DragDrop problem : QDrag::start doesn't return without mousemove.

[Kratzy974]

Hi

I'm using Drag'n'Drgop with Qt. The drag is started in MouseMove event in one widget. It end in same or other widget. When I release the mouse the DropEvent is called. But sometimes, the QDrag::start doesn't return, when mouse is not moved. Drop is done, Drag does not end.

This seem to happen, when the mouse moved by 1 pix during releasing the mousebutton.
I'm using a code very similar to the example code from the tutorial.

Could anyone help me out here ?

kind regards

[wysota]

Can we see the code?

[Kratzy974]

Here is the code, filled up with some stuff, which isn't needed, but I didn't want to remove stuff, which could be the problem.

//!		This is called, when a Drag'n'Drop is commin into this Widget
//!
void CsfDlg_Overview::dragEnterEvent(QDragEnterEvent *qEvent)
{
	if(!this->mAllowedDropInto)
		qEvent->ignore();
	else if (qEvent->mimeData()->hasFormat(kMime_ThumbOverview.c_str())
		|| qEvent->mimeData()->hasFormat(sfMime_SystemDragDrop.c_str()))
	{
		if ((qEvent->source() == this))
		{
			qEvent->setDropAction(Qt::MoveAction);
			qEvent->accept();
		}
		else
		{
			qEvent->acceptProposedAction();
		}
	}
	else
		qEvent->ignore();
}
 
//!		..when the Drag'n'Drop is moved in this widget
//!
void CsfDlg_Overview::dragMoveEvent(QDragMoveEvent *qEvent)
{
	if(!this->mAllowedDropInto)
		qEvent->ignore();
	else
		emit update();
}
 
//!		Called, when any drag and drop action was ended in this widget
//!
void CsfDlg_Overview::dropEvent(QDropEvent *qEvent)
{
	emit update();
 
	if (!qEvent->mimeData()->hasFormat(kMime_ThumbOverview.c_str())
		&& !qEvent->mimeData()->hasFormat(sfMime_SystemDragDrop.c_str()))
		return;
	if(!this->mAllowedDropInto)
		return;
	if ((qEvent->dropAction() == Qt::MoveAction) || (qEvent->dropAction() == Qt::CopyAction))
		qEvent->acceptProposedAction();
	else
		return;
 
	CsfThumbnailOverview	*thumb(0), thumbTemp;
	if(qEvent->mimeData()->hasFormat(kMime_ThumbOverview.c_str()))
	{
		//	This seem to be a drag drop event from another thumbnail window
		//	The thumbnails are complete in the datastream and need to be read
 
	    QByteArray				itemData(qEvent->mimeData()->data(kMime_ThumbOverview.c_str()));
		QDataStream				dataStream(&itemData, QIODevice::ReadOnly);
		int						quant(0);
		CsfPoint				basePoint, topleftP, curP, hotSpot;
 
		dataStream >> basePoint;
		dataStream >> hotSpot;
		dataStream >> quant;
		if(!this->mReposition)
			topleftP = CsfPoint(qEvent->pos())-hotSpot;
		while(quant > 0)
		{
			dataStream >> thumbTemp;
 
			if(!this->mReposition)
			{
				curP = thumbTemp.getPosition();
				curP -= basePoint;
				curP += topleftP;
				curP += this->mScrollPos;
				thumbTemp.setPosition(curP);
			}
 
			if((this->getThumbnailFromName(thumbTemp.getImageFile()) == NULL) || (qEvent->source() == this))
			{
				thumb = this->addThumbnailToList();
				*thumb = thumbTemp;
				if(!thumb->isThumbnailLowsized())
					thumb->setImageFile(thumb->getImageFile(), true);
			}
			--quant;
		}
		this->slotChangeSizeAbs(this->mThumbSize);
 
		if ((qEvent->source() == this))
		{
			qEvent->setDropAction(Qt::MoveAction);
			qEvent->accept();
		}
		else
			qEvent->acceptProposedAction();
	}
	else if(qEvent->mimeData()->hasFormat(sfMime_SystemDragDrop.c_str()))
	{
		//	This event comes from the desktop an includes just the names of the
		//	files given.
 
		CsfString				strg, ext;
	    QByteArray				itemData(qEvent->mimeData()->data(sfMime_SystemDragDrop.c_str()));
		std::vector<CsfStringA>	filterListIn;
 
		filterListIn = sIMAGEFILELIST.getImageExtensionList();
		QList<QUrl>		urls = qEvent->mimeData()->urls();
		foreach(QUrl url, urls)
		{
			strg = url.toLocalFile();
			if(strg.left(1) == "/")
				strg = strg.right(strg.getLength() - 1);
			//	Sort file out, when the extension is not known
			bool		allowed(false);
			for(std::vector<CsfStringA>::const_iterator iter = filterListIn.begin(); iter != filterListIn.end(); ++iter)
			{
				ext = strg.right((*iter).getLength());
				ext.makeLower();
				if(ext == (*iter))
				{
					allowed = true;
					break;
				}
			}
			if(!allowed)	continue;
			if(this->getThumbnailFromName(strg) == NULL)
			{
				thumb = this->addThumbnailToList();
				thumb->setImageFile(strg);
				if(!this->mReposition)
					thumb->setPosition(CsfPoint(qEvent->pos())+this->mScrollPos);
			}
		}
 
		this->slotChangeSizeAbs(this->mThumbSize);
 
		if ((qEvent->source() == this))
		{
			qEvent->setDropAction(Qt::MoveAction);
			qEvent->accept();
		}
		else
		{
			qEvent->setDropAction(Qt::CopyAction);
			qEvent->accept();
		}
	}
}
 
//********************************************************************************
//	Events commin from using the mouse
//********************************************************************************
 
//!		mouseMoveEvent is called everytime, when the mouse cursor is moved over the window
//!		This method starts the drag/drop if needed and emit an update, when mouse is still clicked.
//!		- Not called after drag/drop started.
void CsfDlg_Overview::mouseMoveEvent(QMouseEvent* qEvent)
{
	QPoint								pt(qEvent->pos());
	std::list<CsfThumbnailOverview*>	activeThumb;;
 
	this->mMouseCurrent = CsfPoint(pt);
 
	while((this->mMouseState &= sfMouseState_Dragging) &&
		(this->mMouseStart.distance(this->mMouseCurrent) > 15.0)) // distance (pixel) when starting the drag/ drop
	{
		//	We need to drag / drop the current thumbnail.
		QDrag			*drag = new QDrag(this);
        QByteArray		itemData;
        QDataStream		dataStream(&itemData, QIODevice::WriteOnly);
        QMimeData		*mimeData = new QMimeData;
		iterator		iter, end;
		CsfRect			rect, thumbRect;
		CsfPoint		point2, point;
 
		end = this->mThumbList.end();
		for(iter = this->mThumbList.begin(); iter != end; ++iter)
		{
			if(iter->getState() == sfMouseState_Dragging)
			{
				activeThumb.clear();
				break;
			}
			if(iter->isThumbnailActive())
			{
				activeThumb.push_back(&(*iter));
				iter->setState(sfMouseState_Dragging);
				if(rect.empty())
					rect = iter->getRect();
				else
					rect.setUnion(rect, iter->getRect());
			}
		}
 
		if(activeThumb.size() == 0)
			break;
 
		//	Painting all thumbnails, wich will be used for drag/drop in an drag/drop image.
		QPixmap			pixmap(rect.width(), rect.height());
		pixmap.fill(QColor(0, 0, 0, 0));
		point = this->mMouseStart - (rect.getTopLeft() - this->mScrollPos);
		point2 = rect.getTopLeft();
		for(std::list<CsfThumbnailOverview*>::iterator iter2 = activeThumb.begin(); iter2 != activeThumb.end(); ++iter2)
		{
			QPainter	painter(&pixmap);
			CsfPoint	whereTo((*iter2)->getRect().getTopLeft() - point2);
 
			painter.drawPixmap(QPoint(whereTo), (*iter2)->getPreRendered());
		}
 
		{	//	The thumbnails need an alpha.
			QPainter	painter(&pixmap);
 
            painter.setCompositionMode(QPainter::CompositionMode_DestinationIn);
            painter.setPen(QColor(255, 255, 255, 120));
            painter.setBrush(QColor(255, 255, 255, 120));
            painter.drawRect(0, 0, pixmap.width(), pixmap.height());
		}
 
		//	Now we savin the thumbnail in the drag / drop.
		dataStream << point2;	// Absolute position, where thumbs were located.
		dataStream << point;	// Hotspot of the drag.
		dataStream << static_cast<int>(activeThumb.size());	// How many thumbnails
		for(std::list<CsfThumbnailOverview*>::iterator iter2 = activeThumb.begin(); iter2 != activeThumb.end(); ++iter2)
		{
			dataStream << *(*iter2);
		}
		mimeData->setData(kMime_ThumbOverview.c_str(), itemData);
 
		drag->setMimeData(mimeData);
		drag->setPixmap(pixmap);
        drag->setHotSpot(point);
 
		Qt::DropAction result = drag->start(Qt::CopyAction | (this->mAllowedDropInto ? Qt::MoveAction : Qt::IgnoreAction));
 
		this->mMouseState &= sfMouseState_Nothing;
 
		if(result == Qt::MoveAction && this->mAllowedDropInto)
		{
			for(std::list<CsfThumbnailOverview*>::iterator iter2 = activeThumb.begin(); iter2 != activeThumb.end(); ++iter2)
			{
				end = this->mThumbList.end();
				for(iter = this->mThumbList.begin(); iter != end; ++iter)
				{
					if(&(*iter) == (*iter2))
					{
						this->mThumbList.erase(iter);
						break;
					}
				}
			}
			this->slotChangeSizeAbs(this->mThumbSize);
		}
 
		end = this->mThumbList.end();
		for(iter = this->mThumbList.begin(); iter != end; ++iter)
			iter->setState(sfMouseState_Nothing);
 
		emit update();	
	}
	if((this->mMouseState & sfMouseState_Clicked))
	{
		emit update();	
	}
}

//!		This is called, when a Drag'n'Drop is commin into this Widget
//!
void CsfDlg_Overview::dragEnterEvent(QDragEnterEvent *qEvent)
{
	if(!this->mAllowedDropInto)
		qEvent->ignore();
	else if (qEvent->mimeData()->hasFormat(kMime_ThumbOverview.c_str())
		|| qEvent->mimeData()->hasFormat(sfMime_SystemDragDrop.c_str()))
	{
		if ((qEvent->source() == this))
		{
			qEvent->setDropAction(Qt::MoveAction);
			qEvent->accept();
		}
		else
		{
			qEvent->acceptProposedAction();
		}
	}
	else
		qEvent->ignore();
}

//!		..when the Drag'n'Drop is moved in this widget
//!
void CsfDlg_Overview::dragMoveEvent(QDragMoveEvent *qEvent)
{
	if(!this->mAllowedDropInto)
		qEvent->ignore();
	else
		emit update();
}

//!		Called, when any drag and drop action was ended in this widget
//!
void CsfDlg_Overview::dropEvent(QDropEvent *qEvent)
{
	emit update();

	if (!qEvent->mimeData()->hasFormat(kMime_ThumbOverview.c_str())
		&& !qEvent->mimeData()->hasFormat(sfMime_SystemDragDrop.c_str()))
		return;
	if(!this->mAllowedDropInto)
		return;
	if ((qEvent->dropAction() == Qt::MoveAction) || (qEvent->dropAction() == Qt::CopyAction))
		qEvent->acceptProposedAction();
	else
		return;

	CsfThumbnailOverview	*thumb(0), thumbTemp;
	if(qEvent->mimeData()->hasFormat(kMime_ThumbOverview.c_str()))
	{
		//	This seem to be a drag drop event from another thumbnail window
		//	The thumbnails are complete in the datastream and need to be read

	    QByteArray				itemData(qEvent->mimeData()->data(kMime_ThumbOverview.c_str()));
		QDataStream				dataStream(&itemData, QIODevice::ReadOnly);
		int						quant(0);
		CsfPoint				basePoint, topleftP, curP, hotSpot;

		dataStream >> basePoint;
		dataStream >> hotSpot;
		dataStream >> quant;
		if(!this->mReposition)
			topleftP = CsfPoint(qEvent->pos())-hotSpot;
		while(quant > 0)
		{
			dataStream >> thumbTemp;
			
			if(!this->mReposition)
			{
				curP = thumbTemp.getPosition();
				curP -= basePoint;
				curP += topleftP;
				curP += this->mScrollPos;
				thumbTemp.setPosition(curP);
			}

			if((this->getThumbnailFromName(thumbTemp.getImageFile()) == NULL) || (qEvent->source() == this))
			{
				thumb = this->addThumbnailToList();
				*thumb = thumbTemp;
				if(!thumb->isThumbnailLowsized())
					thumb->setImageFile(thumb->getImageFile(), true);
			}
			--quant;
		}
		this->slotChangeSizeAbs(this->mThumbSize);

		if ((qEvent->source() == this))
		{
			qEvent->setDropAction(Qt::MoveAction);
			qEvent->accept();
		}
		else
			qEvent->acceptProposedAction();
	}
	else if(qEvent->mimeData()->hasFormat(sfMime_SystemDragDrop.c_str()))
	{
		//	This event comes from the desktop an includes just the names of the
		//	files given.

		CsfString				strg, ext;
	    QByteArray				itemData(qEvent->mimeData()->data(sfMime_SystemDragDrop.c_str()));
		std::vector<CsfStringA>	filterListIn;

		filterListIn = sIMAGEFILELIST.getImageExtensionList();
		QList<QUrl>		urls = qEvent->mimeData()->urls();
		foreach(QUrl url, urls)
		{
			strg = url.toLocalFile();
			if(strg.left(1) == "/")
				strg = strg.right(strg.getLength() - 1);
			//	Sort file out, when the extension is not known
			bool		allowed(false);
			for(std::vector<CsfStringA>::const_iterator iter = filterListIn.begin(); iter != filterListIn.end(); ++iter)
			{
				ext = strg.right((*iter).getLength());
				ext.makeLower();
				if(ext == (*iter))
				{
					allowed = true;
					break;
				}
			}
			if(!allowed)	continue;
			if(this->getThumbnailFromName(strg) == NULL)
			{
				thumb = this->addThumbnailToList();
				thumb->setImageFile(strg);
				if(!this->mReposition)
					thumb->setPosition(CsfPoint(qEvent->pos())+this->mScrollPos);
			}
		}

		this->slotChangeSizeAbs(this->mThumbSize);

		if ((qEvent->source() == this))
		{
			qEvent->setDropAction(Qt::MoveAction);
			qEvent->accept();
		}
		else
		{
			qEvent->setDropAction(Qt::CopyAction);
			qEvent->accept();
		}
	}
}

//********************************************************************************
//	Events commin from using the mouse
//********************************************************************************

//!		mouseMoveEvent is called everytime, when the mouse cursor is moved over the window
//!		This method starts the drag/drop if needed and emit an update, when mouse is still clicked.
//!		- Not called after drag/drop started.
void CsfDlg_Overview::mouseMoveEvent(QMouseEvent* qEvent)
{
	QPoint								pt(qEvent->pos());
	std::list<CsfThumbnailOverview*>	activeThumb;;

	this->mMouseCurrent = CsfPoint(pt);

	while((this->mMouseState &= sfMouseState_Dragging) &&
		(this->mMouseStart.distance(this->mMouseCurrent) > 15.0)) // distance (pixel) when starting the drag/ drop
	{
		//	We need to drag / drop the current thumbnail.
		QDrag			*drag = new QDrag(this);
        QByteArray		itemData;
        QDataStream		dataStream(&itemData, QIODevice::WriteOnly);
        QMimeData		*mimeData = new QMimeData;
		iterator		iter, end;
		CsfRect			rect, thumbRect;
		CsfPoint		point2, point;

		end = this->mThumbList.end();
		for(iter = this->mThumbList.begin(); iter != end; ++iter)
		{
			if(iter->getState() == sfMouseState_Dragging)
			{
				activeThumb.clear();
				break;
			}
			if(iter->isThumbnailActive())
			{
				activeThumb.push_back(&(*iter));
				iter->setState(sfMouseState_Dragging);
				if(rect.empty())
					rect = iter->getRect();
				else
					rect.setUnion(rect, iter->getRect());
			}
		}

		if(activeThumb.size() == 0)
			break;

		//	Painting all thumbnails, wich will be used for drag/drop in an drag/drop image.
		QPixmap			pixmap(rect.width(), rect.height());
		pixmap.fill(QColor(0, 0, 0, 0));
		point = this->mMouseStart - (rect.getTopLeft() - this->mScrollPos);
		point2 = rect.getTopLeft();
		for(std::list<CsfThumbnailOverview*>::iterator iter2 = activeThumb.begin(); iter2 != activeThumb.end(); ++iter2)
		{
			QPainter	painter(&pixmap);
			CsfPoint	whereTo((*iter2)->getRect().getTopLeft() - point2);

			painter.drawPixmap(QPoint(whereTo), (*iter2)->getPreRendered());
		}

		{	//	The thumbnails need an alpha.
			QPainter	painter(&pixmap);

            painter.setCompositionMode(QPainter::CompositionMode_DestinationIn);
            painter.setPen(QColor(255, 255, 255, 120));
            painter.setBrush(QColor(255, 255, 255, 120));
            painter.drawRect(0, 0, pixmap.width(), pixmap.height());
		}

		//	Now we savin the thumbnail in the drag / drop.
		dataStream << point2;	// Absolute position, where thumbs were located.
		dataStream << point;	// Hotspot of the drag.
		dataStream << static_cast<int>(activeThumb.size());	// How many thumbnails
		for(std::list<CsfThumbnailOverview*>::iterator iter2 = activeThumb.begin(); iter2 != activeThumb.end(); ++iter2)
		{
			dataStream << *(*iter2);
		}
		mimeData->setData(kMime_ThumbOverview.c_str(), itemData);

		drag->setMimeData(mimeData);
		drag->setPixmap(pixmap);
        drag->setHotSpot(point);

		Qt::DropAction result = drag->start(Qt::CopyAction | (this->mAllowedDropInto ? Qt::MoveAction : Qt::IgnoreAction));

		this->mMouseState &= sfMouseState_Nothing;

		if(result == Qt::MoveAction && this->mAllowedDropInto)
		{
			for(std::list<CsfThumbnailOverview*>::iterator iter2 = activeThumb.begin(); iter2 != activeThumb.end(); ++iter2)
			{
				end = this->mThumbList.end();
				for(iter = this->mThumbList.begin(); iter != end; ++iter)
				{
					if(&(*iter) == (*iter2))
					{
						this->mThumbList.erase(iter);
						break;
					}
				}
			}
			this->slotChangeSizeAbs(this->mThumbSize);
		}

		end = this->mThumbList.end();
		for(iter = this->mThumbList.begin(); iter != end; ++iter)
			iter->setState(sfMouseState_Nothing);

		emit update();	
	}
	if((this->mMouseState & sfMouseState_Clicked))
	{
		emit update();	
	}
}

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