#include <QtCore>
#include <QtGui>
#include <QtWidgets>

class MyWidget : public QLabel
{
public:
    MyWidget(): QLabel(0)
    {
        setMinimumSize(QSize(200, 200));
        setAcceptDrops(true);
    }

protected:
    virtual void dropEvent(QDropEvent* event)
    {
        const QMimeData* mimeData = event->mimeData();
        qDebug() << "allFormats:" << mimeData->formats();
        const QString mime = "image/png";

        const QByteArray data = mimeData->data(mime);
        if(data.isEmpty()) {
            qWarning("Bug: image/png data is not available when the drag is from the same process!");
        }

        QPixmap pix;
        if (!pix.loadFromData(data))
        qWarning("loading failed");
        setPixmap(pix);
        event->acceptProposedAction();
    }

    virtual void dragEnterEvent(QDragEnterEvent* event)
    {
        event->accept();
    }

    virtual void dragMoveEvent(QDragMoveEvent* event)
    {
        event->accept();
    }

    virtual void mouseMoveEvent(QMouseEvent*)
    {
        QDrag* drag = new QDrag(this);
        QMimeData* mimeData = new QMimeData;
        mimeData->setText(text());
        QImage img("mail-message.png");
        Q_ASSERT(!img.isNull());
        mimeData->setImageData(img);
        drag->setPixmap(QPixmap::fromImage(img));
        drag->setMimeData(mimeData);
        drag->exec();
    }
};

int main( int argc, char ** argv )
{
    QApplication app(argc, argv);
    MyWidget w1;
    w1.setText("Please drag from this widget");
    w1.show();
    MyWidget w2;
    w2.setText("Drop here");
    w2.show();
    return app.exec();
}