QT Drag and Drop a QLabel into a QGraphicsView, how to?

[jiapei100]

Hi, all:

Sorry to bug you once again.

I'm trying to drag and drop a QLabel into a QGraphicsView.

My inherited label class looks like:

class CQtShapesLabel : public QLabel
{
Q_OBJECT
 
 
public:
 
 
explicit CQtShapesLabel(QWidget *parent = 0, int type = 0) : QLabel(parent), m_iType(type)
{
// this->m_qMimeData = NULL;
// this->m_qDrag = NULL;
}
 
 
virtual ~CQtShapesLabel() {}
 
 
protected:
// void dragEnterEvent(QDragEnterEvent *event);
// void dragMoveEvent(QDragMoveEvent *event);
void mousePressEvent(QMouseEvent *event);
void mouseReleaseEvent(QMouseEvent *event);
 
 
private:
// QMimeData* m_qMimeData;
// QDrag * m_qDrag;
int m_iType;
};

class CQtShapesLabel : public QLabel
{
Q_OBJECT


public:


explicit CQtShapesLabel(QWidget *parent = 0, int type = 0) : QLabel(parent), m_iType(type)
{
// this->m_qMimeData = NULL;
// this->m_qDrag = NULL;
}


virtual ~CQtShapesLabel() {}


protected:
// void dragEnterEvent(QDragEnterEvent *event);
// void dragMoveEvent(QDragMoveEvent *event);
void mousePressEvent(QMouseEvent *event);
void mouseReleaseEvent(QMouseEvent *event);


private:
// QMimeData* m_qMimeData;
// QDrag * m_qDrag;
int m_iType;
};

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and mousePressEvent() function is defined as:

void CQtShapesLabel::mousePressEvent(QMouseEvent *event)
{
    QPixmap pixmap = *this->pixmap();
 
    QByteArray itemData;
    QDataStream dataStream(&itemData, QIODevice::WriteOnly);
    dataStream << pixmap << QPoint(event->pos());
 
    QMimeData* m_qMimeData = new QMimeData;
    m_qMimeData->setData("application/x-dnditemdata", itemData);
 
    QDrag* m_qDrag = new QDrag(this);
    m_qDrag->setMimeData(m_qMimeData);
    m_qDrag->setPixmap(pixmap);
    m_qDrag->setHotSpot(event->pos());
 
    QPixmap tempPixmap = pixmap;
    QPainter painter;
    painter.begin(&tempPixmap);
    painter.fillRect(pixmap.rect(), QColor(127, 127, 127, 127));
    painter.end();
 
    this->setPixmap(tempPixmap);
 
    if (m_qDrag->exec(Qt::CopyAction | Qt::MoveAction, Qt::CopyAction) == Qt::MoveAction)
        this->close();
    else
    {
        this->show();
        this->setPixmap(pixmap);
    }
}

void CQtShapesLabel::mousePressEvent(QMouseEvent *event)
{
    QPixmap pixmap = *this->pixmap();

    QByteArray itemData;
    QDataStream dataStream(&itemData, QIODevice::WriteOnly);
    dataStream << pixmap << QPoint(event->pos());

    QMimeData* m_qMimeData = new QMimeData;
    m_qMimeData->setData("application/x-dnditemdata", itemData);

    QDrag* m_qDrag = new QDrag(this);
    m_qDrag->setMimeData(m_qMimeData);
    m_qDrag->setPixmap(pixmap);
    m_qDrag->setHotSpot(event->pos());

    QPixmap tempPixmap = pixmap;
    QPainter painter;
    painter.begin(&tempPixmap);
    painter.fillRect(pixmap.rect(), QColor(127, 127, 127, 127));
    painter.end();

    this->setPixmap(tempPixmap);

    if (m_qDrag->exec(Qt::CopyAction | Qt::MoveAction, Qt::CopyAction) == Qt::MoveAction)
        this->close();
    else
    {
        this->show();
        this->setPixmap(pixmap);
    }
}

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My inherited QGraphicsView class looks like:

class QTVIEWS_EXPORT CImageView : public QGraphicsView
{
Q_OBJECT
 
 
 
 
protected:
//void paintEvent(QPaintEvent *event);
void dragEnterEvent(QDragEnterEvent *event);
void dragMoveEvent(QDragMoveEvent *event);
void dragLeaveEvent(QDragLeaveEvent *event);
void dropEvent(QDropEvent *event);
// void mousePressEvent(QMouseEvent *event);
 
 
 
 
public:
 
 
CImageView( QWidget *parent = 0, unsigned int idx = 0 );
virtual ~CImageView( );
 
 
};

class QTVIEWS_EXPORT CImageView : public QGraphicsView
{
Q_OBJECT




protected:
//void paintEvent(QPaintEvent *event);
void dragEnterEvent(QDragEnterEvent *event);
void dragMoveEvent(QDragMoveEvent *event);
void dragLeaveEvent(QDragLeaveEvent *event);
void dropEvent(QDropEvent *event);
// void mousePressEvent(QMouseEvent *event);




public:


CImageView( QWidget *parent = 0, unsigned int idx = 0 );
virtual ~CImageView( );


};

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When testing, I tried to print out something in all functions, but no matter how I tried, I found

CQtShapesLabel::mouseReleaseEvent(QMouseEvent*event); // understandable
CImageView::dragLeaveEvent(QDragLeaveEvent*event); // should be able to response when the drag leaves this view
CImageView::dropEvent(QDropEvent*event); // should be able to response when the drag tries to drop something
CImageView::dragMoveEvent(QDragMoveEvent*event) // should be able to response when the drag keeps moving inside the view

never responses. Why is it so? Can anybody help to explain please....


Best Regards
Pei

[wysota]

What about dragEnterEvent?

[thomas@itest]

from the doc : if(QGraphicsView::dragMode() == QGraphicsView::NoDrag) Nothing happens; the mouse event is ignored.

[jiapei100]

dragEnterEvent works perfectly here.

What about dragEnterEvent?

[wysota]

dragEnterEvent works perfectly here.

Do you accept the event in dragEnterEvent? If the event is accepted, does dragMoveEvent work? For other drag events to work, you need to accept a dragEnterEvent.

[jiapei100]

Wow... Thank you so much wysota.
You are always able to answer my questions !! After accept the dragEnterEvent, everything is working fine now !!!


Thank you so much !!


Best Regards
Pei

Do you accept the event in dragEnterEvent? If the event is accepted, does dragMoveEvent work? For other drag events to work, you need to accept a dragEnterEvent.