Window Hooking Questions

Question

Is am using this:

SetWindowsHookEx(WH_CALLWNDPROC, ...);

I can see the messages I want to process, but I want to prevent those message from reaching the target window. So I tried this:

SetWindowsHookEx(WH_GETMESSAGE, ...);

When I do this I can modify the message, and prevent the target window from processing it, but this hook doesn't see the messages I need to process. I presume this is because it is being posted to the target window's queue, not sent? Is there a way around this issue? I have heard that window sub-classing might be able to accomplish this, but can I subclass a window in a different process? Is there a way to do this using hooks?

Answer 1

You can't subclass a window in a another process, but the hook DLL should be able to subclass the window you're interested in. WH_GETMESSAGE and WH_CALLWNDPROC hooks run in the context of the process receiving the message, so at that point you have an "in" to subclass the target's window.

Answer 2

You could try subclassing the target window and then filter the messages.

Answer 3

The hook documentation suggests this can't be done but I assume this strategy might work: use SetWindowsHookEx(WH_CALLWNDPROC, ... )

In the procedure just modify the message you want to throw away to an unused WM_ value.

LRESULT CALLBACK CallWndProc(int nCode,WPARAM wParam,LPARAM lParam)
{
   CWPSTRUCT *C=(CWPSTRUCT *)lParam;

   if ( ...we are interested in this one) {
     ..deal with this message here...
     //Modify the message so that the client will ignore it
     C->message=WM_USER+44; //presumably ignored by client
   }       
   return GetNextHook(...);
}

Nasty but easy?