callback functions


New member
Feb 3, 2005
Programming Experience

I am new to windows programming. I am trying to capture a WM_USER message in a VB.Net Windows application. This is what I am doing in my class:

DeclareFunction SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal hwnd AsLong, ByVal nIndex AsLong, ByVal dwNewLong AsLong) AsLong
PublicConst GWL_WNDPROC = -4
PublicShared lpPrevWndProc AsLong
Public gHW AsLong

In my Form_Load procedure I am calling SetWindowLong as follows:
lpPrevWndProc = SetWindowLong(gHW, GWL_WNDPROC, AddressOf WindowProc)

I am getting the following error:

"AddressOf expression cannot be converted to Long datatype."

If I replace the argument dwNewLong with a delegate type (the same as the callback function) then I do not get the compile error but the WindowProc function (the callback) does not get called.

Can anyone please help me? I have been working on this for days now.

Thanks much in advance.

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