosition = fixupHeaderPosition * (1 - progress) + ultimateHeaderPosition * progress;
        const qreal viewPos = isContentFlowReversed() ? -position() - size() : position();
        const qreal clampedPos = qBound(originPosition() - headerSize(), headerPosition, lastPosition() - size());
        listItem->setPosition(qBound(viewPos - headerSize(), clampedPos, viewPos));
    }
}
 
void QQuickListViewPrivate::updateHeader()
{
    Q_Q(QQuickListView);
    bool created = false;
    if (!header) {
        QQuickItem *item = createComponentItem(headerComponent, 1.0);
        if (!item)
            return;
        header = new FxListItemSG(item, q, true);
        header->trackGeometry(true);
        created = true;
    }
 
    FxListItemSG *listItem = static_cast<FxListItemSG*>(header);
    if (headerPositioning == QQuickListView::OverlayHeader) {
        listItem->setPosition(isContentFlowReversed() ? -position() - size() : position(), false, false);
    } else if (visibleItems.size()) {
        const bool fixingUp = (orient == QQuickListView::Vertical ? vData : hData).fixingUp;
        if (headerPositioning == QQuickListView::PullBackHeader) {
            qreal headerPosition = listItem->position();
            const qreal viewPos = isContentFlowReversed() ? -position() - size() : position();
            // Make sure the header is not shown if we absolutely do not have any plans to show it
            if (fixingUp && !headerNeedsSeparateFixup)
                headerPosition = viewPos - headerSize();
            // using qBound() would throw an assert here, because max < min is a valid case
            // here, if the list's delegates do not fill the whole view
            qreal clampedPos = qMax(originPosition() - headerSize(), qMin(headerPosition, lastPosition() - size()));
            listItem->setPosition(qBound(viewPos - headerSize(), clampedPos, viewPos), false, false);
        } else {
            qreal startPos = originPosition();
            if (visibleIndex == 0) {
                listItem->setPosition(startPos - headerSize(), false, false);
            } else {
                if (position() <= startPos || listItem->position() > startPos - headerSize())
                    listItem->setPosition(startPos - headerSize(), false, false);
            }
        }
    } else {
        listItem->setPosition(-headerSize(), false, false);
    }
 
    if (created)
        emit q->headerItemChanged();
}
 
bool QQuickListViewPrivate::hasStickyHeader() const
{
    return header && headerPositioning != QQuickListView::InlineHeader;
}
 
bool QQuickListViewPrivate::hasStickyFooter() const
{
    return footer && footerPositioning != QQuickListView::InlineFooter;
}
 
void QQuickListViewPrivate::initializeComponentItem(QQuickItem *item) const
{
    QQuickListViewAttached *attached = static_cast<QQuickListViewAttached *>(
            qmlAttachedPropertiesObject<QQuickListView>(item));
    if (attached) // can be null for default components (see createComponentItem)
        attached->setView(const_cast<QQuickListView*>(q_func()));
}
 
void QQuickListViewPrivate::itemGeometryChanged(QQuickItem *item, QQuickGeometryChange change,
                                                const QRectF &oldGeometry)
{
    Q_Q(QQuickListView);
 
    QQuickItemViewPrivate::itemGeometryChanged(item, change, oldGeometry);
    if (!q->isComponentComplete())
        return;
 
    if (currentItem && currentItem->item == item) {
        const bool contentFlowReversed = isContentFlowReversed();
        const qreal pos = position();
        const qreal sz = size();
        const qreal from = contentFlowReversed ? -pos - displayMarginBeginning - sz : pos - displayMarginBeginning;
        const qreal to = contentFlowReversed ? -pos + displayMarginEnd : pos + sz + displayMarginEnd;
        QQuickItemPrivate::get(currentItem->item)->setCulled(currentItem->endPosition() < from || currentItem->position() > to);
    }
 
    if (item != contentItem && (!highlight || item != highlight->item)) {
        if ((orient == QQuickListView::Vertical && change.heightChange())
            || (orient == QQuickListView::Horizontal && change.widthChange())) {
 
            // if visibleItems.first() has resized, adjust its pos since it is used to
            // position all subsequent items
            if (visibleItems.size() && item == visibleItems.constFirst()->item) {
                FxListItemSG *listItem = static_cast<FxListItemSG*>(visibleItems.constFirst());
#if QT_CONFIG(quick_viewtransitions)
                if (listItem->transitionScheduledOrRunning())
                    return;
#endif
                if (orient == QQuickListView::Vertical) {
                    const qreal oldItemEndPosition = verticalLayoutDirection == QQuickItemView::BottomToTop ? -oldGeometry.y() : oldGeometry.y() + oldGeometry.height();
                    const qreal heightDiff = item->height() - oldGeometry.height();
                    if (verticalLayoutDirection == QQuickListView::TopToBottom && oldItemEndPosition < q->contentY())
                        listItem->setPosition(listItem->position() - heightDiff, true);
                    else if (verticalLayoutDirection == QQuickListView::BottomToTop && oldItemEndPosition > q->contentY())
                        listItem->setPosition(listItem->position() + heightDiff, true);
                } else {
                    const qreal oldItemEndPosition = q->effectiveLayoutDirection() == Qt::RightToLeft ? -oldGeometry.x() : oldGeometry.x() + oldGeometry.width();
                    const qreal widthDiff = item->width() - oldGeometry.width();
                    if (q->effectiveLayoutDirection() == Qt::LeftToRight && oldItemEndPosition < q->contentX())
                        listItem->setPosition(listItem->position() - widthDiff, true);
                    else if (q->effectiveLayoutDirection() == Qt::RightToLeft && oldItemEndPosition > q->contentX())
                        listItem->setPosition(listItem->position() + widthDiff, true);
                }
            }
            forceLayoutPolish();
        }
    }
}
 
void QQuickListViewPrivate::fixupPosition()
{
    if (orient == QQuickListView::Vertical)
        fixupY();
    else
        fixupX();
    snapResizeTargetIndex = -1;
}
 
void QQuickListViewPrivate::fixup(AxisData &data, qreal minExtent, qreal maxExtent)
{
    if (orient == QQuickListView::Horizontal && &data == &vData) {
        if (flickableDirection != QQuickFlickable::HorizontalFlick)
            QQuickItemViewPrivate::fixup(data, minExtent, maxExtent);
        return;
    } else if (orient == QQuickListView::Vertical && &data == &hData) {
        if (flickableDirection != QQuickFlickable::VerticalFlick)
            QQuickItemViewPrivate::fixup(data, minExtent, maxExtent);
        return;
    }
 
    // update footer if all visible items have been removed
    if (visibleItems.size() == 0)
        updateFooter();
 
    correctFlick = false;
    fixupMode = moveReason == Mouse ? fixupMode : Immediate;
    bool strictHighlightRange = haveHighlightRange && highlightRange == QQuickListView::StrictlyEnforceRange;
 
    qreal viewPos = isContentFlowReversed() ? -position()-size() : position();
 
    if (snapMode != QQuickListView::NoSnap && moveReason != QQuickListViewPrivate::SetIndex) {
        /*
        There are many ways items can "snap" (align) when a flick by mouse/touch is about to end.
        The following table describes how things are snapped for a TopToBottom ListView (the
        behavior of the other orientations can be derived from TopToBottom):
 
        | header\\range     | No highlight range            | Has a highlight range |
        |------------------ | ----------------------------- | --------------------- |
        | No header         | Snaps to ListView top         | Snaps to preferredHighlightBegin position [1] |
        | InlineHeader      | Snaps to ListView top         | Snaps to preferredHighlightBegin position [1] |
        | OverlayHeader     | Snaps to header               | Snaps to neither [!] |
        | PullbackHeader    | Snaps to header/ListView top  | Snaps to preferredHighlightBegin when header is pulled back. Snaps to neither when header is pulled in. |
 
        Notes:
        [1]: If there is no item below preferredHighlightBegin, it will snap to preferredHighlightEnd
        [!]: This is likely not intended behavior
        */
        qreal tempPosition = isContentFlowReversed() ? -position()-size() : position();
        if (snapMode == QQuickListView::SnapOneItem && moveReason == Mouse) {
            // if we've been dragged < averageSize/2 then bias towards the next item
            qreal dist = data.move.value() - data.pressPos;
            qreal bias = 0;
            if (data.velocity > 0 && dist > QML_FLICK_SNAPONETHRESHOLD && dist < averageSize/2)
                bias = averageSize/2;
            else if (data.velocity < 0 && dist < -QML_FLICK_SNAPONETHRESHOLD && dist > -averageSize/2)
                bias = -averageSize/2;
            if (isContentFlowReversed())
                bias = -bias;
            tempPosition -= bias;
        }
 
        qreal snapOffset = 0;
        qreal overlayHeaderOffset = 0;
        bool isHeaderWithinBounds = false;
        if (header) {
            qreal visiblePartOfHeader = header->position() + header->size() - tempPosition;
            isHeaderWithinBounds = visiblePartOfHeader > 0;
            switch (headerPositioning) {
            case QQuickListView::OverlayHeader:
                snapOffset = header->size();
                overlayHeaderOffset = header->size();
                break;
            case QQuickListView::InlineHeader:
                if (isHeaderWithinBounds && tempPosition < originPosition())
                    // For the inline header, we want to snap to the first item
                    // if we're more than halfway down the inline header.
                    // So if we look for an item halfway down of the header
                    snapOffset = header->size() / 2;
                break;
            case QQuickListView::PullBackHeader:
                desiredHeaderVisible = visiblePartOfHeader > header->size()/2;
                if (qFuzzyCompare(header->position(), tempPosition)) {
                    // header was pulled down; make sure it remains visible and snap items to bottom of header
                    snapOffset = header->size();
                } else if (desiredHeaderVisible) {
                    // More than 50% of the header is shown. Show it fully.
                    // Scroll the view so the next item snaps to the header.
                    snapOffset = header->size();
                    overlayHeaderOffset = header->size();
                }
                break;
            }
        }
 
        // If there are pending changes, the item returned from snapItemAt might get deleted as
        // soon as applyPendingChanges() is called (from e.g. updateHighlight()).
        // Therefore, apply the pending changes before we call snapItemAt()
        if (strictHighlightRange)
            updateHighlight();
 
        FxViewItem *topItem = nullptr;
        FxViewItem *bottomItem = nullptr;
        if (snapResizeTargetIndex >= 0) {
            topItem = visibleItem(snapResizeTargetIndex);
            bottomItem = topItem;
        }
        if (!topItem)
            topItem = snapItemAt(tempPosition + snapOffset + highlightRangeStart);
        if (!bottomItem)
            bottomItem = snapItemAt(tempPosition + snapOffset + highlightRangeEnd);
        if (strictHighlightRange && currentItem) {
            // StrictlyEnforceRange always keeps an item in range
            if (!topItem || (topItem->index != currentIndex && fixupMode == Immediate))
                topItem = currentItem;
            if (!bottomItem || (bottomItem->index != currentIndex && fixupMode == Immediate))
                bottomItem = currentItem;
        }
 
        qreal pos = 0;
        bool isInBounds = -position() > maxExtent && -position() <= minExtent;
 
        if (header && !topItem && isInBounds) {
            // We are trying to pull back further than needed
            switch (headerPositioning) {
            case QQuickListView::OverlayHeader:
                pos = startPosition() - overlayHeaderOffset;
                break;
            case QQuickListView::InlineHeader:
                pos = isContentFlowReversed() ? header->size() - size() : header->position();
                break;
            case QQuickListView::PullBackHeader:
                pos = isContentFlowReversed() ? -size() : startPosition();
                break;
            }
        } else if (topItem && (isInBounds || strictHighlightRange)) {
            if (topItem->index == 0 && header && !hasStickyHeader() && tempPosition+highlightRangeStart < header->position()+header->size()/2 && !strictHighlightRange) {
                pos = isContentFlowReversed() ? -header->position() + highlightRangeStart - size() : (header->position() - highlightRangeStart + header->size());
            } else {
                if (header && headerPositioning == QQuickListView::PullBackHeader) {
                    // We pulled down the header. If it isn't pulled all way down, we need to snap
                    // the header.
                    if (qFuzzyCompare(tempPosition, header->position())) {
                        // It is pulled all way down. Scroll-snap the content, but not the header.
                        if (isContentFlowReversed())
                            pos = -static_cast<FxListItemSG*>(topItem)->itemPosition() + highlightRangeStart - size() + snapOffset;
                        else
                            pos = static_cast<FxListItemSG*>(topItem)->itemPosition() - highlightRangeStart - snapOffset;
                    } else {
                        // Header is not pulled all way down, make it completely visible or hide it.
                        // Depends on how much of the header is visible.
                        if (desiredHeaderVisible) {
                            // More than half of the header is visible - show it.
                            // Scroll so that the topItem is aligned to a fully visible header
                            if (isContentFlowReversed())
                                pos = -static_cast<FxListItemSG*>(topItem)->itemPosition() + highlightRangeStart - size() + headerSize();
                            else
                                pos = static_cast<FxListItemSG*>(topItem)->itemPosition() - highlightRangeStart - headerSize();
                        } else {
                            // Less than half is visible - hide the header. Scroll so
                            // that the topItem is aligned to the top of the view
                            if (isContentFlowReversed())
                                pos = -static_cast<FxListItemSG*>(topItem)->itemPosition() + highlightRangeStart - size();
                            else
                                pos = static_cast<FxListItemSG*>(topItem)->itemPosition() - highlightRangeStart;
                        }
                    }
 
                    headerNeedsSeparateFixup = isHeaderWithinBounds || desiredHeaderVisible;
                    if (headerNeedsSeparateFixup) {
                        // We need to animate the header independently if it starts visible or should end as visible,
                        // since the header should not necessarily follow the content.
                        // Store the desired viewport position.
                        // Also store the header position so we know where to animate the header from (fixupHeaderPosition).
                        // We deduce the desired header position from the desiredViewportPosition variable.
                        pos = qBound(-minExtent, pos, -maxExtent);
                        desiredViewportPosition = isContentFlowReversed() ? -pos - size() : pos;
 
                        FxListItemSG *headerItem = static_cast<FxListItemSG*>(header);
                        fixupHeaderPosition = headerItem->position();
 
                        // follow the same fixup timeline
                        QObjectPrivate::connect(&timeline, &QQuickTimeLine::updated, this, &QQuickListViewPrivate::fixupHeader);
                        QObjectPrivate::connect(&timeline, &QQuickTimeLine::completed, this, &QQuickListViewPrivate::fixupHeaderCompleted);
                    }
                } else if (isContentFlowReversed()) {
                    pos = -static_cast<FxListItemSG*>(topItem)->itemPosition() + highlightRangeStart - size() + overlayHeaderOffset;
                } else {
                    pos = static_cast<FxListItemSG*>(topItem)->itemPosition() - highlightRangeStart - overlayHeaderOffset;
                }
            }
        } else if (bottomItem && isInBounds) {
            if (isContentFlowReversed())
                pos = -static_cast<FxListItemSG*>(bottomItem)->itemPosition() + highlightRangeEnd - size() + overlayHeaderOffset;
            else
                pos = static_cast<FxListItemSG*>(bottomItem)->itemPosition() - highlightRangeEnd - overlayHeaderOffset;
        } else {
            QQuickItemViewPrivate::fixup(data, minExtent, maxExtent);
            return;
        }
        // If we have the CurrentLabelAtStart flag set, then we need to consider
        // the section size while calculating the position
        if (sectionCriteria
            && (sectionCriteria->labelPositioning() & QQuickViewSection::CurrentLabelAtStart)
            && currentSectionItem) {
            auto sectionSize = (orient == QQuickListView::Vertical) ? currentSectionItem->height()
                                                                    : currentSectionItem->width();
            if (isContentFlowReversed())
                pos += sectionSize;
            else
                pos -= sectionSize;
        }
 
        pos = qBound(-minExtent, pos, -maxExtent);
 
        qreal dist = qAbs(data.move + pos);
        if (dist >= 0) {
            // Even if dist == 0 we still start the timeline, because we use the same timeline for
            // moving the header. And we might need to move the header while the content does not
            // need moving
            timeline.reset(data.move);
            if (fixupMode != Immediate) {
                timeline.move(data.move, -pos, QEasingCurve(QEasingCurve::InOutQuad), fixupDuration/2);
                data.fixingUp = true;
            } else {
                timeline.set(data.move, -pos);
            }
            vTime = timeline.time();
        }
    } else if (currentItem && strictHighlightRange && moveReason != QQuickListViewPrivate::SetIndex) {
        updateHighlight();
        qreal pos = static_cast<FxListItemSG*>(currentItem)->itemPosition();
        if (viewPos < pos + static_cast<FxListItemSG*>(currentItem)->itemSize() - highlightRangeEnd)
            viewPos = pos + static_cast<FxListItemSG*>(currentItem)->itemSize() - highlightRangeEnd;
        if (viewPos > pos - highlightRangeStart)
            viewPos = pos - highlightRangeStart;
        if (isContentFlowReversed())
            viewPos = -viewPos-size();
 
        timeline.reset(data.move);
        if (viewPos != position()) {
            if (fixupMode != Immediate) {
                if (fixupMode == ExtentChanged && data.fixingUp)
                    timeline.move(data.move, -viewPos, QEasingCurve(QEasingCurve::OutQuad), fixupDuration/2);
                else
                    timeline.move(data.move, -viewPos, QEasingCurve(QEasingCurve::InOutQuad), fixupDuration/2);
                data.fixingUp = true;
            } else {
                timeline.set(data.move, -viewPos);
            }
        }
        vTime = timeline.time();
    } else {
        QQuickItemViewPrivate::fixup(data, minExtent, maxExtent);
    }
    data.inOvershoot = false;
    fixupMode = Normal;
}
 
bool QQuickListViewPrivate::flick(AxisData &data, qreal minExtent, qreal maxExtent, qreal vSize,
                                        QQuickTimeLineCallback::Callback fixupCallback, QEvent::Type eventType, qreal velocity)
{
    data.fixingUp = false;
    moveReason = Mouse;
    if ((!haveHighlightRange || highlightRange != QQuickListView::StrictlyEnforceRange) && snapMode == QQuickListView::NoSnap) {
        correctFlick = true;
        return QQuickItemViewPrivate::flick(data, minExtent, maxExtent, vSize, fixupCallback, eventType, velocity);
    }
    qreal maxDistance = 0;
    const qreal dataValue =
            isContentFlowReversed() ? -data.move.value() + size() : data.move.value();
 
    // -ve velocity means list is moving up/left
    if (velocity > 0) {
        if (data.move.value() < minExtent) {
            if (snapMode == QQuickListView::SnapOneItem && !hData.flicking && !vData.flicking) {
                // averageSize/2 + 1 - next item
                qreal bias = averageSize / 2 + 1 - (pressed ? data.pressPos : 0);
                if (isContentFlowReversed())
                    bias = -bias;
                data.flickTarget = -snapPosAt(-(dataValue - highlightRangeStart) - bias) + highlightRangeStart;
                maxDistance = qAbs(data.flickTarget - data.move.value());
                velocity = maxVelocity;
            } else {
                maxDistance = qAbs(minExtent - data.move.value());
            }
        }
        if (snapMode == QQuickListView::NoSnap && highlightRange != QQuickListView::StrictlyEnforceRange)
            data.flickTarget = minExtent;
    } else {
        if (data.move.value() > maxExtent) {
            if (snapMode == QQuickListView::SnapOneItem && !hData.flicking && !vData.flicking) {
                // averageSize/2 + 1 - next item
                qreal bias = averageSize / 2 + 1 - (pressed ? data.pressPos : 0);
                if (isContentFlowReversed())
                    bias = -bias;
                data.flickTarget =
                        -snapPosAt(-(dataValue - highlightRangeStart) + bias) + highlightRangeStart;
                maxDistance = qAbs(data.flickTarget - data.move.value());
                velocity = -maxVelocity;
            } else {
                maxDistance = qAbs(maxExtent - data.move.value());
            }
        }
        if (snapMode == QQuickListView::NoSnap && highlightRange != QQuickListView::StrictlyEnforceRange)
            data.flickTarget = maxExtent;
    }
    bool overShoot = boundsBehavior & QQuickFlickable::OvershootBounds;
    if (maxDistance > 0 || overShoot) {
        // These modes require the list to stop exactly on an item boundary.
        // The initial flick will estimate the boundary to stop on.
        // Since list items can have variable sizes, the boundary will be
        // reevaluated and adjusted as we approach the boundary.
        qreal v = velocity;
        if (maxVelocity != -1 && maxVelocity < qAbs(v)) {
            if (v < 0)
                v = -maxVelocity;
            else
                v = maxVelocity;
        }
        if (!hData.flicking && !vData.flicking) {
            // the initial flick - estimate boundary
            qreal accel = eventType == QEvent::Wheel ? wheelDeceleration : deceleration;
            qreal v2 = v * v;
            overshootDist = 0.0;
            // + averageSize/4 to encourage moving at least one item in the flick direction
            qreal dist = v2 / (accel * 2.0) + averageSize/4;
            if (maxDistance > 0)
                dist = qMin(dist, maxDistance);
            if (v > 0)
                dist = -dist;
            if ((maxDistance > 0.0 && v2 / (2.0f * maxDistance) < accel) || snapMode == QQuickListView::SnapOneItem) {
                if (snapMode != QQuickListView::SnapOneItem) {
                    qreal distTemp = isContentFlowReversed() ? -dist : dist;
                    data.flickTarget = -snapPosAt(-(dataValue - highlightRangeStart) + distTemp) + highlightRangeStart;
                }
                data.flickTarget = isContentFlowReversed() ? -data.flickTarget+size() : data.flickTarget;
                if (overShoot) {
                    if (data.flickTarget > minExtent) {
                        overshootDist = overShootDistance(vSize);
                        data.flickTarget += overshootDist;
                    } else if (data.flickTarget < maxExtent) {
                        overshootDist = overShootDistance(vSize);
                        data.flickTarget -= overshootDist;
                    }
                }
                qreal adjDist = -data.flickTarget + data.move.value();
                if (qAbs(adjDist) > qAbs(dist)) {
                    // Prevent painfully slow flicking - adjust velocity to suit flickDeceleration
                    qreal adjv2 = accel * 2.0f * qAbs(adjDist);
                    if (adjv2 > v2) {
                        v2 = adjv2;
                        v = qSqrt(v2);
                        if (dist > 0)
                            v = -v;
                    }
                }
                dist = adjDist;
                accel = v2 / (2.0f * qAbs(dist));
            } else if (overShoot) {
                data.flickTarget = data.move.value() - dist;
                if (data.flickTarget > minExtent) {
                    overshootDist = overShootDistance(vSize);
                    data.flickTarget += overshootDist;
                } else if (data.flickTarget < maxExtent) {
                    overshootDist = overShootDistance(vSize);
                    data.flickTarget -= overshootDist;
                }
            }
            timeline.reset(data.move);
            timeline.accel(data.move, v, accel, maxDistance + overshootDist);
            timeline.callback(QQuickTimeLineCallback(&data.move, fixupCallback, this));
            correctFlick = true;
            return true;
        } else {
            // reevaluate the target boundary.
            qreal newtarget = data.flickTarget;
            if (snapMode != QQuickListView::NoSnap || highlightRange == QQuickListView::StrictlyEnforceRange) {
                qreal tempFlickTarget = isContentFlowReversed() ? -data.flickTarget+size() : data.flickTarget;
                newtarget = -snapPosAt(-(tempFlickTarget - highlightRangeStart)) + highlightRangeStart;
                newtarget = isContentFlowReversed() ? -newtarget+size() : newtarget;
            }
            if (velocity < 0 && newtarget <= maxExtent)
                newtarget = maxExtent - overshootDist;
            else if (velocity > 0 && newtarget >= minExtent)
                newtarget = minExtent + overshootDist;
            if (newtarget == data.flickTarget) { // boundary unchanged - nothing to do
                if (qAbs(velocity) < _q_MinimumFlickVelocity)
                    correctFlick = false;
                return false;
            }
            data.flickTarget = newtarget;
            qreal dist = -newtarget + data.move.value();
            if ((v < 0 && dist < 0) || (v > 0 && dist > 0)) {
                correctFlick = false;
                timeline.reset(data.move);
                fixup(data, minExtent, maxExtent);
                return false;
            }
            timeline.reset(data.move);
            timeline.accelDistance(data.move, v, -dist);
            timeline.callback(QQuickTimeLineCallback(&data.move, fixupCallback, this));
            return false;
        }
    } else {
        correctFlick = false;
        timeline.reset(data.move);
        fixup(data, minExtent, maxExtent);
        return false;
    }
}
 
void QQuickListViewPrivate::setSectionHelper(QQmlContext *context, QQuickItem *sectionItem, const QString &section)
{
    // The section item can outlive its context
    // Skip the update rather than dereference the null context
    if (!context)
        return;
    if (!QQmlContextData::get(context)->isInternal() && context->contextProperty(QLatin1String("section")).isValid())
        context->setContextProperty(QLatin1String("section"), section);
    else
        sectionItem->setProperty("section", section);
}
 
QQuickItemViewAttached *QQuickListViewPrivate::getAttachedObject(const QObject *object) const
{
    QObject *attachedObject = qmlAttachedPropertiesObject<QQuickListView>(object);
    return static_cast<QQuickItemViewAttached *>(attachedObject);
}
 
//----------------------------------------------------------------------------
 
/*!
    \qmltype ListView
    \nativetype QQuickListView
    \inqmlmodule QtQuick
    \ingroup qtquick-views
    \inherits Flickable
    \brief Provides a list view of items provided by a model.
 
    A ListView displays data from models created from built-in QML types like ListModel
    and XmlListModel, or custom model classes defined in C++ that inherit from
    QAbstractItemModel or QAbstractListModel.
 
    A ListView has a \l model, which defines the data to be displayed, and
    a \l delegate, which defines how the data should be displayed. Items in a
    ListView are laid out horizontally or vertically. List views are inherently
    flickable because ListView inherits from \l Flickable.
 
    \note ListView will only load as many delegate items as needed to fill up the view.
    Items outside of the view will not be loaded unless a sufficient \l cacheBuffer has
    been set. Hence, a ListView with zero width or height might not load any delegate
    items at all.
 
    \section1 Example Usage
 
    The following example shows the definition of a simple list model defined
    in a file called \c ContactModel.qml:
 
    \snippet qml/listview/ContactModel.qml 0
 
    Another component can display this model data in a ListView, like this:
 
    \snippet qml/listview/listview.qml import
    \codeline
    \snippet qml/listview/listview.qml classdocs simple
 
    \image listview-simple.png {ListView showing three contacts with
           names and phone numbers}
 
    Here, the ListView creates a \c ContactModel component for its model, and a \l Text item
    for its delegate. The view will create a new \l Text component for each item in the model. Notice
    the delegate is able to access the model's \c name and \c number data directly.
 
    An improved list view is shown below. The delegate is visually improved and is moved
    into a separate \c contactDelegate component.
 
    \snippet qml/listview/listview.qml classdocs advanced
    \image listview-highlight.png {ListView with styled contact items
           and blue highlight on current selection}
 
    The currently selected item is highlighted with a blue \l Rectangle using the \l highlight property,
    and \c focus is set to \c true to enable keyboard navigation for the list view.
    The list view itself is a focus scope (see \l{Keyboard Focus in Qt Quick} for more details).
 
    Delegates are instantiated as needed and may be destroyed at any time.
    As such, \l {Avoid Storing State in Delegates}{state should \e never be stored in a delegate}.
    Delegates are usually parented to ListView's \l {Flickable::contentItem}{contentItem}, but
    typically depending on whether it's visible in the view or not, the \e parent
    can change, and sometimes be \c null. Because of that, binding to
    the parent's properties from within the delegate is \e not recommended. If you
    want the delegate to fill out the width of the ListView, consider
    using one of the following approaches instead:
 
    \code
    ListView {
        id: listView
        // ...
 
        delegate: Item {
            // Incorrect.
            width: parent.width
 
            // Correct.
            width: listView.width
            width: ListView.view.width
            // ...
        }
    }
    \endcode
 
    ListView attaches a number of properties to the root item of the delegate, for example
    \c ListView.isCurrentItem.  In the following example, the root delegate item can access
    this attached property directly as \c ListView.isCurrentItem, while the child
    \c contactInfo object must refer to this property as \c wrapper.ListView.isCurrentItem.
 
    \snippet qml/listview/listview.qml isCurrentItem
 
    \note Views do not enable \e clip automatically.  If the view
    is not clipped by another item or the screen, it will be necessary
    to set \e {clip: true} in order to have the out of view items clipped
    nicely.
 
 
    \section1 ListView Layouts
 
    The layout of the items in a ListView can be controlled by these properties:
 
    \list
    \li \l orientation - controls whether items flow horizontally or vertically.
        This value can be either Qt.Horizontal or Qt.Vertical.
    \li \l layoutDirection - controls the horizontal layout direction for a
        horizontally-oriented view: that is, whether items are laid out from the left side of
        the view to the right, or vice-versa. This value can be either Qt.LeftToRight or Qt.RightToLeft.
    \li \l verticalLayoutDirection - controls the vertical layout direction for a vertically-oriented
        view: that is, whether items are laid out from the top of the view down towards the bottom of
        the view, or vice-versa. This value can be either ListView.TopToBottom or ListView.BottomToTop.
    \endlist
 
    By default, a ListView has a vertical orientation, and items are laid out from top to bottom. The
    table below shows the different layouts that a ListView can have, depending on the values of
    the properties listed above.
 
    \table
    \header
        \li {2, 1}
            \b ListViews with Qt.Vertical orientation
    \row
        \li Top to bottom
            \image listview-layout-toptobottom.png {Vertical list with
                   items 0-4 arranged from top to bottom}
        \li Bottom to top
            \image listview-layout-bottomtotop.png {Vertical list with
                   items 0-4 arranged from bottom to top}
    \header
        \li {2, 1}
            \b ListViews with Qt.Horizontal orientation
    \row
        \li Left to right
            \image listview-layout-lefttoright.png {Horizontal list with
                   items 0-4 arranged from left to right}
        \li Right to left
            \image listview-layout-righttoleft.png {Horizontal list with
                   items 0-4 arranged from right to left}
    \endtable
 
    \section1 Flickable Direction
 
    By default, a vertical ListView sets \l {Flickable::}{flickableDirection} to \e Flickable.Vertical,
    and a horizontal ListView sets it to \e Flickable.Horizontal. Furthermore, a vertical ListView only
    calculates (estimates) the \l {Flickable::}{contentHeight}, and a horizontal ListView only calculates
    the \l {Flickable::}{contentWidth}. The other dimension is set to \e -1.
 
    Since Qt 5.9 (Qt Quick 2.9), it is possible to make a ListView that can be flicked to both directions.
    In order to do this, the \l {Flickable::}{flickableDirection} can be set to \e Flickable.AutoFlickDirection
    or \e Flickable.AutoFlickIfNeeded, and the desired \e contentWidth or \e contentHeight must be provided.
 
    \snippet qml/listview/listview.qml flickBothDirections
 
    \section1 Stacking Order in ListView
 
    The \l {QQuickItem::z}{Z value} of items determines whether they are
    rendered above or below other items. ListView uses several different
    default Z values, depending on what type of item is being created:
 
    \table
    \header
        \li Property
        \li Default Z value
    \row
        \li \l delegate
        \li 1
    \row
        \li \l footer
        \li 1
    \row
        \li \l header
        \li 1
    \row
        \li \l highlight
        \li 0
    \row
        \li \l section.delegate
        \li 2
    \endtable
 
    These default values are set if the Z value of the item is \c 0, so setting
    the Z value of these items to \c 0 has no effect. Note that the Z value is
    of type \l [QML] {real}, so it is possible to set fractional
    values like \c 0.1.
 
    \section1 Reusing Items
 
    Since 5.15, ListView can be configured to recycle items instead of instantiating
    from the \l delegate whenever new rows are flicked into view. This approach improves
    performance, depending on the complexity of the delegate. Reusing
    items is off by default (for backwards compatibility reasons), but can be switched
    on by setting the \l reuseItems property to \c true.
 
    When an item is flicked out, it moves to the \e{reuse pool}, which is an
    internal cache of unused items. When this happens, the \l ListView::pooled
    signal is emitted to inform the item about it. Likewise, when the item is
    moved back from the pool, the \l ListView::reused signal is emitted.
 
    Any item properties that come from the model are updated when the
    item is reused. This includes \c index and \c row, but also
    any model roles.
 
    \note \l {Avoid Storing State in Delegates}{Avoid storing any state inside
    a delegate}. If you do, reset it manually on receiving the
    \l ListView::reused signal.
 
    If an item has timers or animations, consider pausing them on receiving
    the \l ListView::pooled signal. That way you avoid using the CPU resources
    for items that are not visible. Likewise, if an item has resources that
    cannot be reused, they could be freed up.
 
    \note While an item is in the pool, it might still be alive and respond
    to connected signals and bindings.
 
    \note For an item to be pooled, it needs to be completely flicked out of the bounds
    of the view, \e including the extra margins set with \l {ListView::}{cacheBuffer}.
    Some items will also never be pooled or reused, such as \l currentItem.
 
    The following example shows a delegate that animates a spinning rectangle. When
    it is pooled, the animation is temporarily paused:
 
    \snippet qml/listview/ReusableDelegate.qml 0
 
    \sa {QML Data Models}, GridView, PathView, {Qt Quick Examples - Views}
 
    \section1 Variable Delegate Size and Section Labels
 
    Variable delegate sizes might lead to resizing and skipping of any attached
    \l {ScrollBar}. This is because ListView estimates its content size from
    allocated items (usually only the visible items, the rest are assumed to be of
    similar size), and variable delegate sizes prevent an accurate estimation. To
    reduce this effect, \l {ListView::}{cacheBuffer} can be set to higher values,
    effectively creating more items and improving the size estimate of unallocated
    items, at the expense of additional memory usage. \l{ListView::section}{Sections}
    have the same effect because they attach and elongate the section label to the
    first item within the section.
 
    \section1 Avoid Storing State in Delegates
 
    ListView's delegates are instantiated as needed and may be destroyed when
    out of view. For an illustration of this, run the following example:
 
    \snippet qml/listview/stateInDelegate.qml ListView
 
    When an item is clicked, \c channelActivated is set to \c true. However,
    because delegates can be \l {Reusing Items}{reused} and destroyed, all
    state is lost when the view is moved far enough. When the delegate becomes
    visible again, it will have its default, unmodified state (or, in the case
    of an item that was reused, old state from a previous item).
 
    To avoid this, state should be stored in the model:
 
    \snippet qml/listview/stateInModel.qml ListView
 
    \section1 Hiding Delegates
 
    Setting a delegate's \l {Item::}{visible} property to \c false will hide
    that item, but the space it occupied in the view will remain. It is
    possible to set the item's \l {Item::}{height} to \c 0 (for a \l
    {ListView::orientation}{vertical} ListView):
 
    \snippet qml/listview/hideDelegate.qml ListView
 
    Note that the hidden state is stored in the model, following the advice of
    the \l {Avoid Storing State in Delegates} section.
 
    However, if \l spacing is non-zero, there will be uneven gaps between
    delegates.
 
    A better option is to filter your model so that items that should not be
    visible are not loaded by the view at all. This can be achieved with
    \l QSortFilterProxyModel.
 
    Another option is to \l {Item::enabled}{disable} the delegate instead of
    hiding it.
*/
QQuickListView::QQuickListView(QQuickItem *parent)
    : QQuickItemView(*(new QQuickListViewPrivate), parent)
{
}
 
QQuickListView::~QQuickListView()
{
}
 
/*!
    \qmlattachedproperty bool QtQuick::ListView::isCurrentItem
    \readonly
 
    This attached property is true if this delegate is the current item; otherwise false.
 
    It is attached to each instance of the delegate.
 
    This property may be used to adjust the appearance of the current item, for example:
 
    \snippet qml/listview/listview.qml isCurrentItem
*/
 
/*!
    \qmlattachedproperty ListView QtQuick::ListView::view
    \readonly
 
    This attached property holds the view that manages this delegate instance.
 
    It is attached to each instance of the delegate and also to the header, the footer,
    the section and the highlight delegates.
*/
 
/*!
    \qmlattachedproperty string QtQuick::ListView::previousSection
    \readonly
 
    This attached property holds the section of the previous element.
 
    It is attached to each instance of the delegate.
 
    The section is evaluated using the \l {ListView::section.property}{section} properties.
*/
 
/*!
    \qmlattachedproperty string QtQuick::ListView::nextSection
    \readonly
 
    This attached property holds the section of the next element.
 
    It is attached to each instance of the delegate.
 
    The section is evaluated using the \l {ListView::section.property}{section} properties.
*/
 
/*!
    \qmlattachedproperty string QtQuick::ListView::section
    \readonly
 
    This attached property holds the section of this element.
 
    It is attached to each instance of the delegate.
 
    The section is evaluated using the \l {ListView::section.property}{section} properties.
*/
 
/*!
    \qmlattachedproperty bool QtQuick::ListView::delayRemove
 
    This attached property holds whether the delegate may be destroyed. It
    is attached to each instance of the delegate. The default value is false.
 
    It is sometimes necessary to delay the destruction of an item
    until an animation completes. The example delegate below ensures that the
    animation completes before the item is removed from the list.
 
    \snippet qml/listview/listview.qml delayRemove
 
    If a \l remove transition has been specified, it will not be applied until
    delayRemove is returned to \c false.
*/
 
/*!
    \qmlattachedsignal QtQuick::ListView::add()
    This attached signal is emitted immediately after an item is added to the view.
 
    If an \l add transition is specified, it is applied immediately after
    this signal is handled.
*/
 
/*!
    \qmlattachedsignal QtQuick::ListView::remove()
    This attached signal is emitted immediately before an item is removed from the view.
 
    If a \l remove transition has been specified, it is applied after
    this signal is handled, providing that \l delayRemove is false.
*/
 
/*!
    \qmlproperty model QtQuick::ListView::model
    This property holds the model providing data for the list.
 
    The model provides the set of data that is used to create the items
    in the view. Models can be created directly in QML using \l ListModel,
    \l ObjectModel, or provided by C++ model classes. If a C++ model class is
    used, it must be a subclass of \l QAbstractItemModel or a simple list.
 
    \sa {qml-data-models}{Data Models}
*/
 
/*!
    \qmlproperty Component QtQuick::ListView::delegate
 
    The delegate provides a template defining each item instantiated by the view.
    The index is exposed as an accessible \c index property.  Properties of the
    model are also available depending upon the type of \l {qml-data-models}{Data Model}.
 
    The number of objects and bindings in the delegate has a direct effect on the
    flicking performance of the view.  If at all possible, place functionality
    that is not needed for the normal display of the delegate in a \l Loader which
    can load additional components when needed.
 
    The ListView will lay out the items based on the size of the root item
    in the delegate.
 
    It is recommended that the delegate's size be a whole number to avoid sub-pixel
    alignment of items.
 
    The default \l {QQuickItem::z}{stacking order} of delegate instances is \c 1.
 
    \note Delegates are instantiated as needed and may be destroyed at any time.
    They are parented to ListView's \l {Flickable::contentItem}{contentItem}, not to the view itself.
    State should \e never be stored in a delegate.
 
    \sa {Stacking Order in ListView}
*/
 
/*!
    \qmlproperty enumeration QtQuick::ListView::delegateModelAccess
    \since 6.10
 
    \include delegatemodelaccess.qdocinc
*/
 
/*!
    \qmlproperty int QtQuick::ListView::currentIndex
    \qmlproperty Item QtQuick::ListView::currentItem
 
    The \c currentIndex property holds the index of the current item, and
    \c currentItem holds the current item.   Setting the currentIndex to -1
    will clear the highlight and set currentItem to null.
 
    If highlightFollowsCurrentItem is \c true, setting either of these
    properties will smoothly scroll the ListView so that the current
    item becomes visible.
 
    Note that the position of the current item
    may only be approximate until it becomes visible in the view.
 
    As \c currentItem needs to work with any delegate, its type is \l{Item}.
    Often, a \c ListView is however used with exactly one type of delegate.
    In that case, casting \c currentItem to the delegate's type can help
    tooling and lead to more efficient code:
 
    \qml
    component Message : Item {
        required property string sender
        required property string text
    }
    ListView {
        id: messageView
        delegate: Message {}
        model: messageModel
    }
    Button {
        text: "Reply to %1".arg((messageView.currentItem) as Message).sender
    }
    \endqml
*/
 
/*!
  \qmlproperty Item QtQuick::ListView::highlightItem
 
    This holds the highlight item created from the \l highlight component.
 
  The \c highlightItem is managed by the view unless
  \l highlightFollowsCurrentItem is set to false.
  The default \l {QQuickItem::z}{stacking order}
  of the highlight item is \c 0.
 
  \sa highlight, highlightFollowsCurrentItem, {Stacking Order in ListView}
*/
 
/*!
  \qmlproperty int QtQuick::ListView::count
    The property reflects the number of items in the \l ListView's model,
    regardless of whether they are visible or instantiated as \c Item of a delegate component.
*/
 
/*!
    \qmlproperty bool QtQuick::ListView::reuseItems
 
    This property enables you to reuse items that are instantiated
    from the \l delegate. If set to \c false, any currently
    pooled items are destroyed.
 
    This property is \c false by default.
 
    \since 5.15
 
    \sa {Reusing items}, pooled(), reused()
*/
 
/*!
    \qmlattachedsignal QtQuick::ListView::pooled()
 
    This signal is emitted after an item has been added to the reuse
    pool. You can use it to pause ongoing timers or animations inside
    the item, or free up resources that cannot be reused.
 
    This signal is emitted only if the \l reuseItems property is \c true.
 
    \sa {Reusing items}, reuseItems, reused()
*/
 
/*!
    \qmlattachedsignal QtQuick::ListView::reused()
 
    This signal is emitted after an item has been reused. At this point, the
    item has been taken out of the pool and placed inside the content view,
    and the model properties such as \c index and \c row have been updated.
 
    Other properties that are not provided by the model does not change when an
    item is reused. You should avoid storing any state inside a delegate, but if
    you do, manually reset that state on receiving this signal.
 
    This signal is emitted when the item is reused, and not the first time the
    item is created.
 
    This signal is emitted only if the \l reuseItems property is \c true.
 
    \sa {Reusing items}, reuseItems, pooled()
*/
 
/*!
    \qmlproperty Component QtQuick::ListView::highlight
    This property holds the component to use as the highlight.
 
    An instance of the highlight component is created for each list.
    The geometry of the resulting component instance is managed by the list
    so as to stay with the current item, unless the highlightFollowsCurrentItem
    property is false. The default \l {QQuickItem::z}{stacking order} of the
    highlight item is \c 0.
 
    \sa highlightItem, highlightFollowsCurrentItem,
    {Qt Quick Examples - Views#Using Highlight}{ListView Highlight Example},
    {Stacking Order in ListView}
*/
 
/*!
    \qmlproperty bool QtQuick::ListView::highlightFollowsCurrentItem
    This property holds whether the highlight is managed by the view.
 
    If this property is true (the default value), the highlight is moved smoothly
    to follow the current item.  Otherwise, the
    highlight is not moved by the view, and any movement must be implemented
    by the highlight.
 
    Here is a highlight with its motion defined by a \l {SpringAnimation} item:
 
    \snippet qml/listview/listview.qml highlightFollowsCurrentItem
 
    Note that the highlight animation also affects the way that the view
    is scrolled.  This is because the view moves to maintain the
    highlight within the preferred highlight range (or visible viewport).
 
    \sa highlight, highlightMoveVelocity
*/
//###Possibly rename these properties, since they are very useful even without a highlight?
/*!
    \qmlproperty real QtQuick::ListView::preferredHighlightBegin
    \qmlproperty real QtQuick::ListView::preferredHighlightEnd
    \qmlproperty enumeration QtQuick::ListView::highlightRangeMode
 
    These properties define the preferred range of the highlight (for the current item)
    within the view. The \c preferredHighlightBegin value must be less than the
    \c preferredHighlightEnd value.
 
    These properties affect the position of the current item when the list is scrolled.
    For example, if the currently selected item should stay in the middle of the
    list when the view is scrolled, set the \c preferredHighlightBegin and
    \c preferredHighlightEnd values to the top and bottom coordinates of where the middle
    item would be. If the \c currentItem is changed programmatically, the list will
    automatically scroll so that the current item is in the middle of the view.
    Furthermore, the behavior of the current item index will occur whether or not a
    highlight exists.
 
    Valid values for \c highlightRangeMode are:
 
    \value ListView.ApplyRange              the view attempts to maintain the highlight within the range.
                                            However, the highlight can move outside of the range at the
                                            ends of the list or due to mouse interaction.
    \value ListView.StrictlyEnforceRange    the highlight never moves outside of the range.
                                            The current item changes if a keyboard or mouse action would
                                            cause the highlight to move outside of the range.
    \value ListView.NoHighlightRange        this is the default value.
*/
void QQuickListView::setHighlightFollowsCurrentItem(bool autoHighlight)
{
    Q_D(QQuickListView);
    if (d->autoHighlight != autoHighlight) {
        if (!autoHighlight) {
            if (d->highlightPosAnimator)
                d->highlightPosAnimator->stop();
            if (d->highlightWidthAnimator)
                d->highlightWidthAnimator->stop();
            if (d->highlightHeightAnimator)
                d->highlightHeightAnimator->stop();
        }
        QQuickItemView::setHighlightFollowsCurrentItem(autoHighlight);
    }
}
 
/*!
    \qmlproperty real QtQuick::ListView::spacing
 
    This property holds the spacing between items.
 
    The default value is 0.
*/
qreal QQuickListView::spacing() const
{
    Q_D(const QQuickListView);
    return d->spacing;
}
 
void QQuickListView::setSpacing(qreal spacing)
{
    Q_D(QQuickListView);
    if (spacing != d->spacing) {
        d->spacing = spacing;
        d->forceLayoutPolish();
        emit spacingChanged();
    }
}
 
/*!
    \qmlproperty enumeration QtQuick::ListView::orientation
    This property holds the orientation of the list.
 
    Possible values:
 
    \value ListView.Horizontal  Items are laid out horizontally
    \br
    \inlineimage ListViewHorizontal.png
        {Three contact cards arranged horizontally: Bill Smith, John Brown, Sam Wise}
    \value ListView.Vertical    (default) Items are laid out vertically
    \br
    \inlineimage listview-highlight.png
        {Three contact cards stacked vertically: Bill Smith, John Brown, Sam Wise}
 
    \sa {Flickable Direction}
*/
QQuickListView::Orientation QQuickListView::orientation() const
{
    Q_D(const QQuickListView);
    return d->orient;
}
 
void QQuickListView::setOrientation(QQuickListView::Orientation orientation)
{
    Q_D(QQuickListView);
    if (d->orient != orientation) {
        d->orient = orientation;
        if (d->orient == Vertical) {
            if (d->flickableDirection == HorizontalFlick) {
                setFlickableDirection(VerticalFlick);
                if (isComponentComplete())
                    setContentWidth(-1);
            }
            setContentX(0);
        } else {
            if (d->flickableDirection == VerticalFlick) {
                setFlickableDirection(HorizontalFlick);
                if (isComponentComplete())
                    setContentHeight(-1);
            }
            setContentY(0);
        }
        d->regenerate(true);
        emit orientationChanged();
    }
}
 
/*!
  \qmlproperty enumeration QtQuick::ListView::layoutDirection
  This property holds the layout direction of a horizontally-oriented list.
 
  Possible values:
 
  \value Qt.LeftToRight (default) Items will be laid out from left to right.
  \value Qt.RightToLeft Items will be laid out from right to left.
 
  Setting this property has no effect if the \l orientation is Qt.Vertical.
 
  \sa ListView::effectiveLayoutDirection, ListView::verticalLayoutDirection
*/
 
 
/*!
    \qmlproperty enumeration QtQuick::ListView::effectiveLayoutDirection
    This property holds the effective layout direction of a horizontally-oriented list.
 
    When using the attached property \l {LayoutMirroring::enabled}{LayoutMirroring::enabled} for locale layouts,
    the visual layout direction of the horizontal list will be mirrored. However, the
    property \l {ListView::layoutDirection}{layoutDirection} will remain unchanged.
 
    \sa ListView::layoutDirection, {LayoutMirroring}{LayoutMirroring}
*/
 
 
/*!
  \qmlproperty enumeration QtQuick::ListView::verticalLayoutDirection
  This property holds the layout direction of a vertically-oriented list.
 
  Possible values:
 
  \value ListView.TopToBottom   (default) Items are laid out from the top of the view down to the bottom of the view.
  \value ListView.BottomToTop   Items are laid out from the bottom of the view up to the top of the view.
 
  Setting this property has no effect if the \l orientation is Qt.Horizontal.
 
  \sa ListView::layoutDirection
*/
 
 
/*!
    \qmlproperty bool QtQuick::ListView::keyNavigationWraps
    This property holds whether the list wraps key navigation.
 
    If this is true, key navigation that would move the current item selection
    past the end of the list instead wraps around and moves the selection to
    the start of the list, and vice-versa.
 
    By default, key navigation is not wrapped.
*/
 
/*!
    \qmlproperty bool QtQuick::ListView::keyNavigationEnabled
    \since 5.7
 
    This property holds whether the key navigation of the list is enabled.
 
    If this is \c true, the user can navigate the view with a keyboard.
    It is useful for applications that need to selectively enable or
    disable mouse and keyboard interaction.
 
    By default, the value of this property is bound to
    \l {Flickable::}{interactive} to ensure behavior compatibility for
    existing applications. When explicitly set, it will cease to be bound to
    the interactive property.
 
    \sa {Flickable::}{interactive}
*/
 
 
/*!
    \qmlproperty int QtQuick::ListView::cacheBuffer
    This property determines whether delegates are retained outside the
    visible area of the view.
 
    If this value is greater than zero, the view may keep as many delegates
    instantiated as it can fit within the buffer specified.  For example,
    if in a vertical view the delegate is 20 pixels high and \c cacheBuffer is
    set to 40, then up to 2 delegates above and 2 delegates below the visible
    area may be created/retained.  The buffered delegates are created asynchronously,
    allowing creation to occur across multiple frames and reducing the
    likelihood of skipping frames.  In order to improve painting performance
    delegates outside the visible area are not painted.
 
    The default value of this property is platform dependent, but will usually
    be a value greater than zero. Negative values are ignored.
 
    Note that cacheBuffer is not a pixel buffer - it only maintains additional
    instantiated delegates.
 
    \note Setting this property is not a replacement for creating efficient delegates.
    It can improve the smoothness of scrolling behavior at the expense of additional
    memory usage. The fewer objects and bindings in a delegate, the faster a
    view can be scrolled. It is important to realize that setting a cacheBuffer
    will only postpone issues caused by slow-loading delegates, it is not a
    solution for this scenario.
 
    The cacheBuffer operates outside of any display margins specified by
    displayMarginBeginning or displayMarginEnd.
*/
 
/*!
    \qmlproperty int QtQuick::ListView::displayMarginBeginning
    \qmlproperty int QtQuick::ListView::displayMarginEnd
    \since QtQuick 2.3
 
    This property allows delegates to be displayed outside of the view geometry.
 
    If this value is non-zero, the view will create extra delegates before the
    start of the view, or after the end. The view will create as many delegates
    as it can fit into the pixel size specified.
 
    For example, if in a vertical view the delegate is 20 pixels high and
    \c displayMarginBeginning and \c displayMarginEnd are both set to 40,
    then 2 delegates above and 2 delegates below will be created and shown.
 
    The default value is 0.
 
    This property is meant for allowing certain UI configurations,
    and not as a performance optimization. If you wish to create delegates
    outside of the view geometry for performance reasons, you probably
    want to use the cacheBuffer property instead.
*/
 
/*!
    \qmlpropertygroup QtQuick::ListView::section
    \qmlproperty string QtQuick::ListView::section.property
    \qmlproperty enumeration QtQuick::ListView::section.criteria
    \qmlproperty Component QtQuick::ListView::section.delegate
    \qmlproperty enumeration QtQuick::ListView::section.labelPositioning
 
    These properties determine the expression to be evaluated and appearance
    of the section labels.
 
    \c section.property holds the name of the property that is the basis
    of each section.
 
    \c section.criteria holds the criteria for forming each section based on
    \c section.property. This value can be one of:
 
    \value ViewSection.FullString       (default) sections are created based on the
                                        \c section.property value.
    \value ViewSection.FirstCharacter   sections are created based on the first character of
                                        the \c section.property value (for example,
                                        'A', 'B', 'C' ... sections for an address book.)
 
    A case insensitive comparison is used when determining section
    boundaries.
 
    \c section.delegate holds the delegate component for each section. The
    default \l {QQuickItem::z}{stacking order} of section delegate instances
    is \c 2. If you declare a \c required property named "section" in it,
    that property will contain the section's title.
 
    \c section.labelPositioning determines whether the current and/or
    next section labels stick to the start/end of the view, and whether
    the labels are shown inline.  This value can be a combination of:
 
    \value ViewSection.InlineLabels
        (default) section labels are shown inline between the item delegates
        separating sections.
    \value ViewSection.CurrentLabelAtStart
        the current section label sticks to the start of the view as it is moved.
    \value ViewSection.NextLabelAtEnd
        the next section label (beyond all visible sections) sticks to the end
        of the view as it is moved.
        \note Enabling \c ViewSection.NextLabelAtEnd requires the view to scan
        ahead for the next section, which has performance implications,
        especially for slower models.
 
    Each item in the list has attached properties named \c ListView.section,
    \c ListView.previousSection and \c ListView.nextSection.
 
    For example, here is a ListView that displays a list of animals, separated
    into sections. Each item in the ListView is placed in a different section
    depending on the "size" property of the model item. The \c sectionHeading
    delegate component provides the light blue bar that marks the beginning of
    each section.
 
 
    \snippet views/listview/sections.qml 0
 
    \image qml-listview-sections-example.png {ListView with items grouped
           into sections with light blue header bars}
 
    \note Adding sections to a ListView does not automatically re-order the
    list items by the section criteria.
    If the model is not ordered by section, then it is possible that
    the sections created will not be unique; each boundary between
    differing sections will result in a section header being created
    even if that section exists elsewhere.
 
    \sa {Qt Quick Examples - Views}{ListView examples},
    {Stacking Order in ListView}
*/
QQuickViewSection *QQuickListView::sectionCriteria()
{
    Q_D(QQuickListView);
    if (!d->sectionCriteria)
        d->sectionCriteria = new QQuickViewSection(this);
    return d->sectionCriteria;
}
 
/*!
    \qmlproperty string QtQuick::ListView::currentSection
    This property holds the section that is currently at the beginning of the view.
*/
QString QQuickListView::currentSection() const
{
    Q_D(const QQuickListView);
    return d->currentSection;
}
 
/*!
    \qmlproperty real QtQuick::ListView::highlightMoveVelocity
    \qmlproperty int QtQuick::ListView::highlightMoveDuration
    \qmlproperty real QtQuick::ListView::highlightResizeVelocity
    \qmlproperty int QtQuick::ListView::highlightResizeDuration
 
    These properties control the speed of the move and resize animations for the
    highlight delegate.
 
    \l highlightFollowsCurrentItem must be true for these properties
    to have effect.
 
    The default value for the velocity properties is 400 pixels/second.
    The default value for the duration properties is -1, i.e. the
    highlight will take as much time as necessary to move at the set speed.
 
    These properties have the same characteristics as a SmoothedAnimation:
    if both the velocity and duration are set, the animation will use
    whichever gives the shorter duration.
 
    The move velocity and duration properties are used to control movement due
    to index changes; for example, when incrementCurrentIndex() is called. When
    the user flicks a ListView, the velocity from the flick is used to control
    the movement instead.
 
    To set only one property, the other can be set to \c -1. For example,
    if you only want to animate the duration and not velocity, use the
    following code:
 
    \code
    highlightMoveDuration: 1000
    highlightMoveVelocity: -1
    \endcode
 
    \sa highlightFollowsCurrentItem
*/
qreal QQuickListView::highlightMoveVelocity() const
{
    Q_D(const QQuickListView);
    return d->highlightMoveVelocity;
}
 
void QQuickListView::setHighlightMoveVelocity(qreal speed)
{
    Q_D(QQuickListView);
    if (d->highlightMoveVelocity != speed) {
        d->highlightMoveVelocity = speed;
        if (d->highlightPosAnimator)
            d->highlightPosAnimator->velocity = d->highlightMoveVelocity;
        emit highlightMoveVelocityChanged();
    }
}
 
void QQuickListView::setHighlightMoveDuration(int duration)
{
    Q_D(QQuickListView);
    if (d->highlightMoveDuration != duration) {
        if (d->highlightPosAnimator)
            d->highlightPosAnimator->userDuration = duration;
        QQuickItemView::setHighlightMoveDuration(duration);
    }
}
 
qreal QQuickListView::highlightResizeVelocity() const
{
    Q_D(const QQuickListView);
    return d->highlightResizeVelocity;
}
 
void QQuickListView::setHighlightResizeVelocity(qreal speed)
{
    Q_D(QQuickListView);
    if (d->highlightResizeVelocity != speed) {
        d->highlightResizeVelocity = speed;
        if (d->highlightWidthAnimator)
            d->highlightWidthAnimator->velocity = d->highlightResizeVelocity;
        if (d->highlightHeightAnimator)
            d->highlightHeightAnimator->velocity = d->highlightResizeVelocity;
        emit highlightResizeVelocityChanged();
    }
}
 
int QQuickListView::highlightResizeDuration() const
{
    Q_D(const QQuickListView);
    return d->highlightResizeDuration;
}
 
void QQuickListView::setHighlightResizeDuration(int duration)
{
    Q_D(QQuickListView);
    if (d->highlightResizeDuration != duration) {
        d->highlightResizeDuration = duration;
        if (d->highlightWidthAnimator)
            d->highlightWidthAnimator->userDuration = d->highlightResizeDuration;
        if (d->highlightHeightAnimator)
            d->highlightHeightAnimator->userDuration = d->highlightResizeDuration;
        emit highlightResizeDurationChanged();
    }
}
 
/*!
    \qmlproperty enumeration QtQuick::ListView::snapMode
 
    This property determines how the view scrolling will settle following a drag or flick.
    The possible values are:
 
    \value ListView.NoSnap      (default) the view stops anywhere within the visible area.
    \value ListView.SnapToItem  the view settles with an item aligned with the start of the view.
    \value ListView.SnapOneItem the view settles no more than one item away from the first
        visible item at the time the mouse button is released.  This mode is particularly
        useful for moving one page at a time. When SnapOneItem is enabled, the ListView will
        show a stronger affinity to neighboring items when movement occurs. For example, a
        short drag that snaps back to the current item with SnapToItem might snap to a
        neighboring item with SnapOneItem.
 
    \c snapMode does not affect the \l currentIndex.  To update the
    \l currentIndex as the list is moved, set \l highlightRangeMode
    to \c ListView.StrictlyEnforceRange.
 
    \sa highlightRangeMode
*/
QQuickListView::SnapMode QQuickListView::snapMode() const
{
    Q_D(const QQuickListView);
    return d->snapMode;
}
 
void QQuickListView::setSnapMode(SnapMode mode)
{
    Q_D(QQuickListView);
    if (d->snapMode != mode) {
        d->snapMode = mode;
        emit snapModeChanged();
        d->fixupPosition();
    }
}
 
 
/*!
    \qmlproperty Component QtQuick::ListView::footer
    This property holds the component to use as the footer.
 
    An instance of the footer component is created for each view.  The
    footer is positioned at the end of the view, after any items. The
    default \l {QQuickItem::z}{stacking order} of the footer is \c 1.
 
    \sa header, footerItem, {Stacking Order in ListView}
*/
 
 
/*!
    \qmlproperty Component QtQuick::ListView::header
    This property holds the component to use as the header.
 
    An instance of the header component is created for each view.  The
    header is positioned at the beginning of the view, before any items.
    The default \l {QQuickItem::z}{stacking order} of the header is \c 1.
 
    \sa footer, headerItem, {Stacking Order in ListView}
*/
 
/*!
    \qmlproperty Item QtQuick::ListView::headerItem
    This holds the header item created from the \l header component.
 
    An instance of the header component is created for each view.  The
    header is positioned at the beginning of the view, before any items.
    The default \l {QQuickItem::z}{stacking order} of the header is \c 1.
 
    \sa header, footerItem, {Stacking Order in ListView}
*/
 
/*!
    \qmlproperty Item QtQuick::ListView::footerItem
    This holds the footer item created from the \l footer component.
 
    An instance of the footer component is created for each view.  The
    footer is positioned at the end of the view, after any items. The
    default \l {QQuickItem::z}{stacking order} of the footer is \c 1.
 
    \sa footer, headerItem, {Stacking Order in ListView}
*/
 
/*!
    \qmlproperty enumeration QtQuick::ListView::headerPositioning
    \since Qt 5.4
 
    This property determines the positioning of the \l{headerItem}{header item}.
 
    \value ListView.InlineHeader (default) The header is positioned at the beginning
    of the content and moves together with the content like an ordinary item.
 
    \value ListView.OverlayHeader  The header is positioned at the beginning of the view.
 
    \value ListView.PullBackHeader The header is positioned at the beginning of the view.
    The header can be pushed away by moving the content forwards, and pulled back by
    moving the content backwards.
 
    \note This property has no effect on the \l {QQuickItem::z}{stacking order}
    of the header. For example, if the header should be shown above the
    \l delegate items when using \c ListView.OverlayHeader, its Z value
    should be set to a value higher than that of the delegates. For more
    information, see \l {Stacking Order in ListView}.
 
    \note If \c headerPositioning is not set to \c ListView.InlineHeader, the
    user cannot press and flick the list from the header. In any case, the
    \l{headerItem}{header item} may contain items or event handlers that
    provide custom handling of mouse or touch input.
*/
QQuickListView::HeaderPositioning QQuickListView::headerPositioning() const
{
    Q_D(const QQuickListView);
    return d->headerPositioning;
}
 
void QQuickListView::setHeaderPositioning(QQuickListView::HeaderPositioning positioning)
{
    Q_D(QQuickListView);
    if (d->headerPositioning != positioning) {
        d->applyPendingChanges();
        d->headerPositioning = positioning;
        if (isComponentComplete()) {
            d->updateHeader();
            d->updateViewport();
            d->fixupPosition();
        }
        emit headerPositioningChanged();
    }
}
 
/*!
    \qmlproperty enumeration QtQuick::ListView::footerPositioning
    \since Qt 5.4
 
    This property determines the positioning of the \l{footerItem}{footer item}.
 
    \value ListView.InlineFooter (default) The footer is positioned at the end
    of the content and moves together with the content like an ordinary item.
 
    \value ListView.OverlayFooter The footer is positioned at the end of the view.
 
    \value ListView.PullBackFooter The footer is positioned at the end of the view.
    The footer can be pushed away by moving the content backwards, and pulled back by
    moving the content forwards.
 
    \note This property has no effect on the \l {QQuickItem::z}{stacking order}
    of the footer. For example, if the footer should be shown above the
    \l delegate items when using \c ListView.OverlayFooter, its Z value
    should be set to a value higher than that of the delegates. For more
    information, see \l {Stacking Order in ListView}.
 
    \note If \c footerPositioning is not set to \c ListView.InlineFooter, the
    user cannot press and flick the list from the footer. In any case, the
    \l{footerItem}{footer item} may contain items or event handlers that
    provide custom handling of mouse or touch input.
*/
QQuickListView::FooterPositioning QQuickListView::footerPositioning() const
{
    Q_D(const QQuickListView);
    return d->footerPositioning;
}
 
void QQuickListView::setFooterPositioning(QQuickListView::FooterPositioning positioning)
{
    Q_D(QQuickListView);
    if (d->footerPositioning != positioning) {
        d->applyPendingChanges();
        d->footerPositioning = positioning;
        if (isComponentComplete()) {
            d->updateFooter();
            d->updateViewport();
            d->fixupPosition();
        }
        emit footerPositioningChanged();
    }
}
 
/*!
    \qmlproperty Transition QtQuick::ListView::populate
 
    This property holds the transition to apply to the items that are initially created
    for a view.
 
    It is applied to all items that are created when:
 
    \list
    \li The view is first created
    \li The view's \l model changes in such a way that the visible delegates are completely replaced
    \li The view's \l model is \l {QAbstractItemModel::beginResetModel()}{reset}, if the model is a
        QAbstractItemModel subclass
    \endlist
 
    For example, here is a view that specifies such a transition:
 
    \code
    ListView {
        ...
        populate: Transition {
            NumberAnimation { properties: "x,y"; duration: 1000 }
        }
    }
    \endcode
 
    When the view is initialized, the view will create all the necessary items for the view,
    then animate them to their correct positions within the view over one second.
 
    However when scrolling the view later, the populate transition does not
    run, even though delegates are being instantiated as they become visible.
    When the model changes in a way that new delegates become visible, the
    \l add transition is the one that runs. So you should not depend on the
    \c populate transition to initialize properties in the delegate, because it
    does not apply to every delegate. If your animation sets the \c to value of
    a property, the property should initially have the \c to value, and the
    animation should set the \c from value in case it is animated:
 
    \code
    ListView {
        ...
        delegate: Rectangle {
            opacity: 1 // not necessary because it's the default
        }
        populate: Transition {
            NumberAnimation { property: "opacity"; from: 0; to: 1; duration: 1000 }
        }
    }
    \endcode
 
    For more details and examples on how to use view transitions, see the ViewTransition
    documentation.
 
    \sa add, ViewTransition
*/
 
/*!
    \qmlproperty Transition QtQuick::ListView::add
 
    This property holds the transition to apply to items that are added to the view.
 
    For example, here is a view that specifies such a transition:
 
    \code
    ListView {
        ...
        add: Transition {
            NumberAnimation { properties: "x,y"; from: 100; duration: 1000 }
        }
    }
    \endcode
 
    Whenever an item is added to the above view, the item will be animated from the position (100,100)
    to its final x,y position within the view, over one second. The transition only applies to
    the new items that are added to the view; it does not apply to the items below that are
    displaced by the addition of the new items. To animate the displaced items, set the \l displaced
    or \l addDisplaced properties.
 
    For more details and examples on how to use view transitions, see the ViewTransition
    documentation.
 
    \note This transition is not applied to the items that are created when the view is initially
    populated, or when the view's \l model changes. (In those cases, the \l populate transition is
    applied instead.) Additionally, this transition should \e not animate the height of the new item;
    doing so will cause any items beneath the new item to be laid out at the wrong position. Instead,
    the height can be animated within the \l {add}{onAdd} handler in the delegate.
 
    \sa addDisplaced, populate, ViewTransition
*/
 
/*!
    \qmlproperty Transition QtQuick::ListView::addDisplaced
 
    This property holds the transition to apply to items within the view that are displaced by
    the addition of other items to the view.
 
    For example, here is a view that specifies such a transition:
 
    \code
    ListView {
        ...
        addDisplaced: Transition {
            NumberAnimation { properties: "x,y"; duration: 1000 }
        }
    }
    \endcode
 
    Whenever an item is added to the above view, all items beneath the new item are displaced, causing
    them to move down (or sideways, if horizontally orientated) within the view. As this
    displacement occurs, the items' movement to their new x,y positions within the view will be
    animated by a NumberAnimation over one second, as specified. This transition is not applied to
    the new item that has been added to the view; to animate the added items, set the \l add
    property.
 
    If an item is displaced by multiple types of operations at the same time, it is not defined as to
    whether the addDisplaced, moveDisplaced or removeDisplaced transition will be applied. Additionally,
    if it is not necessary to specify different transitions depending on whether an item is displaced
    by an add, move or remove operation, consider setting the \l displaced property instead.
 
    For more details and examples on how to use view transitions, see the ViewTransition
    documentation.
 
    \note This transition is not applied to the items that are created when the view is initially
    populated, or when the view's \l model changes. In those cases, the \l populate transition is
    applied instead.
 
    \sa displaced, add, populate, ViewTransition
*/
 
/*!
    \qmlproperty Transition QtQuick::ListView::move
 
    This property holds the transition to apply to items in the view that are being moved due
    to a move operation in the view's \l model.
 
    For example, here is a view that specifies such a transition:
 
    \code
    ListView {
        ...
        move: Transition {
            NumberAnimation { properties: "x,y"; duration: 1000 }
        }
    }
    \endcode
 
    Whenever the \l model performs a move operation to move a particular set of indexes, the
    respective items in the view will be animated to their new positions in the view over one
    second. The transition only applies to the items that are the subject of the move operation
    in the model; it does not apply to items below them that are displaced by the move operation.
    To animate the displaced items, set the \l displaced or \l moveDisplaced properties.
 
    For more details and examples on how to use view transitions, see the ViewTransition
    documentation.
 
    \sa moveDisplaced, ViewTransition
*/
 
/*!
    \qmlproperty Transition QtQuick::ListView::moveDisplaced
 
    This property holds the transition to apply to items that are displaced by a move operation in
    the view's \l model.
 
    For example, here is a view that specifies such a transition:
 
    \code
    ListView {
        ...
        moveDisplaced: Transition {
            NumberAnimation { properties: "x,y"; duration: 1000 }
        }
    }
    \endcode
 
    Whenever the \l model performs a move operation to move a particular set of indexes, the items
    between the source and destination indexes of the move operation are displaced, causing them
    to move upwards or downwards (or sideways, if horizontally orientated) within the view. As this
    displacement occurs, the items' movement to their new x,y positions within the view will be
    animated by a NumberAnimation over one second, as specified. This transition is not applied to
    the items that are the actual subjects of the move operation; to animate the moved items, set
    the \l move property.
 
    If an item is displaced by multiple types of operations at the same time, it is not defined as to
    whether the addDisplaced, moveDisplaced or removeDisplaced transition will be applied. Additionally,
    if it is not necessary to specify different transitions depending on whether an item is displaced
    by an add, move or remove operation, consider setting the \l displaced property instead.
 
    For more details and examples on how to use view transitions, see the ViewTransition
    documentation.
 
    \sa displaced, move, ViewTransition
*/
 
/*!
    \qmlproperty Transition QtQuick::ListView::remove
 
    This property holds the transition to apply to items that are removed from the view.
 
    For example, here is a view that specifies such a transition:
 
    \code
    ListView {
        ...
        remove: Transition {
            ParallelAnimation {
                NumberAnimation { property: "opacity"; to: 0; duration: 1000 }
                NumberAnimation { properties: "x,y"; to: 100; duration: 1000 }
            }
        }
    }
    \endcode
 
    Whenever an item is removed from the above view, the item will be animated to the position (100,100)
    over one second, and in parallel will also change its opacity to 0. The transition
    only applies to the items that are removed from the view; it does not apply to the items below
    them that are displaced by the removal of the items. To animate the displaced items, set the
    \l displaced or \l removeDisplaced properties.
 
    Note that by the time the transition is applied, the item has already been removed from the
    model; any references to the model data for the removed index will not be valid.
 
    Additionally, if the \l delayRemove attached property has been set for a delegate item, the
    remove transition will not be applied until \l delayRemove becomes false again.
 
    For more details and examples on how to use view transitions, see the ViewTransition
    documentation.
 
    \sa removeDisplaced, ViewTransition
*/
 
/*!
    \qmlproperty Transition QtQuick::ListView::removeDisplaced
 
    This property holds the transition to apply to items in the view that are displaced by the
    removal of other items in the view.
 
    For example, here is a view that specifies such a transition:
 
    \code
    ListView {
        ...
        removeDisplaced: Transition {
            NumberAnimation { properties: "x,y"; duration: 1000 }
        }
    }
    \endcode
 
    Whenever an item is removed from the above view, all items beneath it are displaced, causing
    them to move upwards (or sideways, if horizontally orientated) within the view. As this
    displacement occurs, the items' movement to their new x,y positions within the view will be
    animated by a NumberAnimation over one second, as specified. This transition is not applied to
    the item that has actually been removed from the view; to animate the removed items, set the
    \l remove property.
 
    If an item is displaced by multiple types of operations at the same time, it is not defined as to
    whether the addDisplaced, moveDisplaced or removeDisplaced transition will be applied. Additionally,
    if it is not necessary to specify different transitions depending on whether an item is displaced
    by an add, move or remove operation, consider setting the \l displaced property instead.
 
    For more details and examples on how to use view transitions, see the ViewTransition
    documentation.
 
    \sa displaced, remove, ViewTransition
*/
 
/*!
    \qmlproperty Transition QtQuick::ListView::displaced
    This property holds the generic transition to apply to items that have been displaced by
    any model operation that affects the view.
 
    This is a convenience for specifying the generic transition to be applied to any items
    that are displaced by an add, move or remove operation, without having to specify the
    individual addDisplaced, moveDisplaced and removeDisplaced properties. For example, here
    is a view that specifies a displaced transition:
 
    \code
    ListView {
        ...
        displaced: Transition {
            NumberAnimation { properties: "x,y"; duration: 1000 }
        }
    }
    \endcode
 
    When any item is added, moved or removed within the above view, the items below it are
    displaced, causing them to move down (or sideways, if horizontally orientated) within the
    view. As this displacement occurs, the items' movement to their new x,y positions within
    the view will be animated by a NumberAnimation over one second, as specified.
 
    If a view specifies this generic displaced transition as well as a specific addDisplaced,
    moveDisplaced or removeDisplaced transition, the more specific transition will be used
    instead of the generic displaced transition when the relevant operation occurs, providing that
    the more specific transition has not been disabled (by setting \l {Transition::enabled}{enabled}
    to false). If it has indeed been disabled, the generic displaced transition is applied instead.
 
    For more details and examples on how to use view transitions, see the ViewTransition
    documentation.
 
    \sa addDisplaced, moveDisplaced, removeDisplaced, ViewTransition
*/
 
void QQuickListView::viewportMoved(Qt::Orientations orient)
{
    Q_D(QQuickListView);
    QQuickItemView::viewportMoved(orient);
 
    if (!d->itemCount) {
        if (d->hasStickyHeader())
            d->updateHeader();
        if (d->hasStickyFooter())
            d->updateFooter();
        return;
    }
 
    // Recursion can occur due to refill changing the content size.
    if (d->inViewportMoved)
        return;
    d->inViewportMoved = true;
 
    if (yflick()) {
        if (d->isBottomToTop())
            d->bufferMode = d->vData.smoothVelocity < 0 ? QQuickListViewPrivate::BufferAfter : QQuickListViewPrivate::BufferBefore;
        else
            d->bufferMode = d->vData.smoothVelocity < 0 ? QQuickListViewPrivate::BufferBefore : QQuickListViewPrivate::BufferAfter;
    } else {
        if (d->isRightToLeft())
            d->bufferMode = d->hData.smoothVelocity < 0 ? QQuickListViewPrivate::BufferAfter : QQuickListViewPrivate::BufferBefore;
        else
            d->bufferMode = d->hData.smoothVelocity < 0 ? QQuickListViewPrivate::BufferBefore : QQuickListViewPrivate::BufferAfter;
    }
 
    d->refillOrLayout();
 
    // Set visibility of items to eliminate cost of items outside the visible area.
    qreal from = d->isContentFlowReversed() ? -d->position()-d->displayMarginBeginning-d->size() : d->position()-d->displayMarginBeginning;
    qreal to = d->isContentFlowReversed() ? -d->position()+d->displayMarginEnd : d->position()+d->size()+d->displayMarginEnd;
    for (FxViewItem *item : std::as_const(d->visibleItems)) {
        if (item->item)
            QQuickItemPrivate::get(item->item)->setCulled(item->endPosition() < from || item->position() > to);
    }
    if (d->currentItem)
        QQuickItemPrivate::get(d->currentItem->item)->setCulled(d->currentItem->endPosition() < from || d->currentItem->position() > to);
 
    if (d->hData.flicking || d->vData.flicking || d->hData.moving || d->vData.moving)
        d->moveReason = QQuickListViewPrivate::Mouse;
    if (d->moveReason != QQuickListViewPrivate::SetIndex) {
        if (d->haveHighlightRange && d->highlightRange == StrictlyEnforceRange && d->highlight) {
            // reposition highlight
            qreal pos = d->highlight->position();
            qreal viewPos = d->isContentFlowReversed() ? -d->position()-d->size() : d->position();
            if (pos > viewPos + d->highlightRangeEnd - d->highlight->size())
                pos = viewPos + d->highlightRangeEnd - d->highlight->size();
            if (pos < viewPos + d->highlightRangeStart)
                pos = viewPos + d->highlightRangeStart;
            if (pos != d->highlight->position()) {
                d->highlightPosAnimator->stop();
                static_cast<FxListItemSG*>(d->highlight.get())->setPosition(pos);
            } else {
                d->updateHighlight();
            }
 
            // update current index
            if (FxViewItem *snapItem = d->snapItemAt(d->highlight->position())) {
                if (snapItem->index >= 0 && snapItem->index != d->currentIndex)
                    d->updateCurrent(snapItem->index);
            }
        }
    }
 
    if ((d->hData.flicking || d->vData.flicking) && d->correctFlick && !d->inFlickCorrection) {
        d->inFlickCorrection = true;
        // Near an end and it seems that the extent has changed?
        // Recalculate the flick so that we don't end up in an odd position.
        if (yflick() && !d->vData.inOvershoot) {
            if (d->vData.velocity > 0) {
                const qreal minY = minYExtent();
                if ((minY - d->vData.move.value() < height()/2 || d->vData.flickTarget - d->vData.move.value() < height()/2)
                    && minY != d->vData.flickTarget)
                    d->flickY(QEvent::TouchUpdate, -d->vData.smoothVelocity.value());
            } else if (d->vData.velocity < 0) {
                const qreal maxY = maxYExtent();
                if ((d->vData.move.value() - maxY < height()/2 || d->vData.move.value() - d->vData.flickTarget < height()/2)
                    && maxY != d->vData.flickTarget)
                    d->flickY(QEvent::TouchUpdate, -d->vData.smoothVelocity.value());
            }
        }
 
        if (xflick() && !d->hData.inOvershoot) {
            if (d->hData.velocity > 0) {
                const qreal minX = minXExtent();
                if ((minX - d->hData.move.value() < width()/2 || d->hData.flickTarget - d->hData.move.value() < width()/2)
                    && minX != d->hData.flickTarget)
                    d->flickX(QEvent::TouchUpdate, -d->hData.smoothVelocity.value());
            } else if (d->hData.velocity < 0) {
                const qreal maxX = maxXExtent();
                if ((d->hData.move.value() - maxX < width()/2 || d->hData.move.value() - d->hData.flickTarget < width()/2)
                    && maxX != d->hData.flickTarget)
                    d->flickX(QEvent::TouchUpdate, -d->hData.smoothVelocity.value());
            }
        }
        d->inFlickCorrection = false;
    }
    if (d->hasStickyHeader())
        d->updateHeader();
    if (d->hasStickyFooter())
        d->updateFooter();
    if (d->sectionCriteria) {
        d->updateCurrentSection();
        d->updateStickySections();
    }
    d->inViewportMoved = false;
}
 
void QQuickListView::keyPressEvent(QKeyEvent *event)
{
    Q_D(QQuickListView);
    if (d->model && d->model->count() && ((d->interactive && !d->explicitKeyNavigationEnabled)
        || (d->explicitKeyNavigationEnabled && d->keyNavigationEnabled))) {
        if ((d->orient == QQuickListView::Horizontal && !d->isRightToLeft() && event->key() == Qt::Key_Left)
                    || (d->orient == QQuickListView::Horizontal && d->isRightToLeft() && event->key() == Qt::Key_Right)
                    || (d->orient == QQuickListView::Vertical && !d->isBottomToTop() && event->key() == Qt::Key_Up)
                    || (d->orient == QQuickListView::Vertical && d->isBottomToTop() && event->key() == Qt::Key_Down)) {
            if (currentIndex() > 0 || (d->wrap && !event->isAutoRepeat())) {
                decrementCurrentIndex();
                event->accept();
                return;
            } else if (d->wrap) {
                event->accept();
                return;
            }
        } else if ((d->orient == QQuickListView::Horizontal && !d->isRightToLeft() && event->key() == Qt::Key_Right)
                    || (d->orient == QQuickListView::Horizontal && d->isRightToLeft() && event->key() == Qt::Key_Left)
                   || (d->orient == QQuickListView::Vertical && !d->isBottomToTop() && event->key() == Qt::Key_Down)
                   || (d->orient == QQuickListView::Vertical && d->isBottomToTop() && event->key() == Qt::Key_Up)) {
            if (currentIndex() < d->model->count() - 1 || (d->wrap && !event->isAutoRepeat())) {
                incrementCurrentIndex();
                event->accept();
                return;
            } else if (d->wrap) {
                event->accept();
                return;
            }
        }
    }
    event->ignore();
    QQuickItemView::keyPressEvent(event);
}
 
void QQuickListView::geometryChange(const QRectF &newGeometry, const QRectF &oldGeometry)
{
    Q_D(QQuickListView);
 
    if (d->model) {
        // When the view changes size, we force the pool to
        // shrink by releasing all pooled items.
        d->model->drainReusableItemsPool(0);
    }
 
    if (d->isRightToLeft()) {
        // maintain position relative to the right edge
        qreal dx = newGeometry.width() - oldGeometry.width();
        setContentX(contentX() - dx);
    } else if (d->isBottomToTop()) {
        // maintain position relative to the bottom edge
        qreal dy = newGeometry.height() - oldGeometry.height();
        setContentY(contentY() - dy);
    }
 
    // When view-relative delegates resize, the content position becomes
    // stale and fixup() snaps to the wrong item. Record the current snap
    // target here; fixup() will use it instead of snapItemAt().
    // StrictlyEnforceRange is excluded — its fixup() path already forces
    // currentItem as the snap target.
    const bool vertical = (d->orient == QQuickListView::Vertical);
    const qreal oldSize = vertical ? oldGeometry.height() : oldGeometry.width();
    const qreal newSize = vertical ? newGeometry.height() : newGeometry.width();
 
    if (d->snapMode == QQuickListView::SnapOneItem
        && !(d->haveHighlightRange && d->highlightRange == QQuickListView::StrictlyEnforceRange)
        && !d->visibleItems.isEmpty() && !qFuzzyCompare(oldSize, newSize) && oldSize > 0) {
        qreal viewPos = d->isContentFlowReversed() ? -d->position() - d->size() : d->position();
        if (FxViewItem *snapped = d->snapItemAt(viewPos)) {
            if (snapped->index >= 0)
                d->snapResizeTargetIndex = snapped->index;
        }
    }
 
    QQuickItemView::geometryChange(newGeometry, oldGeometry);
}
 
void QQuickListView::initItem(int index, QObject *object)
{
    QQuickItemView::initItem(index, object);
 
    // setting the view from the FxViewItem wrapper is too late if the delegate
    // needs access to the view in Component.onCompleted
    QQuickItem *item = qmlobject_cast<QQuickItem*>(object);
    if (item) {
        QQuickListViewAttached *attached = static_cast<QQuickListViewAttached *>(
                qmlAttachedPropertiesObject<QQuickListView>(item));
        if (attached)
            attached->setView(this);
    }
}
 
qreal QQuickListView::maxYExtent() const
{
    Q_D(const QQuickListView);
    if (d->layoutOrientation() == Qt::Horizontal && d->flickableDirection != HorizontalFlick)
        return QQuickFlickable::maxYExtent();
    return QQuickItemView::maxYExtent();
}
 
qreal QQuickListView::maxXExtent() const
{
    Q_D(const QQuickListView);
    if (d->layoutOrientation() == Qt::Vertical && d->flickableDirection != VerticalFlick)
        return QQuickFlickable::maxXExtent();
    return QQuickItemView::maxXExtent();
}
 
/*!
    \qmlmethod void QtQuick::ListView::incrementCurrentIndex()
 
    Increments the current index.  The current index will wrap
    if keyNavigationWraps is true and it is currently at the end.
    This method has no effect if the \l count is zero.
 
    \b Note: methods should only be called after the Component has completed.
*/
void QQuickListView::incrementCurrentIndex()
{
    Q_D(QQuickListView);
    int count = d->model ? d->model->count() : 0;
    if (count && (currentIndex() < count - 1 || d->wrap)) {
        d->moveReason = QQuickListViewPrivate::SetIndex;
        int index = currentIndex()+1;
        setCurrentIndex((index >= 0 && index < count) ? index : 0);
    }
}
 
/*!
    \qmlmethod void QtQuick::ListView::decrementCurrentIndex()
 
    Decrements the current index.  The current index will wrap
    if keyNavigationWraps is true and it is currently at the beginning.
    This method has no effect if the \l count is zero.
 
    \b Note: methods should only be called after the Component has completed.
*/
void QQuickListView::decrementCurrentIndex()
{
    Q_D(QQuickListView);
    int count = d->model ? d->model->count() : 0;
    if (count && (currentIndex() > 0 || d->wrap)) {
        d->moveReason = QQuickListViewPrivate::SetIndex;
        int index = currentIndex()-1;
        setCurrentIndex((index >= 0 && index < count) ? index : count-1);
    }
}
 
void QQuickListViewPrivate::updateSectionCriteria()
{
    Q_Q(QQuickListView);
    if (q->isComponentComplete() && model) {
        QList<QByteArray> roles;
        if (sectionCriteria && !sectionCriteria->property().isEmpty())
            roles << sectionCriteria->property().toUtf8();
        model->setWatchedRoles(roles);
        updateSections();
        if (itemCount)
            forceLayoutPolish();
    }
}
 
bool QQuickListViewPrivate::applyInsertionChange(const QQmlChangeSet::Change &change, ChangeResult *insertResult, QList<FxViewItem *> *addedItems, QList<MovedItem> *movingIntoView)
{
    Q_Q(QQuickListView);
#if !QT_CONFIG(quick_viewtransitions)
    Q_UNUSED(movingIntoView)
#endif
    int modelIndex = change.index;
    int count = change.count;
 
    if (q->size().isNull() && visibleItems.isEmpty())
        return false;
 
    qreal tempPos = isContentFlowReversed() ? -position()-size() : position();
    int index = visibleItems.size() ? mapFromModel(modelIndex) : 0;
    qreal lastVisiblePos = buffer + displayMarginEnd + tempPos + size();
 
    if (index < 0) {
        int i = visibleItems.size() - 1;
        while (i > 0 && visibleItems.at(i)->index == -1)
            --i;
        if (i == 0 && visibleItems.constFirst()->index == -1) {
            // there are no visible items except items marked for removal
            index = visibleItems.size();
        } else if (visibleItems.at(i)->index + 1 == modelIndex
            && visibleItems.at(i)->endPosition() <= lastVisiblePos) {
            // Special case of appending an item to the model.
            index = visibleItems.size();
        } else {
            if (modelIndex < visibleIndex) {
                // Insert before visible items
                visibleIndex += count;
                for (FxViewItem *item : std::as_const(visibleItems)) {
                    if (item->index != -1 && item->index >= modelIndex)
                        item->index += count;
                }
            }
            return true;
        }
    }
 
    // index can be the next item past the end of the visible items list (i.e. appended)
    qreal pos = 0;
    if (visibleItems.size()) {
        pos = index < visibleItems.size() ? visibleItems.at(index)->position()
                                                : visibleItems.constLast()->endPosition() + spacing;
    }
 
    // Update the indexes of the following visible items.
    for (FxViewItem *item : std::as_const(visibleItems)) {
        if (item->index != -1 && item->index >= modelIndex) {
            item->index += count;
#if QT_CONFIG(quick_viewtransitions)
            if (change.isMove())
                item->transitionNextReposition(transitioner, QQuickItemViewTransitioner::MoveTransition, false);
            else
                item->transitionNextReposition(transitioner, QQuickItemViewTransitioner::AddTransition, false);
#endif
        }
    }
 
    bool visibleAffected = false;
    if (insertResult->visiblePos.isValid() && pos < insertResult->visiblePos) {
        // Insert items before the visible item.
        int insertionIdx = index;
        qreal from = tempPos - displayMarginBeginning - buffer;
 
        if (insertionIdx < visibleIndex) {
            if (pos >= from) {
                // items won't be visible, just note the size for repositioning
                insertResult->sizeChangesBeforeVisiblePos += count * (averageSize + spacing);
            }
        } else {
            MutableModelIterator it(model, modelIndex + count - 1, modelIndex -1);
            for (; it.hasNext() && pos >= from; it.next()) {
                // item is before first visible e.g. in cache buffer
                FxViewItem *item = nullptr;
                if (change.isMove() && (item = currentChanges.removedItems.take(change.moveKey(it.index))))
                    item->index = it.index;
                if (!item)
                    item = createItem(it.index, QQmlIncubator::Synchronous);
                if (!item)
                    return false;
                if (it.removedAtIndex)
                    continue;
 
                visibleAffected = true;
                visibleItems.insert(insertionIdx, item);
                if (insertionIdx == 0)
                    insertResult->changedFirstItem = true;
                if (!change.isMove()) {
                    addedItems->append(item);
#if QT_CONFIG(quick_viewtransitions)
                    if (transitioner)
                        item->transitionNextReposition(transitioner, QQuickItemViewTransitioner::AddTransition, true);
                    else
#endif
                        static_cast<FxListItemSG *>(item)->setPosition(pos, true);
                }
                insertResult->sizeChangesBeforeVisiblePos += item->size() + spacing;
                pos -= item->size() + spacing;
                index++;
            }
        }
 
        int firstOkIdx = -1;
        for (int i = 0; i <= insertionIdx && i < visibleItems.size() - 1; i++) {
            if (visibleItems.at(i)->index + 1 != visibleItems.at(i + 1)->index) {
                firstOkIdx = i + 1;
                break;
            }
        }
        for (int i = 0; i < firstOkIdx; i++) {
            FxViewItem *nvItem = visibleItems.takeFirst();
            addedItems->removeOne(nvItem);
            removeItem(nvItem);
        }
 
    } else {
        MutableModelIterator it(model, modelIndex, modelIndex + count);
        for (; it.hasNext() && pos <= lastVisiblePos; it.next()) {
            visibleAffected = true;
            FxViewItem *item = nullptr;
            if (change.isMove() && (item = currentChanges.removedItems.take(change.moveKey(it.index))))
                item->index = it.index;
#if QT_CONFIG(quick_viewtransitions)
            bool newItem = !item;
#endif
            it.removedAtIndex = false;
            if (!item)
                item = createItem(it.index, QQmlIncubator::Synchronous);
            if (!item)
                return false;
            if (it.removedAtIndex) {
                releaseItem(item, reusableFlag);
                continue;
            }
 
            if (index < visibleItems.size())
                visibleItems.insert(index, item);
            else // special case of appending an item to the model - as above
                visibleItems.append(item);
            if (index == 0)
                insertResult->changedFirstItem = true;
            if (change.isMove()) {
                // we know this is a move target, since move displaced items that are
                // shuffled into view due to a move would be added in refill()
#if QT_CONFIG(quick_viewtransitions)
                if (newItem && transitioner && transitioner->canTransition(QQuickItemViewTransitioner::MoveTransition, true))
                    movingIntoView->append(MovedItem(item, change.moveKey(item->index)));
#endif
            } else {
                addedItems->append(item);
#if QT_CONFIG(quick_viewtransitions)
                if (transitioner)
                    item->transitionNextReposition(transitioner, QQuickItemViewTransitioner::AddTransition, true);
                else
#endif
                    static_cast<FxListItemSG *>(item)->setPosition(pos, true);
            }
            insertResult->sizeChangesAfterVisiblePos += item->size() + spacing;
            pos += item->size() + spacing;
            ++index;
        }
        it.disconnect();
 
        if (0 < index && index < visibleItems.size()) {
            FxViewItem *prevItem = visibleItems.at(index - 1);
            FxViewItem *item = visibleItems.at(index);
            if (prevItem->index != item->index - 1) {
                int i = index;
#if QT_CONFIG(quick_viewtransitions)
                qreal prevPos = prevItem->position();
#endif
                while (i < visibleItems.size()) {
                    FxListItemSG *nvItem = static_cast<FxListItemSG *>(visibleItems.takeLast());
                    insertResult->sizeChangesAfterVisiblePos -= nvItem->size() + spacing;
                    addedItems->removeOne(nvItem);
#if QT_CONFIG(quick_viewtransitions)
                    if (nvItem->transitionScheduledOrRunning())
                        nvItem->setPosition(prevPos + (nvItem->index - prevItem->index) * averageSize);
#endif
                    removeItem(nvItem);
                }
            }
        }
    }
 
    updateVisibleIndex();
 
    return visibleAffected;
}
 
#if QT_CONFIG(quick_viewtransitions)
void QQuickListViewPrivate::translateAndTransitionItemsAfter(int afterModelIndex, const ChangeResult &insertionResult, const ChangeResult &removalResult)
{
    Q_UNUSED(insertionResult);
 
    if (!transitioner)
        return;
 
    int markerItemIndex = -1;
    for (int i=0; i<visibleItems.size(); i++) {
        if (visibleItems.at(i)->index == afterModelIndex) {
            markerItemIndex = i;
            break;
        }
    }
    if (markerItemIndex < 0)
        return;
 
    const qreal viewEndPos = isContentFlowReversed() ? -position() : position() + size();
    qreal sizeRemoved = -removalResult.sizeChangesAfterVisiblePos
            - (removalResult.countChangeAfterVisibleItems * (averageSize + spacing));
 
    for (int i=markerItemIndex+1; i<visibleItems.size(); i++) {
        FxListItemSG *listItem = static_cast<FxListItemSG *>(visibleItems.at(i));
        if (listItem->position() >= viewEndPos)
            break;
        if (!listItem->transitionScheduledOrRunning()) {
            qreal pos = listItem->position();
            listItem->setPosition(pos - sizeRemoved);
            listItem->transitionNextReposition(transitioner, QQuickItemViewTransitioner::RemoveTransition, false);
            listItem->setPosition(pos);
        }
    }
}
#endif
 
/*!
    \qmlmethod void QtQuick::ListView::positionViewAtIndex(int index, PositionMode mode)
 
    Positions the view such that the \a index is at the position specified by \a mode:
 
    \value ListView.Beginning   position item at the top (or left for horizontal orientation) of the view.
    \value ListView.Center      position item in the center of the view.
    \value ListView.End         position item at bottom (or right for horizontal orientation) of the view.
    \value ListView.Visible     if any part of the item is visible then take no action, otherwise
                                bring the item into view.
    \value ListView.Contain     ensure the entire item is visible. If the item is larger than the view,
                                the item is positioned at the top (or left for horizontal orientation) of the view.
    \value ListView.SnapPosition position the item at \l preferredHighlightBegin.  This mode is only valid
                                if \l highlightRangeMode is StrictlyEnforceRange or snapping is enabled via \l snapMode.
 
    If positioning the view at \a index would cause empty space to be displayed at
    the beginning or end of the view, the view will be positioned at the boundary.
 
    It is not recommended to use \l {Flickable::}{contentX} or \l {Flickable::}{contentY} to position the view
    at a particular index.  This is unreliable since removing items from the start
    of the list does not cause all other items to be repositioned, and because
    the actual start of the view can vary based on the size of the delegates.
    The correct way to bring an item into view is with \c positionViewAtIndex.
 
    \b Note: methods should only be called after the Component has completed.  To position
    the view at startup, this method should be called by Component.onCompleted.  For
    example, to position the view at the end:
 
    \code
    Component.onCompleted: positionViewAtIndex(count - 1, ListView.Beginning)
    \endcode
*/
 
/*!
    \qmlmethod void QtQuick::ListView::positionViewAtBeginning()
    \qmlmethod void QtQuick::ListView::positionViewAtEnd()
 
    Positions the view at the beginning or end, taking into account any header or footer.
 
    It is not recommended to use \l {Flickable::}{contentX} or \l {Flickable::}{contentY} to position the view
    at a particular index.  This is unreliable since removing items from the start
    of the list does not cause all other items to be repositioned, and because
    the actual start of the view can vary based on the size of the delegates.
 
    \b Note: methods should only be called after the Component has completed.  To position
    the view at startup, this method should be called by Component.onCompleted.  For
    example, to position the view at the end on startup:
 
    \code
    Component.onCompleted: positionViewAtEnd()
    \endcode
*/
 
/*!
    \qmlmethod int QtQuick::ListView::indexAt(real x, real y)
 
    Returns the index of the visible item containing the point \a x, \a y in content
    coordinates.  If there is no item at the point specified, or the item is
    not visible -1 is returned.
 
    If the item is outside the visible area, -1 is returned, regardless of
    whether an item will exist at that point when scrolled into view.
 
    \b Note: methods should only be called after the Component has completed.
*/
 
/*!
    \qmlmethod Item QtQuick::ListView::itemAt(real x, real y)
 
    Returns the visible item containing the point \a x, \a y in content
    coordinates.  If there is no item at the point specified, or the item is
    not visible null is returned.
 
    If the item is outside the visible area, null is returned, regardless of
    whether an item will exist at that point when scrolled into view.
 
    \b Note: methods should only be called after the Component has completed.
*/
 
/*!
    \qmlmethod Item QtQuick::ListView::itemAtIndex(int index)
 
    Returns the item for \a index. If there is no item for that index, for example
    because it has not been created yet, or because it has been panned out of
    the visible area and removed from the cache, null is returned.
 
    \b Note: this method should only be called after the Component has completed.
    The returned value should also not be stored since it can turn to null
    as soon as control goes out of the calling scope, if the view releases that item.
 
    \since 5.13
*/
 
/*!
    \qmlmethod void QtQuick::ListView::forceLayout()
 
    Responding to changes in the model is usually batched to happen only once
    per frame. This means that inside script blocks it is possible for the
    underlying model to have changed, but the ListView has not caught up yet.
 
    This method forces the ListView to immediately respond to any outstanding
    changes in the model.
 
    \since 5.1
 
    \b Note: methods should only be called after the Component has completed.
*/
 
QQuickListViewAttached *QQuickListView::qmlAttachedProperties(QObject *obj)
{
    return new QQuickListViewAttached(obj);
}
 
/*! \internal
    Prevents clicking or dragging through floating headers (QTBUG-74046).
*/
bool QQuickListViewPrivate::wantsPointerEvent(const QPointerEvent *event)
{
    Q_Q(const QQuickListView);
    bool ret = true;
 
    QPointF pos = event->points().first().position();
    if (!pos.isNull()) {
        if (auto header = q->headerItem()) {
            if (q->headerPositioning() != QQuickListView::InlineHeader &&
                    header->contains(q->mapToItem(header, pos)))
                ret = false;
        }
        if (auto footer = q->footerItem()) {
            if (q->footerPositioning() != QQuickListView::InlineFooter &&
                    footer->contains(q->mapToItem(footer, pos)))
                ret = false;
        }
    }
 
    switch (event->type()) {
    case QEvent::MouseButtonPress:
        wantedMousePress = ret;
        break;
    case QEvent::MouseMove:
        ret = wantedMousePress;
        break;
    default:
        break;
    }
 
    qCDebug(lcEvents) << q << (ret ? "WANTS" : "DOESN'T want") << event;
    return ret;
}
 
QT_END_NAMESPACE
 
#include "moc_qquicklistview_p.cpp"