Preventing inadvertant drag and drop


Have you ever had the experience that you clicked on the Explorer to bring it to the foreground and the directory got moved. This happens if the mouse moves before the mouse button is released. Many of the users of my program had this experience and heres what I did to prevent inadvertant drag - drop. I basically imposed the restriction that after pressing the mouse button the cursor should remain on the item for a few milliseconds before dragging can be initiated.
 

Step 1: Declare member variable

Add a member variable to hold the tick count when the user presses the mouse button.
 
protected:
        DWORD   m_dwDragStart;


Step 2: Define a constant to specify the delay

We define DRAG_DELAY with a value 80. You might want to use a different value.
#define DRAG_DELAY 80


Step 3: Add handler for WM_LBUTTONDOWN

The only interesting thing we do here is initialize the m_dwDragStart variable. GetTickCount() returns the number of milliseconds since Windows was started.
 
void CTreeCtrlX::OnLButtonDown(UINT nFlags, CPoint point) 
{
        m_dwDragStart = GetTickCount();
        CTreeCtrl::OnLButtonDown(nFlags, point);
}


Step 4: Check for sufficient delay in TVN_BEGINDRAG handler

Insert the following code right at the beginning of the TVN_BEGINDRAG handler. In a previous section we have used the name OnBeginDrag() for the handler function. If the delay since the user pressed the left mouse button is not sufficient, we not initiate the drag and drop process.
 
        // This code is to prevent accidental drags.
        if( (GetTickCount() - m_dwDragStart) < DRAG_DELAY )
                return;



Comments

  • Title

    Posted by Legacy on 04/09/2002 12:00am

    Originally posted by: Name

    Comment

    Reply
  • h

    Posted by Legacy on 04/09/2002 12:00am

    Originally posted by: h

    h

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  • Your email address will not be published.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

Top White Papers and Webcasts

  • There is no understating the impact of security and network connectivity on today's cloud environments. Yes, clouds can scale, expedite processing, and reduce costs, but they also incur risks associated with multi-tenancy, availability, and access control. How users connect to the cloud is vital because not only are security risks non-negotiable, but performance, flexibility, and reliability are critical as well, which leads to a heavy emphasis on combining strong security with private network ecosystems. …

  • Are you truly leading your team or simply managing them? Organizations need leaders and your team needs someone to follow. With some ongoing development, you could become that leader. Learn the top leadership qualities that inspire others to want to follow you and the direction of your company.

Most Popular Programming Stories

More for Developers

RSS Feeds

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