qdrag.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
 
#include <qdrag.h>
#include "private/qguiapplication_p.h"
#include "qpa/qplatformintegration.h"
#include "qpa/qplatformdrag.h"
#include <qpixmap.h>
#include <qpoint.h>
#include "qdnd_p.h"
 
#include <QtCore/qpointer.h>
 
QT_BEGIN_NAMESPACE
 
/*!
    \class QDrag
    \inmodule QtGui
    \ingroup draganddrop
    \brief The QDrag class provides support for MIME-based drag and drop data
    transfer.
 
    Drag and drop is an intuitive way for users to copy or move data around in an
    application, and is used in many desktop environments as a mechanism for copying
    data between applications. Drag and drop support in Qt is centered around the
    QDrag class that handles most of the details of a drag and drop operation.
 
    The data to be transferred by the drag and drop operation is contained in a
    QMimeData object. This is specified with the setMimeData() function in the
    following way:
 
    \snippet dragging/mainwindow.cpp 1
 
    Note that setMimeData() assigns ownership of the QMimeData object to the
    QDrag object. The QDrag must be constructed on the heap with a parent QObject
    to ensure that Qt can clean up after the drag and drop operation has been
    completed.
 
    A pixmap can be used to represent the data while the drag is in
    progress, and will move with the cursor to the drop target. This
    pixmap typically shows an icon that represents the MIME type of
    the data being transferred, but any pixmap can be set with
    setPixmap(). The cursor's hot spot can be given a position
    relative to the top-left corner of the pixmap with the
    setHotSpot() function. The following code positions the pixmap so
    that the cursor's hot spot points to the center of its bottom
    edge:
 
    \snippet separations/finalwidget.cpp 2
 
    \note On X11, the pixmap may not be able to keep up with the mouse
    movements if the hot spot causes the pixmap to be displayed
    directly under the cursor.
 
    The source and target widgets can be found with source() and target().
    These functions are often used to determine whether drag and drop operations
    started and finished at the same widget, so that special behavior can be
    implemented.
 
    QDrag only deals with the drag and drop operation itself. It is up to the
    developer to decide when a drag operation begins, and how a QDrag object should
    be constructed and used. For a given widget, it is often necessary to
    reimplement \l{QWidget::mousePressEvent()}{mousePressEvent()} to determine
    whether the user has pressed a mouse button, and reimplement
    \l{QWidget::mouseMoveEvent()}{mouseMoveEvent()} to check whether a QDrag is
    required.
 
    \sa {Drag and Drop}, QClipboard, QMimeData, {Draggable Icons Example},
        {Draggable Text Example}, {Drop Site Example}
*/
 
/*!
    Constructs a new drag object for the widget specified by \a dragSource.
*/
QDrag::QDrag(QObject *dragSource)
    : QObject(*new QDragPrivate, dragSource)
{
    Q_D(QDrag);
    d->source = dragSource;
    d->target = nullptr;
    d->data = nullptr;
    d->hotspot = QPoint(-10, -10);
    d->executed_action = Qt::IgnoreAction;
    d->supported_actions = Qt::IgnoreAction;
    d->default_action = Qt::IgnoreAction;
}
 
/*!
    Destroys the drag object.
*/
QDrag::~QDrag()
{
    Q_D(QDrag);
    delete d->data;
}
 
/*!
    Sets the data to be sent to the given MIME \a data. Ownership of the data is
    transferred to the QDrag object.
*/
void QDrag::setMimeData(QMimeData *data)
{
    Q_D(QDrag);
    if (d->data == data)
        return;
    if (d->data != nullptr)
        delete d->data;
    d->data = data;
}
 
/*!
    Returns the MIME data that is encapsulated by the drag object.
*/
QMimeData *QDrag::mimeData() const
{
    Q_D(const QDrag);
    return d->data;
}
 
/*!
    Sets \a pixmap as the pixmap used to represent the data in a drag
    and drop operation. You can only set a pixmap before the drag is
    started.
*/
void QDrag::setPixmap(const QPixmap &pixmap)
{
    Q_D(QDrag);
    d->pixmap = pixmap;
}
 
/*!
    Returns the pixmap used to represent the data in a drag and drop operation.
*/
QPixmap QDrag::pixmap() const
{
    Q_D(const QDrag);
    return d->pixmap;
}
 
/*!
    Sets the position of the hot spot relative to the top-left corner of the
    pixmap used to the point specified by \a hotspot.
 
    \b{Note:} on X11, the pixmap may not be able to keep up with the mouse
    movements if the hot spot causes the pixmap to be displayed
    directly under the cursor.
*/
void QDrag::setHotSpot(const QPoint& hotspot)
{
    Q_D(QDrag);
    d->hotspot = hotspot;
}
 
/*!
    Returns the position of the hot spot relative to the top-left corner of the
    cursor.
*/
QPoint QDrag::hotSpot() const
{
    Q_D(const QDrag);
    return d->hotspot;
}
 
/*!
    Returns the source of the drag object. This is the widget where the drag
    and drop operation originated.
*/
QObject *QDrag::source() const
{
    Q_D(const QDrag);
    return d->source;
}
 
/*!
    Returns the target of the drag and drop operation. This is the widget where
    the drag object was dropped.
*/
QObject *QDrag::target() const
{
    Q_D(const QDrag);
    return d->target;
}
 
/*!
    \since 4.3
 
    Starts the drag and drop operation and returns a value indicating the requested
    drop action when it is completed. The drop actions that the user can choose
    from are specified in \a supportedActions. The default proposed action will be selected
    among the allowed actions in the following order: Move, Copy and Link.
 
    \b{Note:} On Linux and \macos, the drag and drop operation
    can take some time, but this function does not block the event
    loop. Other events are still delivered to the application while
    the operation is performed. On Windows, the Qt event loop is
    blocked during the operation.
 
    \sa cancel()
*/
 
Qt::DropAction QDrag::exec(Qt::DropActions supportedActions)
{
    return exec(supportedActions, Qt::IgnoreAction);
}
 
/*!
    \since 4.3
 
    Starts the drag and drop operation and returns a value indicating the requested
    drop action when it is completed. The drop actions that the user can choose
    from are specified in \a supportedActions.
 
    The \a defaultDropAction determines which action will be proposed when the user performs a
    drag without using modifier keys.
 
    \b{Note:} On Linux and \macos, the drag and drop operation
    can take some time, but this function does not block the event
    loop. Other events are still delivered to the application while
    the operation is performed. On Windows, the Qt event loop is
    blocked during the operation. However, QDrag::exec() on
    Windows causes processEvents() to be called frequently to keep the GUI responsive.
    If any loops or operations are called while a drag operation is active, it will block the drag operation.
*/
 
Qt::DropAction QDrag::exec(Qt::DropActions supportedActions, Qt::DropAction defaultDropAction)
{
    Q_D(QDrag);
    if (!d->data) {
        qWarning("QDrag: No mimedata set before starting the drag");
        return d->executed_action;
    }
    Qt::DropAction transformedDefaultDropAction = Qt::IgnoreAction;
 
    if (defaultDropAction == Qt::IgnoreAction) {
        if (supportedActions & Qt::MoveAction) {
            transformedDefaultDropAction = Qt::MoveAction;
        } else if (supportedActions & Qt::CopyAction) {
            transformedDefaultDropAction = Qt::CopyAction;
        } else if (supportedActions & Qt::LinkAction) {
            transformedDefaultDropAction = Qt::LinkAction;
        }
    } else {
        transformedDefaultDropAction = defaultDropAction;
    }
    d->supported_actions = supportedActions;
    d->default_action = transformedDefaultDropAction;
    QPointer<QDrag> self = this;
    auto executed_action = QDragManager::self()->drag(self.data());
    if (self.isNull())
        return Qt::IgnoreAction;
    d->executed_action = executed_action;
    return d->executed_action;
}
 
/*!
    Sets the drag \a cursor for the \a action. This allows you
    to override the default native cursors. To revert to using the
    native cursor for \a action pass in a null QPixmap as \a cursor.
 
    Note: setting the drag cursor for IgnoreAction may not work on
    all platforms. X11 and macOS has been tested to work. Windows
    does not support it.
*/
void QDrag::setDragCursor(const QPixmap &cursor, Qt::DropAction action)
{
    Q_D(QDrag);
    if (cursor.isNull())
        d->customCursors.remove(action);
    else
        d->customCursors[action] = cursor;
}
 
/*!
    Returns the drag cursor for the \a action.
 
    \since 5.0
*/
 
QPixmap QDrag::dragCursor(Qt::DropAction action) const
{
    typedef QMap<Qt::DropAction, QPixmap>::const_iterator Iterator;
 
    Q_D(const QDrag);
    const Iterator it = d->customCursors.constFind(action);
    if (it != d->customCursors.constEnd())
        return it.value();
 
    Qt::CursorShape shape = Qt::ForbiddenCursor;
    switch (action) {
    case Qt::MoveAction:
        shape = Qt::DragMoveCursor;
        break;
    case Qt::CopyAction:
        shape = Qt::DragCopyCursor;
        break;
    case Qt::LinkAction:
        shape = Qt::DragLinkCursor;
        break;
    default:
        shape = Qt::ForbiddenCursor;
    }
    return QGuiApplicationPrivate::instance()->getPixmapCursor(shape);
}
 
/*!
    Returns the set of possible drop actions for this drag operation.
 
    \sa exec(), defaultAction()
*/
Qt::DropActions QDrag::supportedActions() const
{
    Q_D(const QDrag);
    return d->supported_actions;
}
 
 
/*!
    Returns the default proposed drop action for this drag operation.
 
    \sa exec(), supportedActions()
*/
Qt::DropAction QDrag::defaultAction() const
{
    Q_D(const QDrag);
    return d->default_action;
}
 
/*!
    Cancels a drag operation initiated by Qt.
 
    \note This is currently implemented on Windows and X11.
 
    \since 5.7
    \sa exec()
*/
void QDrag::cancel()
{
    if (QPlatformDrag *platformDrag = QGuiApplicationPrivate::platformIntegration()->drag())
        platformDrag->cancelDrag();
}
 
/*!
    \fn void QDrag::actionChanged(Qt::DropAction action)
 
    This signal is emitted when the \a action associated with the
    drag changes.
 
    \sa targetChanged()
*/
 
/*!
    \fn void QDrag::targetChanged(QObject *newTarget)
 
    This signal is emitted when the target of the drag and drop
    operation changes, with \a newTarget the new target.
 
    \sa target(), actionChanged()
*/
 
QT_END_NAMESPACE
 
#include "moc_qdrag.cpp"