Drag and Drop Enhancement - Auto expand while hovering


I used the code from CodeGuru to implement the Drag and Drop processing in my tree control. I wanted to modify this slightly so that a node would automaticall expand when I dragged a node over a drop target and hovered over it. This is similar to what occurs in Windows Explorer.

The following code snippet could be used in conjunction with the Drag and Drop code offered previously in CodeGuru.

The first step is to add two new variables to your class definition, a Hover Timer Id, and a Hover Point. The Timer Id identifies the timer that is started when you are dragging a tree node and you hover over a drop node for a certain period of time. The Hover Point stores the current point of the hover. This value needs to be stored as it is not available in the OnTimer event handler.

Two events must be defined, if not defined already. They are OnTimer and OnMouseMove. I used the Class Wizard to create them. The following code chunk is from the header file for the tree control. The only items that I included are those that need to be added.


class CMyTree : public CTreeCtrl
{
		.
		. // Definition
		.
private:
	UINT			m_nHoverTimerID;
	POINT			m_HoverPoint;
		.
		.	// Other definition
		.
protected:
	// Generated message map function
	//{{AFX_MSG(CMyTree
	afx_msg void OnTimer(UINT nIDEvent);
	afx_msg void OnMouseMove(UINT nFlags, CPoint point);
	//}}AFX_MS
	DECLARE_MESSAGE_MAP()
}


In the .cpp file, code needs to be added to two functions: OnMouseMove and OnTimer. In OnMouseMove, the hover timer is constantly checked for existence, and if it exists, it is deleted. You only want the OnTimer event called when the mouse pointer is still for a certain period of time. The SetTimer will create a timer, and after the expiration of the selected time period, will send a message triggering the OnTimer event. In the OnTimer event handler, it is a simple matter to kill the timer, get the item currently being hovered over, and issuing an expand node command.

BEGIN_MESSAGE_MAP(CMyTree, CTreeCtrl)
	//{{AFX_MSG_MAP(CMyTree
	ON_WM_TIMER()
	ON_WM_MOUSEMOVE()
	//}}AFX_MSG_MA
	END_MESSAGE_MAP()

void CMyTree::OnMouseMove(UINT nFlags, CPoint point) 
{
	HTREEITEM		hitem;
	UINT			flags;

	if ( m_nHoverTimerID )
	{
		KillTimer( m_nHoverTimerID );
		m_nHoverTimerID = 0;
	}

	if (m_bDragging)
	{
		ASSERT(m_pImageList != NULL);
		m_pImageList->DragMove(point);

		m_nHoverTimerID = SetTimer(2, 750, NULL);
		m_HoverPoint = point;

		if ((hitem = HitTest(point, &flags)) != NULL)
		{
			m_pImageList->DragLeave(this);
			SelectDropTarget(hitem);
			m_hitemDrop = hitem;
			m_pImageList->DragEnter(this, point);
		}

		m_pImageList->DragShowNolock(TRUE);
	}
	
	CTreeCtrl::OnMouseMove(nFlags, point);
}

void CMyTree::OnTimer(UINT nIDEvent) 
{
	if ( nIDEvent == m_nHoverTimerID )
	{
		KillTimer( m_nHoverTimerID );
		m_nHoverTimerID = 0;

		HTREEITEM	trItem	= 0;
		uint		uFlag	= 0;

		trItem = HitTest(m_HoverPoint, &uFlag);

		if ( trItem )
		{
			SelectItem( trItem );
			Expand(trItem,TVE_EXPAND);	
		}
	}
	else
	{
		CTreeCtrl::OnTimer(nIDEvent);
	}
}



Comments

  • Fixing bug: cluttering after expanding

    Posted by Legacy on 05/10/2003 12:00am

    Originally posted by: Pika


    At first, thank you Pete for your code! Very useful!

    I've noticed that after tree item is expanded (under the mouse pointer) the tree control moves the piece of screen down (to free space to show child items). And my dragged image is moved there also!! :( and it stays there until the tree is updated somehow.
    So, my solution was to refresh tree control on expanding. Here it is:


    void CMyTree::OnTimer(UINT nIDEvent)
    {
    ...
    trItem = HitTest(m_HoverPoint, &uFlag);

    if ( trItem )
    {
    //ADDED!!!:
    // hide the dragged image
    CImageList::DragShowNolock(FALSE);

    SelectItem( trItem );
    Expand(trItem,TVE_EXPAND);

    //ADDED!!:
    // update the tree control
    InvalidateRect(NULL);
    UpdateWindow();
    // show dragged image back
    CImageList::DragShowNolock(TRUE);

    }
    ...
    }

    Reply
Leave a Comment
  • Your email address will not be published. All fields are required.

Top White Papers and Webcasts

  • Data integrity and ultra-high performance dictate the success and growth of many companies. One of these companies is BridgePay Network Solutions, a recently launched and rapidly growing financial services organization that allows merchants around the world to process millions of daily credit card transactions. Due to the nature of their business, their IT team needed to strike the perfect balance between meeting regulatory-mandated data security measures with the lowest possible levels of latency and …

  • Intelligent N+X Redundancy, Placement Affinities, & Future Proofing in the Virtualized Data Center Virtualization brought about the ability to simplify business continuity management in IT. Workload portability and data replication capabilities mean that physical infrastructure failures no longer need impact application services, and they can rapidly be recovered even in the event of complete site failure. However, Enterprises and Service Providers face new challenges ensuring they have enough compute …

Most Popular Programming Stories

More for Developers

RSS Feeds

Thanks for your registration, follow us on our social networks to keep up-to-date