FIX: Timer Callbacks Not Called in MFC 4.2 Applications (154652)

CAUSE

MFC 4.2 added the capability to add message map entries for messages that are posted to the queue but are not destined for any particular window (for example, messages posted with PostThreadMessage).

This can be done using the ON_THREAD_MESSAGE macro. To enable this capability, a change was made in CWinThread::PreTranslateMessage that prevents any message that does not have an HWND from being routed through the message pump. Consequently, messages that do not have an HWND are not passed to the Win32 DispatchMessage API call.

Timer callback functions are invoked through a posted WM_TIMER message. The WM_TIMER message has NULL as the hwnd member and the lParam points to the callback function. The callback function is invoked by Windows when a WM_TIMER message with a NULL hwnd is passed to DispatchMessage.

Because MFC 4.2 does not pass these messages to DispatchMessage, the timer callback function will not be called.

   BOOL CMyApp::PreTranslateMessage( MSG *pMsg )
   {
       // If this is a timer callback message let it pass on through to the
       // DispatchMessage call.
       if( (pMsg->message==WM_TIMER) && (pMsg->hwnd==NULL) )
           return FALSE;
       ...
       // The rest of your PreTranslateMessage goes here.
       ...

       return CWinApp::PreTranslateMessage(pMsg);
   }