Qt 4.3: dragwidget.cpp Example File (draganddrop/draggableicons/dragwidget.cpp)

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

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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::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);
         }
     }