PRB: Update Command UI Handlers Do Not Work for Menu Attached to a Dialog Box

• Microsoft Visual C++, 32-bit Editions, version 6.0, used with:
  • The Microsoft Foundation Classes (MFC)

SYMPTOMS

Changing the state (enable/disable, check/uncheck, change text) of a menu item from its command user-interface (UI) handler does not work correctly if the menu is attached to a dialog box:

void CTestDlg::OnUpdateFileExit(CCmdUI* pCmdUI) 
{
    pCmdUI->Enable(FALSE); //Not calling the command handler, but does not show as disabled.
    pCmdUI->SetCheck(TRUE); // Does not show check mark before the text.
    pCmdUI->SetRadio(TRUE); // Does not show dot before the text.
    pCmdUI->SetText("Close"); //Does not change the text.
} 

CAUSE

When a drop-down menu is displayed, the WM_INITMENUPOPUP message is sent prior to displaying the menu items. The MFC CFrameWnd::OnInitMenuPopup function iterates through the menu items and calls the update command UI handler for the item, if there is one. The appearance of each menu item is updated to reflect its state (enabled/disabled, checked/unchecked).

The update UI mechanism doesn't work for a dialog box-based application because CDialog has no OnInitMenuPopup handler and it uses CWnd's default handler, which does not call update command UI handlers for menu items.

RESOLUTION

Use the following steps to resolve this problem:

1. Add an ON_WM_INITMENUPOPUP entry to the message map:

   
   BEGIN_MESSAGE_MAP(CTestDlg, CDialog)
   	//{{AFX_MSG_MAP(CTestDlg)
                           ........................
                           ........................
   	//}}AFX_MSG_MAP
   
   	ON_WM_INITMENUPOPUP()
   END_MESSAGE_MAP() 




2. Add a OnInitMenuPopup member function to your dialog box class and copy the following code (note that this code is taken largely from CFrameWnd::OnInitMenuPopup in WinFrm.cpp):

   
   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;
       }
   } 

STATUS

This behavior is by design.

MORE INFORMATION

The update command UI handler is also called from CWnd::OnCommand to make sure that command has not become disabled before routing. This is why the command handler is not called for a disabled menu item even though it is not grayed (unavailable). Menu items are not drawn to reflect their status in this case. This is the related code from the Wincore.cpp file:

   // Make sure command has not become disabled before routing.	
   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;
   } 

Steps to Reproduce Behavior

1. Create a dialog-based application by using AppWizard.



2. Create a new menu resource and add the File and File/Exit menu items to it.



3. Set this menu as the menu for the dialog box in properties.



4. Add an UPDATE_COMMAND_UI handler for File/Exit menu item by using ClassWizard, and then add either one of the statements to the handler.
   

   
   	pCmdUI->Enable(FALSE); //Not calling the handler, but does not show as disabled
   	pCmdUI->SetCheck(TRUE); // Does not show check mark before the text.
   	pCmdUI->SetRadio(TRUE); // Does not show dot before the text.
   	pCmdUI->SetText("Close"); //Does not change the text. 




5. Build and run the application.

REFERENCES

For additional information, click the article number below to view the article in the Microsoft Knowledge Base:

Q141751 SAMPLE: Adding Control Bars to Dialog Boxes in MFC

© Microsoft Corporation 9/29/1999, All Rights Reserved.
Contributions by Sreedhar Pelluru, Microsoft Corporation

Additional query words: WM_INITMENUPOPUP ON_UPDATE_COMMAND_UI

Keywords : kbDlg kbMenu kbMFC KbUIDesign kbVC600 kbDSupport kbGrpMFCATL
Version : winnt:6.0
Platform : winnt
Issue type : kbprb