PRB: Hidden MDI Child Window Causes Corrupted MDI Window Menu

WINDOWS   | WINDOWS NT

The information in this article applies to:

• The Microsoft Foundation Classes (MFC), included with:

      - Microsoft Visual C++ for Windows, versions 1.0, 1.5
      - Microsoft Visual C++, 32-bit Edition, versions 1.0, 2.0, 2.1,
        2.2, 4.0, 4.1, 4.2
  

SYMPTOMS

If an MDI child window is hidden or disabled, the Window menu is not properly updated for the visible MDI child windows. Specifically, the Window menu will continue to show deleted MDI child windows or will fail to add new MDI child windows to the list.

CAUSE

These problems occur only after at least one MDI child window has been destroyed. When Windows destroys an MDI child window, it moves activation to a different window. This activation change causes MFC to change and refresh the MDI frame window's menu. Windows does not handle this menu refresh message correctly while in the process of destroying an MDI child window when other windows are hidden or disabled. This problem does not occur if the window being destroyed is hidden or disabled.

RESOLUTION

To work around this problem, program your application to ensure that that an MDI child window is always hidden or disabled before it is destroyed. The destruction of MDI child windows is managed by the MDICLIENT window in the processing of the WM_MDIDESTROY message. You can customize the behavior of this message as follows:

1. Subclass the MDICLIENT window and provide a handler for the message. For an example that shows how to subclass the MDICLIENT window, please see the article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q129471

      TITLE     : How to SubClass the MDIClient by Using MFC
   
   

2. Add a message handler for the WM_MDIDESTROY message to the class used to subclass the MDICLIENT window; this example calls it the CMDIClientWnd class. This message is not listed by ClassWizard, so you will need to add the handler manually. If you are unfamiliar with how to do this, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q99848

      TITLE     : INF: Use ON_MESSAGE() Macro to Map Less-Common Messages
   
   

3. Implement the OnMDIDestroy function as follows:

   LRESULT CMDIClientWnd::OnMDIDestroy(WPARAM wParam,LPARAM lParam) {

         // wParam contains the hwnd of the child being destroyed
         HWND hwndChild = (HWND) wParam;
         ::ShowWindow(hwndChild,SW_HIDE);
         return Default();
   

   };