void CTestDlg::OnUpdateFileExit(CCmdUI* pCmdUI { pCmdUI-> Enable(FALSE); //没有显示为禁用. pCmdUI-> SetCheck(TRUE); // 没有文字前显示选定标记. pCmdUI-> SetRadio(TRUE); // 没有在文字前显示点. pCmdUI-> SetText( "Close "); //没有更改菜单文字. }
原因
在下拉菜单显示的时候, WM_INITMENUPOPUP消息被先发送以显示菜单项。MFC CFrameWnd::OnInitMenuPopup 函数遍历菜单项并为每个菜单项调用更新命令处理函数（如果有的话）.菜单的外观被更新以反映它的状态（启用/禁用,选择/取消选择） 更新用户界面机制在基于对话框的应用程序中不能工作，因为CDialog没有OnInitMenuPopup 处理函数，而使用CWnd 's 默认处理函数,该函数没有为菜单项调用更新命令处理函数。解决 适用下列步骤解决此问题
在消息映射中添加ON_WM_INITMENUPOPUP 项:
BEGIN_MESSAGE_MAP(CTestDlg, CDialog) //{ {AFX_MSG_MAP(CTestDlg) ........................ ........................ //}}AFX_MSG_MAP ON_WM_INITMENUPOPUP() END_MESSAGE_MAP()
在你的对话框类中添加OnInitMenuPopup成员函数且复制下列代码到该函数（注意：代码基本上是从CFrameWnd::OnInitMenuPopup（在WinFrm.cpp中)复制过来的）:
void CTestDlg::OnInitMenuPopup(CMenu *pPopupMenu, UINT nIndex,BOOL bSysMenu) { ASSERT(pPopupMenu != NULL); // Check the enabled state of various menu items. CCmdUI state; state.m_pMenu = pPopupMenu; ASSERT(state.m_pOther == NULL); ASSERT(state.m_pParentMenu == NULL); // Determine if menu is popup in top-level menu and set m_pOther to // it if so (m_pParentMenu == NULL indicates that it is secondary popup). HMENU hParentMenu; if (AfxGetThreadState()-> m_hTrackingMenu == pPopupMenu-> m_hMenu) state.m_pParentMenu = pPopupMenu; // Parent == child for tracking popup. else if ((hParentMenu = ::GetMenu(m_hWnd)) != NULL) { CWnd* pParent = this; // Child windows don 't have menus--need to go to the top! if (pParent != NULL && (hParentMenu = ::GetMenu(pParent-> m_hWnd)) != NULL) { int nIndexMax = ::GetMenuItemCount(hParentMenu); for (int nIndex = 0; nIndex < nIndexMax; nIndex++) { if (::GetSubMenu(hParentMenu, nIndex) == pPopupMenu-> m_hMenu) { // When popup is found, m_pParentMenu is containing menu. state.m_pParentMenu = CMenu::FromHandle(hParentMenu); break; } } } } state.m_nIndexMax = pPopupMenu-> GetMenuItemCount(); for (state.m_nIndex = 0; state.m_nIndex < state.m_nIndexMax; state.m_nIndex++) { state.m_nID = pPopupMenu-> GetMenuItemID(state.m_nIndex); if (state.m_nID == 0) continue; // Menu separator or invalid cmd - ignore it. ASSERT(state.m_pOther == NULL); ASSERT(state.m_pMenu != NULL); if (state.m_nID == (UINT)-1) { // Possibly a popup menu, route to first item of that popup. state.m_pSubMenu = pPopupMenu-> GetSubMenu(state.m_nIndex); if (state.m_pSubMenu == NULL || (state.m_nID = state.m_pSubMenu-> GetMenuItemID(0)) == 0 || state.m_nID == (UINT)-1) { continue; // First item of popup can 't be routed to. } state.DoUpdate(this, TRUE); // Popups are never auto disabled. } else { // Normal menu item. // Auto enable/disable if frame window has m_bAutoMenuEnable // set and command is _not_ a system command. state.m_pSubMenu = NULL; state.DoUpdate(this, FALSE); } // Adjust for menu deletions and additions. UINT nCount = pPopupMenu-> GetMenuItemCount(); if (nCount < state.m_nIndexMax) { state.m_nIndex -= (state.m_nIndexMax - nCount); while (state.m_nIndex < nCount && pPopupMenu-> GetMenuItemID(state.m_nIndex) == state.m_nID) { state.m_nIndex++; } } state.m_nIndexMax = nCount; } } 状态
设计使然。
更多信息
命令用户界面处理函数也被CWnd::OnCommand 调用以确认命令在传递之前没有被禁用。这就是禁用的菜单项的命令处理没有被调用的原因(虽然没有以灰色显示（不可用）)。在这种情况下，菜单项没有被重画以反映菜单项的状态.这是Wincore.cpp 文件中的相关代码:
//在传递命令之前，确定命令没有被禁用 CTestCmdUI state; state.m_nID = nID; OnCmdMsg(nID, CN_UPDATE_COMMAND_UI, &state, NULL); if (!state.m_bEnabled) { TRACE1( "Warning: not executing disabled command %d\n ", nID); return TRUE; } 重现此行为的步骤
使用应用程序向导建立一个基于对话框的应用程序建立一个新的菜单资源，并且向其上添加文件和文件/退出菜单项。 在对话框的属性中设置对话框的菜单为上述菜单. 使用类向导为文件/退出菜单项添加一个UPDATE_COMMAND_UI处理并添加下列语句之一到处理函数。 pCmdUI-> Enable(FALSE); //没有显示为禁用. pCmdUI-> SetCheck(TRUE); // 没有文字前显示选定标记. pCmdUI-> SetRadio(TRUE); // 没有在文字前显示点. pCmdUI-> SetText( "Close "); //没有更改菜单文字. 编译运行此程序。