dragwidget.cpp Example File
^{draganddrop/draggableicons/dragwidget.cpp}

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    **
    ** Copyright (C) 2005-2006 Trolltech ASA. All rights reserved.
    **
    ** This file is part of the documentation of the Qt Toolkit.
    **
    ** This file may be used under the terms of the GNU General Public
    ** License version 2.0 as published by the Free Software Foundation
    ** and appearing in the file LICENSE.GPL included in the packaging of
    ** this file.  Please review the following information to ensure GNU
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    ** review the following information:
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    ** WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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    #include <QtGui>

    #include "dragwidget.h"

    DragWidget::DragWidget(QWidget *parent)
        : QFrame(parent)
    {
        setMinimumSize(200, 200);
        setFrameStyle(QFrame::Sunken | QFrame::StyledPanel);
        setAcceptDrops(true);

        QLabel *boatIcon = new QLabel(this);
        boatIcon->setPixmap(QPixmap(":/images/boat.png"));
        boatIcon->move(20, 20);
        boatIcon->show();
        boatIcon->setAttribute(Qt::WA_DeleteOnClose);

        QLabel *carIcon = new QLabel(this);
        carIcon->setPixmap(QPixmap(":/images/car.png"));
        carIcon->move(120, 20);
        carIcon->show();
        carIcon->setAttribute(Qt::WA_DeleteOnClose);

        QLabel *houseIcon = new QLabel(this);
        houseIcon->setPixmap(QPixmap(":/images/house.png"));
        houseIcon->move(20, 120);
        houseIcon->show();
        houseIcon->setAttribute(Qt::WA_DeleteOnClose);
    }

    void DragWidget::dragEnterEvent(QDragEnterEvent *event)
    {
        if (event->mimeData()->hasFormat("application/x-dnditemdata")) {
            if (event->source() == this) {
                event->setDropAction(Qt::MoveAction);
                event->accept();
            } else {
                event->acceptProposedAction();
            }
        } else {
            event->ignore();
        }
    }

    void DragWidget::dropEvent(QDropEvent *event)
    {
        if (event->mimeData()->hasFormat("application/x-dnditemdata")) {
            QByteArray itemData = event->mimeData()->data("application/x-dnditemdata");
            QDataStream dataStream(&itemData, QIODevice::ReadOnly);

            QPixmap pixmap;
            QPoint offset;
            dataStream >> pixmap >> offset;

            QLabel *newIcon = new QLabel(this);
            newIcon->setPixmap(pixmap);
            newIcon->move(event->pos() - offset);
            newIcon->show();
            newIcon->setAttribute(Qt::WA_DeleteOnClose);

            if (event->source() == this) {
                event->setDropAction(Qt::MoveAction);
                event->accept();
            } else {
                event->acceptProposedAction();
            }
        } else {
            event->ignore();
        }
    }

    void DragWidget::mousePressEvent(QMouseEvent *event)
    {
        QLabel *child = static_cast<QLabel*>(childAt(event->pos()));
        if (!child)
            return;

        QPixmap pixmap = *child->pixmap();

        QByteArray itemData;
        QDataStream dataStream(&itemData, QIODevice::WriteOnly);
        dataStream << pixmap << QPoint(event->pos() - child->pos());

        QMimeData *mimeData = new QMimeData;
        mimeData->setData("application/x-dnditemdata", itemData);

        QDrag *drag = new QDrag(this);
        drag->setMimeData(mimeData);
        drag->setPixmap(pixmap);
        drag->setHotSpot(event->pos() - child->pos());

        QPixmap tempPixmap = pixmap;
        QPainter painter;
        painter.begin(&tempPixmap);
        painter.fillRect(pixmap.rect(), QColor(127, 127, 127, 127));
        painter.end();

        child->setPixmap(tempPixmap);

        if (drag->start(Qt::CopyAction | Qt::MoveAction) == Qt::MoveAction)
            child->close();
        else {
            child->show();
            child->setPixmap(pixmap);
        }
    }