让对话框对UPDATE_COMMAND_UI生效

问题：一般情况下我们用UPDATE_COMMAND_UI来修改菜单的状态(enable/disable, check/uncheck, change text)，但这个方法在一个基于对话框上的菜单却没有效果。

void CTestDlg::OnUpdateFileExit(CCmdUI* pCmdUI)

{

     pCmdUI->Enable(FALSE);

     pCmdUI->SetCheck(TRUE);

     pCmdUI->SetRadio(TRUE);

     pCmdUI->SetText("Close");

//以上方法在MDI、SDI程序中都能起作用，在对话框中却没有效果,根本没有调用这个函数。

}

 

原因分析：当显示一个下拉的菜单的时候，在显示菜单前会发送WM_INITMENUPOPUP消息。而CFrameWnd::OnInitMenuPopup函数会刷新这个菜单项，同时如果有UPDATE_COMMAND_UI响应函数，则调用它。通过它来更新反应每个菜单的外观效果(enabled/disabled, checked/unchecked).

在一个基于对话框的程序中，因为没有OnInitMenuPopup函数，所以不会调用UPDATE_COMMAND_UI响应函数，而是使用了CWnd类的默认处理, 这种处理没有调用UPDATE_COMMAND_UI响应函数。

解决方法如下：

第一步：

在对话框类的.cpp文件，添加一个ON_WM_INITMENUPOPUP入口到消息映射里面

BEGIN_MESSAGE_MAP(CTestDlg, CDialog)

//}}AFX_MSG_MAP

ON_WM_INITMENUPOPUP()

END_MESSAGE_MAP()

第二步：

在对话框类的.h文件添加消息函数声明。

// Generated message map functions

//{{AFX_MSG(CDisableDlgMenuDlg)

afx_msg void OnInitMenuPopup(CMenu *pPopupMenu, UINT nIndex,BOOL bSysMenu);

//}}AFX_MSG

DECLARE_MESSAGE_MAP()

第三步：

在对话框类的.cpp文件添加如下函数代码(大部分代码取自WinFrm.cpp文件的函数CFrameWnd::OnInitMenuPopup):

void C******Dlg::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;

   }

}

更详细的信息可参考
http://support.microsoft.com/default.aspx?scid=kb;en-us;242577