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sourcewidget.cpp Example File
draganddrop/delayedencoding/sourcewidget.cpp

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 #include <QtGui>
 #include <QtSvg>
 #include "mimedata.h"
 #include "sourcewidget.h"

 SourceWidget::SourceWidget(QWidget *parent)
     : QWidget(parent)
 {
     QFile imageFile(":/images/example.svg");
     imageFile.open(QIODevice::ReadOnly);
     imageData = imageFile.readAll();
     imageFile.close();

     QScrollArea *imageArea = new QScrollArea;
     imageLabel = new QSvgWidget;
     imageLabel->renderer()->load(imageData);
     imageArea->setWidget(imageLabel);
     //imageLabel->setMinimumSize(imageLabel->renderer()->viewBox().size());

     QLabel *instructTopLabel = new QLabel(tr("This is an SVG drawing:"));
     QLabel *instructBottomLabel = new QLabel(
         tr("Drag the icon to copy the drawing as a PNG file:"));
     QPushButton *dragIcon = new QPushButton(tr("Export"));
     dragIcon->setIcon(QIcon(":/images/drag.png"));

     connect(dragIcon, SIGNAL(pressed()), this, SLOT(startDrag()));

     QGridLayout *layout = new QGridLayout;
     layout->addWidget(instructTopLabel, 0, 0, 1, 2);
     layout->addWidget(imageArea, 1, 0, 2, 2);
     layout->addWidget(instructBottomLabel, 3, 0);
     layout->addWidget(dragIcon, 3, 1);
     setLayout(layout);
     setWindowTitle(tr("Delayed Encoding"));
 }

 void SourceWidget::createData(const QString &mimeType)
 {
     if (mimeType != "image/png")
         return;

     QImage image(imageLabel->size(), QImage::Format_RGB32);
     QPainter painter;
     painter.begin(&image);
     imageLabel->renderer()->render(&painter);
     painter.end();

     QByteArray data;
     QBuffer buffer(&data);
     buffer.open(QIODevice::WriteOnly);
     image.save(&buffer, "PNG");
     buffer.close();

     mimeData->setData("image/png", data);
 }

 void SourceWidget::startDrag()
 {
     mimeData = new MimeData;

     connect(mimeData, SIGNAL(dataRequested(const QString &)),
             this, SLOT(createData(const QString &)), Qt::DirectConnection);

     QDrag *drag = new QDrag(this);
     drag->setMimeData(mimeData);
     drag->setPixmap(QPixmap(":/images/drag.png"));

     drag->exec(Qt::CopyAction);
 }