myscrollarea.cpp

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// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
 
#include <QtWidgets>
 
class MyScrollArea : public QAbstractScrollArea
{
public:
    MyScrollArea(QWidget *w);
    void setWidget(QWidget *w);
 
protected:
    void scrollContentsBy(int dx, int dy) override;
    void resizeEvent(QResizeEvent *event) override;
 
private:
    void updateWidgetPosition();
    void updateArea();
 
    QWidget *widget;
};
 
MyScrollArea::MyScrollArea(QWidget *widget)
    : QAbstractScrollArea()
{
    setWidget(widget);
}
 
void MyScrollArea::setWidget(QWidget *w)
{
    widget = w;
    widget->setParent(viewport());
    if (!widget->testAttribute(Qt::WA_Resized))
        widget->resize(widget->sizeHint());
 
    verticalScrollBar()->setValue(0);
    verticalScrollBar()->setValue(0);
 
    updateArea();
}
 
void MyScrollArea::updateWidgetPosition()
{
    //! [0]
    int hvalue = horizontalScrollBar()->value();
    int vvalue = verticalScrollBar()->value();
    QPoint topLeft = viewport()->rect().topLeft();
 
    widget->move(topLeft.x() - hvalue, topLeft.y() - vvalue);
    //! [0]
}
 
void MyScrollArea::scrollContentsBy(int dx, int dy)
{
    Q_UNUSED(dx);
    Q_UNUSED(dy);
    updateWidgetPosition();
}
 
void MyScrollArea::updateArea()
{
    //! [1]
    QSize areaSize = viewport()->size();
    QSize  widgetSize = widget->size();
 
    verticalScrollBar()->setPageStep(areaSize.height());
    horizontalScrollBar()->setPageStep(areaSize.width());
    verticalScrollBar()->setRange(0, widgetSize.height() - areaSize.height());
    horizontalScrollBar()->setRange(0, widgetSize.width() - areaSize.width());
    updateWidgetPosition();
    //! [1]
}
 
void MyScrollArea::resizeEvent(QResizeEvent *event)
{
    Q_UNUSED(event);
    updateArea();
}