You cannot change the state of a menu item from its command user-interface handler if the menu is attached to a dialog box in Visual C++


Note Microsoft Visual C++ .NET 2002 and Microsoft Visual C++ .NET 2003 support both the managed code model that is provided by the Microsoft .NET Framework and the unmanaged native Microsoft Windows code model. The information in this article applies only to unmanaged Visual C++ code. Microsoft Visual C++ 2005 supports both the managed code model that is provided by the Microsoft .NET Framework and the unmanaged native Microsoft Windows code model.

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

    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 the Behavior

Follow these steps to reproduce this behavior in Visual C++ .NET:

  1. Create an MFC 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 the dialog box Properties window. To do this, open the dialog resource in the dialog editor. In the Properties window, click select Menu. The ID of the new menu resource is displayed in the Menu property editor drop-down list.
  4. Add an UPDATE_COMMAND_UI handler for File/Exit menu item. To do this, right-clicking File/Exit in the menu editor, and then click Add Event Handler. In the Event Handler wizard, add the UPDATE_COMMAND_UI handler to the project CDialog derived class. Click Add and Edit to create the handler, and then add one of these statements to the generated handler method:
    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 more information, click the following article number to view the article in the Microsoft Knowledge Base:

141751 Adding control bars to dialog boxes in MFC