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;
};@

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&#40;Qt::CopyAction | Qt::MoveAction, Qt::CopyAction&#41; == Qt::MoveAction)
    this->close();
else
{
    this->show();
    this->setPixmap(pixmap);
}

}@

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( );

};@

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

bq. 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

SGaist

Hi,

Did you "setAcceptDrops(true)" in your CImageView ?

Code_ReaQtor

Sorry but it is not really clear how you implemented receiving the "drops" - you only show what was in the header file of your subclassed QGraphicsView.

Anyways, if you actually want to drag and drop a QWidget (QLabel, etc) into a QGraphicsView/Scene, you need to use "QGraphicsProxyWidget":http://qt-project.org/doc/qt-4.8/qgraphicsproxywidget.html

Also, some devs, most of the time, forgets to enable "setAcceptDrops":http://doc-snapshot.qt-project.org/4.8/qwidget.html#acceptDrops-prop

jiapei100

Yes, I do have setAcceptDrops(true); in my code, which is the first line of CImageView constructor, before
@ ......
this->setScene( this->m_QTGraphicsScene );
this->show();@

[quote author="SGaist" date="1362479189"]Hi,

Did you "setAcceptDrops(true)" in your CImageView ?[/quote]

Sam

Hi,

I hope that you are checking the mimeData format in each of the drag funcions like

@void CImageView::dragEnterEvent(QDragEnterEvent *event)
{
if (event->mimeData()->hasFormat("application/x-dnditemdata"))
{
event->accept();
} else
{
event->ignore();
}
}@

Can you share the code of CImageView class , that will give the exact picture of your implementation.

jiapei100

Some more code is provided now:

VO_ImageView.h
@
#ifndef VO_IMAGEVIEW_H
#define VO_IMAGEVIEW_H

#include "qtviews_global.h"

#include <QGraphicsView>
#include <QGraphicsPixmapItem>
#include <QGraphicsItem>
#include <QGraphicsLineItem>
#include <QGraphicsItemGroup>
#include <QLabel>
#include <QBoxLayout>
#include <QMouseEvent>

using namespace std;

/**
show an image in the corresponding QGraphicsView
*/
class QTVIEWS_EXPORT CImageView : public QGraphicsView
{
Q_OBJECT

private:
int m_iIdx;
QGraphicsScene* m_QTGraphicsScene;
QPixmap* m_QTBackGroundPixmap;
QGraphicsPixmapItem* m_QTBackGroundItem;

void init()
{
this->m_QTGraphicsScene = NULL;
this->m_QTBackGroundPixmap = NULL;
this->m_QTBackGroundItem = NULL;
setAcceptDrops(true);
}

protected:
void dragEnterEvent(QDragEnterEvent *event);
void dragMoveEvent(QDragMoveEvent *event);
void dropEvent(QDropEvent *event);

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

#endif
@

VO_ImageView.cpp
@
#include <QBuffer>

// main header
#include "VO_ImageView.h"
#include "LV_QtShapesLabel.h"

CImageView::CImageView(QWidget *parent, unsigned int idx): QGraphicsView(parent), m_iIdx(idx)
{
this->init();
this->m_QTGraphicsScene = new QGraphicsScene;
this->m_QTBackGroundItem = new QGraphicsPixmapItem;
this->setHorizontalScrollBarPolicy ( Qt::ScrollBarAlwaysOff );
this->setVerticalScrollBarPolicy ( Qt::ScrollBarAlwaysOff );
this->setScene( this->m_QTGraphicsScene );
this->show();
this->m_QTBackGroundPixmap = new QPixmap( 320, 240);
this->m_QTBackGroundItem->setPixmap ( *this->m_QTBackGroundPixmap );
this->m_QTGraphicsScene->addItem(this->m_QTBackGroundItem);
}

CImageView::~CImageView( )
{
if(this->m_QTBackGroundPixmap) delete (this->m_QTBackGroundPixmap);
if(this->m_QTGraphicsScene) delete (this->m_QTGraphicsScene);
}

void CImageView::dragEnterEvent(QDragEnterEvent event)
{
if (event->mimeData()->hasFormat("application/x-dnditemdata"))
{
switch( dynamic_cast<CQtShapesLabel>(event->source())->getType() )
{
case CQtShapesLabel::SPHERE:
cout << "SPHERE" << endl;
break;
case CQtShapesLabel::CUBE:
cout << "CUBOID" << endl;
break;
case CQtShapesLabel::CUBOID:
cout << "CUBOID" << endl;
break;
case CQtShapesLabel::CYLINDER:
cout << "CONE" << endl;
break;
case CQtShapesLabel::HEXAGONALPRISM:
cout << "PYRAMID" << endl;
break;
case CQtShapesLabel::CONE:
cout << "CONUS" << endl;
break;
case CQtShapesLabel::SQUAREBASEDPYRAMID:
cout << "CYLINDER" << endl;
break;
case CQtShapesLabel::TRIANGULARBASEDPYRAMID:
cout << "SPHERE" << endl;
break;
case CQtShapesLabel::TRIANGULARPRISM:
cout << "SPHERE" << endl;
break;
case CQtShapesLabel::CIRCLE:
cout << "CIRCLE" << endl;
break;
case CQtShapesLabel::OVAL:
cout << "OVAL" << endl;
break;
case CQtShapesLabel::TRIANGLE:
cout << "TRIANGLE" << endl;
break;
case CQtShapesLabel::SQUARE:
cout << "SQUARE" << endl;
break;
case CQtShapesLabel::RECTANGLE:
cout << "RECTANGLE" << endl;
break;
case CQtShapesLabel::RHOMBUS:
cout << "RHOMBUS" << endl;
break;
case CQtShapesLabel::TRAPEZOID:
cout << "TRAPEZOID" << endl;
break;
case CQtShapesLabel::SHAPE3D:
default:
event->ignore();
break;
}
}
else
{
event->ignore();
}
}

void CImageView::dragMoveEvent(QDragMoveEvent *event)
{
if (event->mimeData()->hasFormat("application/x-dnditemdata"))
{
event->accept();
int aaa = 9999;
cout << aaa << endl;
} else
{
event->ignore();
}
}

void CImageView::dropEvent(QDropEvent *event)
{
if (event->mimeData()->hasFormat("application/x-dnditemdata"))
{
event->accept();
int aaa = 44444444;
cout << aaa << endl;
} else
{
event->ignore();
}
}
@

jiapei100

Hi, thank you for your reply. I don't want to drag and drop a QWidget, but I want to draw a shape onto QGraphicsView when I drop the QLabel on the QGraphicsView. And I'm expecting the shape to be able to be modified/changed after a further drag within the QGraphicsView.

Any demos?

Cheers
Pei

[quote author="Code_ReaQtor" date="1362479727"]Sorry but it is not really clear how you implemented receiving the "drops" - you only show what was in the header file of your subclassed QGraphicsView.

Anyways, if you actually want to drag and drop a QWidget (QLabel, etc) into a QGraphicsView/Scene, you need to use "QGraphicsProxyWidget":http://qt-project.org/doc/qt-4.8/qgraphicsproxywidget.html

Also, some devs, most of the time, forgets to enable "setAcceptDrops":http://doc-snapshot.qt-project.org/4.8/qwidget.html#acceptDrops-prop[/quote]

[quote author="Code_ReaQtor" date="1362479727"]Sorry but it is not really clear how you implemented receiving the "drops" - you only show what was in the header file of your subclassed QGraphicsView.

Anyways, if you actually want to drag and drop a QWidget (QLabel, etc) into a QGraphicsView/Scene, you need to use "QGraphicsProxyWidget":http://qt-project.org/doc/qt-4.8/qgraphicsproxywidget.html

Also, some devs, most of the time, forgets to enable "setAcceptDrops":http://doc-snapshot.qt-project.org/4.8/qwidget.html#acceptDrops-prop[/quote]

Sam

Hi,

I tested your aplication and it works as required. The problem is that in your dragEnterEvent() you are not using
event->accept() anywhere, try to add the same and run again.

Code_ReaQtor

[quote author="jiapei100" date="1362553970"]
I don't want to drag and drop a QWidget, but I want to draw a shape onto QGraphicsView when I drop the QLabel on the QGraphicsView.
[/quote]

When dropped, it should be changed into a QGraphicsItem.

I can't really see some major problems (or I am just missing something). Keep in mind to check the following using cout/qDebug/etc:

check if setAcceptDrops is set to true

check if "dynamic_cast" worked

are you using "enum" with these? CQtShapesLabel::SPHERE, CQtShapesLabel::CUBE, etc.... since I can't see them implemented in the code

jiapei100

You are right Sam... Thank you so much !!

[quote author="Sam" date="1362568332"]Hi,

I tested your aplication and it works as required. The problem is that in your dragEnterEvent() you are not using
event->accept() anywhere, try to add the same and run again.

[/quote]

Sam

[quote author="jiapei100" date="1362607972"]
You are right Sam... Thank you so much !!

[quote author="Sam" date="1362568332"]Hi,

I tested your aplication and it works as required. The problem is that in your dragEnterEvent() you are not using
event->accept() anywhere, try to add the same and run again.

[/quote]

You are welcome :)