BUG: CWindow::GetTopLevelWindow() returns NULL

• Microsoft Active Template Library, version 2.1

SYMPTOMS

A call to CWindow::GetTopLevelWindow() always returns NULL.

CAUSE

This is due to a bug in the function.

RESOLUTION

Change the function in AtlWin.cpp from:

   HWND CWindow::GetTopLevelWindow() const
   {
      ...
      while(hWndTmp != NULL)
      {
         hWndTmp = (::GetWindowLong(hWndParent, GWL_STYLE) & WS_CHILD) ?
            ::GetParent(hWndParent) :
            ::GetWindow(hWndParent, GW_OWNER);

         hWndParent = hWndTmp;
      }

      return hWndParent;
   }

   HWND CWindow::GetTopLevelWindow() const
   {
      ...
      while(hWndTmp != NULL)
      {
         // Modification
         hWndParent = hWndTmp;

         hWndTmp = (::GetWindowLong(hWndParent, GWL_STYLE) & WS_CHILD) ?
            ::GetParent(hWndParent) :
            ::GetWindow(hWndParent, GW_OWNER);

      }

      return hWndParent;
   }

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. We are researching this bug and will post new information here in the Microsoft Knowledge Base as it becomes available.

(c) Microsoft Corporation 1997, All Rights Reserved. Contributions by Sridhar Madhugiri, Microsoft Corporation