HOWTO: How to Use TrackPopupMenu() and Update UI Handlers

MORE INFORMATION

Menu items in an MFC application are updated in response to the WM_INITMENUPOPUP message. The MFC CFrameWnd::OnInitMenuPopup() function has special code for handling the Update UI mechanism.

The code in CFrameWnd::OnInitMenuPopup iterates through the menu items and checks for the Update UI and Command handlers in the command route, for each item. Depending on the result of this search, it updates the state of the menu item.

The WM_INITMENUPOPUP message is sent only to the owner of the menu. Hence for the menus to be updated correctly, you need to make a CFrameWnd-derived class the owner of the floating popup menu.

The Update UI mechanism doesn't work for a dialog-based application because the code that calls the UI handlers is not found in a CDialog-derived class.

The following sample code displays the File popup menu in the CView-derived class (CMyView) in response to the WM_RBUTTONUP message. Note that the main frame window pointer is used in the call to the CMenu::TrackPopupMenu() function, so the Update UI mechanism will work correctly.

Sample Code

void CMyView::OnRButtonUp(UINT nFlags, CPoint point)
    {
    // Calling the base class function.
    CView::OnRButtonUp(nFlags, point);

    // Get the top level menu from the main application window.
    CWnd*  pMainWindow = AfxGetMainWnd();
    CMenu* pTopLevelMenu = pMainWindow->GetMenu();

    // Get the File popup menu from the top level menu.
    CMenu *pFileMenu = pTopLevelMenu->GetSubMenu(0);

    // Convert the mouse location to screen coordinates before passing
    // it to the TrackPopupMenu() function.
    ClientToScreen(&point);

    // Display the File popup menu as a floating popup menu in the
    // client area of the main application window.
    pFileMenu->TrackPopupMenu(TPM_LEFTALIGN | TPM_LEFTBUTTON,
        point.x,
        point.y,
        pMainWindow);    // owner is the main application window
    }