source: trunk/src/gui/kernel/qdrag.cpp@ 466

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#include <qwidget.h>
#include <qdrag.h>
#include <qpixmap.h>
#include <qpoint.h>
#include "qdnd_p.h"

#ifndef QT_NO_DRAGANDDROP

QT_BEGIN_NAMESPACE

/*!
    \class QDrag
    \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 doc/src/snippets/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 QWidget
    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 doc/src/snippets/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, QWindowsMime, QMacPasteboardMime,