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dragwidget.cpp Example File
draganddrop/fridgemagnets/dragwidget.cpp

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 ** This file is part of the examples of the Qt Toolkit.
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 ** GNU Lesser General Public License Usage
 ** Alternatively, this file may be used under the terms of the GNU Lesser
 ** General Public License version 2.1 as published by the Free Software
 ** Foundation and appearing in the file LICENSE.LGPL included in the
 ** packaging of this file.  Please review the following information to
 ** ensure the GNU Lesser General Public License version 2.1 requirements
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 ** Alternatively, this file may be used under the terms of the GNU
 ** General Public License version 3.0 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
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 #include <QtGui>

 #include "draglabel.h"
 #include "dragwidget.h"

 DragWidget::DragWidget(QWidget *parent)
     : QWidget(parent)
 {
     QFile dictionaryFile(":/dictionary/words.txt");
     dictionaryFile.open(QFile::ReadOnly);
     QTextStream inputStream(&dictionaryFile);

     int x = 5;
     int y = 5;

     while (!inputStream.atEnd()) {
         QString word;
         inputStream >> word;
         if (!word.isEmpty()) {
             DragLabel *wordLabel = new DragLabel(word, this);
             wordLabel->move(x, y);
             wordLabel->show();
             wordLabel->setAttribute(Qt::WA_DeleteOnClose);
             x += wordLabel->width() + 2;
             if (x >= 245) {
                 x = 5;
                 y += wordLabel->height() + 2;
             }
         }
     }

     #ifndef Q_WS_S60
     //Fridge magnets is used for demoing Qt on S60 and themed backgrounds look better than white
     QPalette newPalette = palette();
     newPalette.setColor(QPalette::Window, Qt::white);
     setPalette(newPalette);
     #endif

     setMinimumSize(400, qMax(200, y));
     setWindowTitle(tr("Fridge Magnets"));
     setAcceptDrops(true);
 }

 void DragWidget::dragEnterEvent(QDragEnterEvent *event)
 {
     if (event->mimeData()->hasFormat("application/x-fridgemagnet")) {
         if (children().contains(event->source())) {
             event->setDropAction(Qt::MoveAction);
             event->accept();
         } else {
             event->acceptProposedAction();
         }
     } else if (event->mimeData()->hasText()) {
         event->acceptProposedAction();
     } else {
         event->ignore();
     }
 }

 void DragWidget::dragMoveEvent(QDragMoveEvent *event)
 {
     if (event->mimeData()->hasFormat("application/x-fridgemagnet")) {
         if (children().contains(event->source())) {
             event->setDropAction(Qt::MoveAction);
             event->accept();
         } else {
             event->acceptProposedAction();
         }
     } else if (event->mimeData()->hasText()) {
         event->acceptProposedAction();
     } else {
         event->ignore();
     }
 }

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

         QString text;
         QPoint offset;
         dataStream >> text >> offset;
         DragLabel *newLabel = new DragLabel(text, this);
         newLabel->move(event->pos() - offset);
         newLabel->show();
         newLabel->setAttribute(Qt::WA_DeleteOnClose);

         if (event->source() == this) {
             event->setDropAction(Qt::MoveAction);
             event->accept();
         } else {
             event->acceptProposedAction();
         }
     } else if (event->mimeData()->hasText()) {
         QStringList pieces = event->mimeData()->text().split(QRegExp("\\s+"),
                              QString::SkipEmptyParts);
         QPoint position = event->pos();

         foreach (QString piece, pieces) {
             DragLabel *newLabel = new DragLabel(piece, this);
             newLabel->move(position);
             newLabel->show();
             newLabel->setAttribute(Qt::WA_DeleteOnClose);

             position += QPoint(newLabel->width(), 0);
         }

         event->acceptProposedAction();
     } else {
         event->ignore();
     }
 }

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

     QPoint hotSpot = event->pos() - child->pos();

     QByteArray itemData;
     QDataStream dataStream(&itemData, QIODevice::WriteOnly);
     dataStream << child->labelText() << QPoint(hotSpot);

     QMimeData *mimeData = new QMimeData;
     mimeData->setData("application/x-fridgemagnet", itemData);
     mimeData->setText(child->labelText());

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

     child->hide();

     if (drag->exec(Qt::MoveAction | Qt::CopyAction, Qt::CopyAction) == Qt::MoveAction)
         child->close();
     else
         child->show();
 }


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Qt 4.6.3