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dragwidget.cpp Example File
draganddrop/draggableicons/dragwidget.cpp

 /****************************************************************************
 **
 ** Copyright (C) 2005-2008 Trolltech ASA. All rights reserved.
 **
 ** This file is part of the example classes of the Qt Toolkit.
 **
 ** Licensees holding a valid Qt License Agreement may use this file in
 ** accordance with the rights, responsibilities and obligations
 ** contained therein.  Please consult your licensing agreement or
 ** contact sales@trolltech.com if any conditions of this licensing
 ** agreement are not clear to you.
 **
 ** Further information about Qt licensing is available at:
 ** http://www.trolltech.com/products/qt/licensing.html or by
 ** contacting info@trolltech.com.
 **
 ** This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
 ** WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 **
 ****************************************************************************/

 #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::dragMoveEvent(QDragMoveEvent *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->exec(Qt::CopyAction | Qt::MoveAction, Qt::CopyAction) == Qt::MoveAction)
         child->close();
     else {
         child->show();
         child->setPixmap(pixmap);
     }
 }


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Qt 4.3.5