Difference between revisions of "Dragging windows"

Revision as of 12:37, 9 April 2006

So, you want to drag a window without using the real title bar?

I have seen lots of people using their own code in the mouse move event to do this, and I've even done it myself.

Until I found the following code:

Declare Function ReleaseCapture Lib "user32" () As Long
Declare Function SendMessage Lib "user32" Alias "SendMessageA" _
  (ByVal hWnd As Long, ByVal wMsg As Long, ByVal wParam As Long, _
  lParam As Any) As Long

Const WM_NCLBUTTONDOWN = &HA1
Const HTCAPTION = 2

And when you want to do the dragging itself:

ReleaseCapture
SendMessage Form.hWnd, WM_NCLBUTTONDOWN, HTCAPTION, ByVal 0&

This should go in the mousedown event of the control/object you want to drag the window by.

It has various advantages over home grown code:

1. It's faster and rarely suffers from flickering.
2. It's easier. Two lines once compared to a huge routine (or two?)
3. It obeys the windows rules and settings on drawing windows while moving.

If you want to use this to drag a control, just replace Form.hWnd with Control.hWnd. This will NOT work with windowless controls like Labels or ImageBoxes.

See also

• Earlsoft ReleaseCapture API page