Qt实现不同Treewidget之间拖拽

拖拽是编程中经常要用到的，我这里主要是实习了Treewidget之间直接拖拽Item，按下Ctrl键的话是copy，不按Ctrl则是Move。以下是实现代码

class TreeItemMimeData:public QMimeData
{
	Q_OBJECT
public:
	TreeItemMimeData():QMimeData()
	{
		m_pDragItem = NULL;
	}

	~TreeItemMimeData()
	{

	}

	void SetDragData(QString mimeType , QTreeWidgetItem *pItem)
	{
		m_format<<mimeType;
		m_pDragItem = pItem;
	}
	


	QStringList formats() const
	{
		return m_format;
	}

	const QTreeWidgetItem* DragItemData() const
	{
		return m_pDragItem;
	}


protected:

	QVariant retrieveData(const QString &mimetype, QVariant::Type preferredType) const
	{
		if (mimetype == "ItemMimeData")
		{
			return m_pDragItem;
		}
		else
		{
			 return QMimeData::retrieveData(mimetype, preferredType);  
		}
	}
private:
	const QTreeWidgetItem   *m_pDragItem;
	QStringList              m_format;
};

class MyTreeWidget:public QTreeWidget
{
	Q_OBJECT
public:
	MyTreeWidget(QWidget *parent = NULL);
	~MyTreeWidget();

protected:
	void mouseMoveEvent(QMouseEvent *event);
	void mousePressEvent(QMouseEvent *event);
	void mouseReleaseEvent(QMouseEvent *event);

	void dragEnterEvent(QDragEnterEvent *event);
	void dragMoveEvent(QDragMoveEvent *event);
	void dropEvent(QDropEvent *event);
	void keyPressEvent(QKeyEvent *event);
	void keyReleaseEvent(QKeyEvent *event);
private:
	QPoint     m_startDragPoint;
	void       performDrag();
	bool       m_CtrlPressed;

};

MyTreeWidget::MyTreeWidget(QWidget *parent /*= NULL*/):QTreeWidget(parent)
{
	m_CtrlPressed = false;
	this->setSelectionMode(QAbstractItemView::ExtendedSelection);
	this->setAcceptDrops(true);
	this->setDragEnabled(true);
	this->setStyleSheet("QTreeWidget::item:selected{ background-color: rgb(150, 0, 0)}");
}

MyTreeWidget::~MyTreeWidget()
{
}

void MyTreeWidget::keyPressEvent(QKeyEvent *event)
{
	if (event->key() == Qt::Key_Control)
	{
		m_CtrlPressed = true;
	}
}

void MyTreeWidget::keyReleaseEvent(QKeyEvent *event)
{
	if (event->key() == Qt::Key_Control)
	{
		m_CtrlPressed = false;
	}
}

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

void MyTreeWidget::mouseMoveEvent(QMouseEvent *event)
{
	if (event->buttons() & Qt::LeftButton)
	{
		int dragDistance = (event->pos() - m_startDragPoint).manhattanLength();
		if (dragDistance > QApplication::startDragDistance())
		{
			performDrag();
		}
	}
	QTreeWidget::mouseMoveEvent(event);

}

void MyTreeWidget::mouseReleaseEvent(QMouseEvent *event)
{
	QTreeWidget::mouseReleaseEvent(event);
}

void MyTreeWidget::dragEnterEvent(QDragEnterEvent *event)
{
	QWidget *source =  qobject_cast<MyTreeWidget *>(event->source());  
	if (source /*&& source != this*/) 
	{  
		if (m_CtrlPressed)
		{
			event->setDropAction(Qt::CopyAction);  
		} 
		else
		{
			event->setDropAction(Qt::MoveAction);  
		}
		/*event->setDropAction(Qt::MoveAction);  */
		event->accept();  
	}  
}

void MyTreeWidget::dragMoveEvent(QDragMoveEvent *event)
{

	QWidget *source =  qobject_cast<MyTreeWidget *>(event->source());  
	if (source /*&& source != this*/)
	{  
		const TreeItemMimeData *pMimeData = (const TreeItemMimeData *)(event->mimeData()); 
		const QTreeWidgetItem *item = pMimeData->DragItemData();
		QTreeWidgetItem *currentItem = this->itemAt(event->pos());
		if (currentItem == item)           //不允许拖回到原来的item
		{
			event->ignore();
		} 
		else
		{
			setCurrentItem(currentItem);
			if (m_CtrlPressed)
			{
				event->setDropAction(Qt::CopyAction);  
			} 
			else
			{
				event->setDropAction(Qt::MoveAction);  
			}
			//event->setDropAction(Qt::MoveAction);  
			event->accept();  
		}
		
	}  
}

void MyTreeWidget::dropEvent(QDropEvent *event)
{
	QWidget *source =  qobject_cast<MyTreeWidget *>(event->source()); 
	const TreeItemMimeData *pMimeData = (const TreeItemMimeData *)(event->mimeData()); 
	if (source /*&& source != this*/) 
	{  
		const QTreeWidgetItem *item = pMimeData->DragItemData();
		QTreeWidgetItem *pItem = item->clone();
		QTreeWidgetItem *currentItem = this->itemAt(event->pos());
		
		if (currentItem && (currentItem != item))
		{
			currentItem->addChild(pItem);
		} 
		else
		{
			this->addTopLevelItem(pItem);
		}
		if (m_CtrlPressed)
		{
			event->setDropAction(Qt::CopyAction);  
		} 
		else
		{
			event->setDropAction(Qt::MoveAction);  
		}
		//event->setDropAction(Qt::MoveAction);  
		event->accept();  
	} 
}

void MyTreeWidget::performDrag()
{
	QTreeWidgetItem *item = currentItem();  
	if (item) 
	{  

		TreeItemMimeData *mimeData = new TreeItemMimeData;
		mimeData->SetDragData("ItemMimeData",item);

		QDrag *drag = new QDrag(this);  
		drag->setMimeData(mimeData);  
		drag->setPixmap(QPixmap(":/DragDropDemo/Resources/Mail.png"));  
		if (m_CtrlPressed)
		{
			drag->exec(Qt::CopyAction);
		} 
		else
		{
			drag->exec(Qt::MoveAction);
			delete item;
		}
		
	} 
}

以下是我演示的截图