INFO: Modifying the System Menu of an MDI Child Window (77930)

MORE INFORMATION

It is common to try to alter a window's system menu during the processing of its WM_CREATE message. This method has no effect on the system menu of an MDI child, however, because of the way a MDI child window is created:

1. The MDI client window calls the CreateWindowEx() function to create the window.
2. Then, the MDI client window replaces the default system menu with the special MDI child system menu.

The WM_CREATE message is sent to the child window by CreateWindowEx(). Changes to the MDI child's system menu on WM_CREATE have no effect because the MDI client assigns a special MDI system menu to the child after CreateWindowEx() returns.

To work around this design decision, the child window procedure can post a custom message to itself during the processing of its WM_CREATE message. This custom message is processed after the MDI client has finished creating the MDI child. The code for this workaround might resemble the following:

   #define WM_ADDMENUITEM (WM_USER+1)

   LONG FAR PASCAL MDIChildWndProc(HWND hWnd,

                                   WORD wMsg,
                                   WORD wParam,
                                   LONG lParam)

   {

       switch (wMsg)
          {
       case WM_CREATE:
          PostMessage(hWnd, WM_ADDMENUITEM, 0, 0L);
          break;

       case WM_ADDMENUITEM:
          {
          HMENU        hMenu;

          hMenu = GetSystemMenu(hWnd, FALSE);
          InsertMenu(hMenu, -1, MF_BYPOSITION, IDM_NEW,
                (LPSTR)"New Item\0");
          DrawMenuBar(hWnd);
          }
          break;

       default:
          return DefMDIChildProc(hWnd, wMsg, wParam, lParam);
          }

       return 0;

   }