Drag and Drop, dropEvent not being called?

[steg90]

got it - setSupportedDragActions !

mimeTypes gets called but dropMimeData and mimeData are not...

[jpn]

Do you return drag and drop flags in flags()?

[steg90]

Hi JPN,

I have the following flags function in my model code :

Qt::ItemFlags DACanTreeModel::flags(const QModelIndex &index) const
{
	Qt::ItemFlags defaultFlags = QAbstractTableModel::flags(index);
	if (index.isValid())
         return Qt::ItemIsDragEnabled | Qt::ItemIsDropEnabled | defaultFlags;	
	else
		return Qt::ItemIsDropEnabled | defaultFlags;
}

Qt::ItemFlags DACanTreeModel::flags(const QModelIndex &index) const
{
	Qt::ItemFlags defaultFlags = QAbstractTableModel::flags(index);
	if (index.isValid())
         return Qt::ItemIsDragEnabled | Qt::ItemIsDropEnabled | defaultFlags;	
	else
		return Qt::ItemIsDropEnabled | defaultFlags;
}

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Still can't get the dropMimeData function to be called...

[steg90]

Also, the flags for the item in the treewidget I'm dragging are set to ItemIsDragEnabled. Can't understand why dropMimeData isn't being called...

Regards,
Steve

[wysota]

Also if you drag between two widgets, make sure they understand each other's mime-types.

[jpn]

Presumably you are already following the instructions in Using Drag and Drop with Item Views, because your flags() looks so similar. But does your view still have overridden drag/dragmove/drop event handlers? If so, I'd suggest commenting them out. For example accepting the event in dropEvent() and then calling the base class implementation makes it never drop..

[steg90]

Hi,

Yes, following that example, I had removed the events from my view. Still not being called, got to be something simple?!

This is the code I have in my treewidget ( items in here I want to be draggable ) :

void DASignalTree::mousePressEvent ( QMouseEvent * event )
{
	if( event->button() == Qt::LeftButton )
	{
		m_startPos = event->pos();
	}
	QTreeWidget::mousePressEvent( event );
}
 
void DASignalTree::mouseMoveEvent( QMouseEvent * event )
{
	if( event->buttons() & Qt::LeftButton ) 
	{
		int distance = ( event->pos() - m_startPos).manhattanLength();
		if( distance >= QApplication::startDragDistance() )
		{
			QTreeWidgetItem *item = itemAt( m_startPos );
			if ( item ) 
			{
				startDrag(); 
			}
		}
	}
//	QTreeWidget::mouseMoveEvent( event );
}
 
void DASignalTree::startDrag()
{
	QTreeWidgetItem* dragItem = currentItem();
	DAMimeData* pMimeData = new DAMimeData;
	pMimeData->setText( dragItem->text( 0 ) );
	QDrag* pDrag = new QDrag( this );
	pDrag->setMimeData( pMimeData );
	pDrag->setPixmap( QPixmap("images/new.png") );
 
	theApp->AddText( dragItem->text( 0 ) );
 
	if( pDrag->start(Qt::MoveAction) == Qt::MoveAction)
		delete dragItem;
}

void DASignalTree::mousePressEvent ( QMouseEvent * event )
{
	if( event->button() == Qt::LeftButton )
	{
		m_startPos = event->pos();
	}
	QTreeWidget::mousePressEvent( event );
}

void DASignalTree::mouseMoveEvent( QMouseEvent * event )
{
	if( event->buttons() & Qt::LeftButton ) 
	{
		int distance = ( event->pos() - m_startPos).manhattanLength();
		if( distance >= QApplication::startDragDistance() )
		{
			QTreeWidgetItem *item = itemAt( m_startPos );
			if ( item ) 
			{
				startDrag(); 
			}
		}
	}
//	QTreeWidget::mouseMoveEvent( event );
}

void DASignalTree::startDrag()
{
	QTreeWidgetItem* dragItem = currentItem();
	DAMimeData* pMimeData = new DAMimeData;
	pMimeData->setText( dragItem->text( 0 ) );
	QDrag* pDrag = new QDrag( this );
	pDrag->setMimeData( pMimeData );
	pDrag->setPixmap( QPixmap("images/new.png") );

	theApp->AddText( dragItem->text( 0 ) );

	if( pDrag->start(Qt::MoveAction) == Qt::MoveAction)
		delete dragItem;
}

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and the code in my model :

bool DACanTreeModel::dropMimeData ( const QMimeData * data, Qt::DropAction action, int row, int column, const QModelIndex & parent )
{
	return true;
}
 
QStringList DACanTreeModel::mimeTypes () const
{
	return QStringList();
}
 
QMimeData * DACanTreeModel::mimeData ( const QModelIndexList & indexes ) const
{
	return new QMimeData();
}
 
 
Qt::DropActions DACanTreeModel::supportedDropActions() const
{
	return Qt::CopyAction | Qt::MoveAction;
}
 
Qt::ItemFlags DACanTreeModel::flags(const QModelIndex &index) const
{
	Qt::ItemFlags defaultFlags = QAbstractTableModel::flags(index);
	if (index.isValid())
         return Qt::ItemIsDragEnabled | Qt::ItemIsDropEnabled | defaultFlags;	
	else
		return Qt::ItemIsDropEnabled | defaultFlags;
}

bool DACanTreeModel::dropMimeData ( const QMimeData * data, Qt::DropAction action, int row, int column, const QModelIndex & parent )
{
	return true;
}

QStringList DACanTreeModel::mimeTypes () const
{
	return QStringList();
}

QMimeData * DACanTreeModel::mimeData ( const QModelIndexList & indexes ) const
{
	return new QMimeData();
}


Qt::DropActions DACanTreeModel::supportedDropActions() const
{
	return Qt::CopyAction | Qt::MoveAction;
}

Qt::ItemFlags DACanTreeModel::flags(const QModelIndex &index) const
{
	Qt::ItemFlags defaultFlags = QAbstractTableModel::flags(index);
	if (index.isValid())
         return Qt::ItemIsDragEnabled | Qt::ItemIsDropEnabled | defaultFlags;	
	else
		return Qt::ItemIsDropEnabled | defaultFlags;
}

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And finally the view constructor :

DATableView::DATableView(QWidget *parent)
	: QTableView(parent)
{
	setAcceptDrops(true);
	setDropIndicatorShown(true);
}

DATableView::DATableView(QWidget *parent)
	: QTableView(parent)
{
	setAcceptDrops(true);
	setDropIndicatorShown(true);
}

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I'm at a loss?!

Regards,
Steve

[wysota]

The tree widget also has the before mentioned methods which you should reimplement.

[steg90]

Thanks,

So I need to also implement dropMimeData, mimeData and mimeTypes in my tree widget? I guess I can ignore the dropMimeData as my tree won't allow any drop events?

Regards,
Steve

[steg90]

Implemented the methods mimeData, dropmimeData and mimeTypes in the tree widget, but still no dropMimeData being called...

When I was doing the drag/drop in the view, it seemed a lot easier and seemed to work, just can't understand what is wrong.

Regards,
Steve

[wysota]

Here is a working example.

[steg90]

Many thanks, that is very kind of you.

[steg90]

Many thanks for the example, I think way back in the thread or a related one you did mention that you should only implement the dropMimeData, mimeData and mimeTypes functions, I should have listened!!! I had implemented a few mouse event functions and a few drag events in my tree widget which I shouldn't have done, this was stopping it working.

Is it possible to pass over the object associated with the item being dragged from the tree widget?

Kind regards,
Steve

[wysota]

Many thanks for the example, I think way back in the thread or a related one you did mention that you should only implement the dropMimeData, mimeData and mimeTypes functions, I should have listened!!! I had implemented a few mouse event functions and a few drag events in my tree widget which I shouldn't have done, this was stopping it working.

I think we told you a few times to remove the mouse event handlers

Is it possible to pass over the object associated with the item being dragged from the tree widget?

In general, yes. You can pass a pointer or something like that, you can subclass QMimeData if you want. But the proper way to go would be to serialize your object to QByteArray, transfer that array using QMimeData::setData and reconstruct the object on the other side.