PRB: Accelerator Key Not Disabled with ON_UPDATE_COMMAND_UI

The information in this article applies to:

• The Microsoft Foundation Classes (MFC) included with: Microsoft Visual C++ for Windows, version 1.5, 1.51, and 1.52

SYMPTOMS

If a popup menu contains a submenu and a menu item on that submenu uses an accelerator key, you can't enable or disable the accelerator key by calling CCmdUI::Enable() in the ON_UPDATE_COMMAND_UI for that menu item.

Example

For example, if an application has the following menu structure for the main application window, pressing CTRL+M sends the command for MenuItem.

   File  Other
          Popup
             MenuItem Ctrl+M
          Item Ctrl+T

   void CMyView::OnUpdateMenuItem(CCmdUI* pCmdUI)
      {
         pCmdUI->Enable(m_bEnabled);
      }

CAUSE

The ON_UPDATE_COMMAND_UI() handler is called for menu items from the OnInitMenuPopup() handler of the menu's frame window. Windows only sends the WM_INITMENUPOPUP message to top-level popups, not submenus, when an accelerator key is used. This explains why the accelerator key for Item in the menu above will be disabled as expected but not the menu item in the submenu.

RESOLUTION

To resolve the problem:

• Use a flag in your menu item handler to see whether this menu item should be enabled or not. If it shouldn't be enabled, return immediately from the function without processing the command. You will still want to use an ON_UPDATE_COMMAND_UI() handler for disabling (greying out) the menu item.
• Disable the menu item explicitly by using the EnableMenuItem() function. Continue to use the ON_UPDATE_COMMAND_UI() handler as well.