如何使用MFC禁用和灰显顶级菜单项

 ```c++

 CMenu* pMenu = AfxGetMainWnd()->GetMenu();

 CMenu* pSubMenu = pMenu->GetSubMenu(0); // 0表示要灰显的菜单项所在的顶级菜单

 pSubMenu->EnableMenuItem(ID_MENU_ITEM, MF_BYCOMMAND | MF_GRAYED); // ID_MENU_ITEM是要灰显的菜单项的ID

 ```