How To Display Descriptions of Menu Items When Highlighted

MORE INFORMATION

The following steps demonstrate how to create a sample application that provides descriptions for menu items when the menu items are highlighted. To achieve this functionality, you must use a concept known as subclassing to allow you to detect when the WM_MENUSELECT message occurs. This message occurs whenever a menu selection is either highlighted or not highlighted.

For more information on subclassing, please see the following article in the Microsoft Knowledge Base: NOTE: Failure to unhook a window before its destruction results in application errors, Invalid Page Faults, or data loss. This occurs because the new WindowProc function that is being pointed to no longer exists, but the window has not been notified of the change. Always unhook the subclassed window upon unloading the subclassed form or exiting the application.

This is especially important when you use Visual Basic to debug an application that includes subclassing. Pressing the End button or selecting End from the Run menu without unhooking causes an Invalid Page Fault and closes Microsoft Visual Basic.

Steps to Create Sample Application

1. Create a new Standard EXE project.
2. Create the following menu on Form1 using the Menu Editor:

   Menu Caption        Menu Name
   -----------        ---------
   
   File               mnuFile
     New              mnuNew
     Open             mnuOpen
     Close            mnuClose
   
   Edit               mnuEdit
     Cut              mnuCut
     Copy             mnuCopy
     Paste            mnuPaste
        Normal        mnuPasteNormal
        Special       mnuPasteSpecial
   						

   NOTE: You should create the menu captions exactly as shown. If you choose to add accelerators, you need to modify the following code to reflect these changes to your captions.
3. Paste the following code into the code window for Form1:

   Option Explicit
   
   Private Sub Form_Load()
       'Store a handle to this form.
       gHW = Me.hwnd
   
       'Call this Sub procedure to begin hooking into messages.
       Hook
   End Sub
   
   Private Sub Form_Unload(Cancel As Integer)
       'Call this Sub procedure to cease hooking into messages.
       Unhook
   End Sub
   						

4. Add a standard module to the project.
5. Paste the following code into the module:

   Option Explicit
   
   Private Declare Function CallWindowProc Lib "user32" _
      Alias "CallWindowProcA" (ByVal lpPrevWndFunc As Long, _
      ByVal hwnd As Long, ByVal Msg As Long, _
      ByVal wParam As Long, ByVal lParam As Long) As Long
   
   Private Declare Function SetWindowLong Lib "user32" _
      Alias "SetWindowLongA" (ByVal hwnd As Long, _
      ByVal nIndex As Long, ByVal dwNewLong As Long) As Long
   
   Private Declare Function GetMenu Lib "user32" _
     (ByVal hwnd As Long) As Long
   
   Private Declare Function GetSubMenu Lib "user32" _
     (ByVal hMenu As Long, ByVal nPos As Long) As Long
   
   Private Declare Function GetMenuItemCount Lib "user32" _
     (ByVal hMenu As Long) As Long
   
   Private Declare Function GetMenuState Lib "user32" _
     (ByVal hMenu As Long, ByVal wID As Long, _
      ByVal wFlags As Long) As Long
   
   Private Declare Function GetMenuString Lib "user32" _
      Alias "GetMenuStringA" (ByVal hMenu As Long, _
      ByVal wIDItem As Long, ByVal lpString As String, _
      ByVal nMaxCount As Long, ByVal wFlag As Long) As Long
   
   Private Const MF_BYPOSITION = &H400&
   Private Const MF_HILITE = &H80&
   Private Const WM_MENUSELECT = &H11F
   Private Const GWL_WNDPROC = -4
   
   Public lpPrevWndProc As Long
   Public gHW As Long
   
   Public Sub Hook()
       'Begin hooking into messages.
       lpPrevWndProc = SetWindowLong(gHW, GWL_WNDPROC, _
       AddressOf WindowProc)
   End Sub
   
   Public Sub Unhook()
       'Cease hooking into messages.
       SetWindowLong gHW, GWL_WNDPROC, lpPrevWndProc
   End Sub
   
   Function AnyLit(hSubSubMenu As Long) As Long
       Dim i As Long
       Dim MenuCount As Long
   
       'Get the number of items in the menu.
       MenuCount = GetMenuItemCount(hSubSubMenu)
   
       'Loop through the menu items.
       For i = 0 To MenuCount - 1
           'Check whether this item is highlighted.
           If GetMenuState(hSubSubMenu, i, MF_BYPOSITION) And _
                  MF_HILITE Then
               AnyLit = True
               Exit Function
           End If
       Next i
   
       'Return FALSE, no items highlighted.
       AnyLit = False
   End Function
   
   Private Sub WalkSubMenu(hSubMenu As Long)
       Dim i As Long
       Dim MenuItems As Long
       Dim hSubSubMenu As Long
       Dim buffer As String
       Dim result As Long
   
       'Get the count of menu items in this menu.
       MenuItems = GetMenuItemCount(hSubMenu)
   
       'Loop through all the items on the menu.
       For i = 0 To MenuItems - 1
           'Determine whether this item is highlighted.
           If GetMenuState(hSubMenu, i, MF_BYPOSITION) And _
                  MF_HILITE Then
               'Attempt to get a submenu for each menu item.
               hSubSubMenu = GetSubMenu(hSubMenu, i)
   
               'Check for a submenu with something selected on it.
               If hSubSubMenu And AnyLit(hSubSubMenu) Then
                   'There is a submenu with a selection so walk it.
                   WalkSubMenu hSubSubMenu
               Else    'This is it.
                   'Set buffer size.
                   buffer = Space(255)
   
                   'Call the API to get the caption for the menu item.
                   result = GetMenuString(hSubMenu, i, buffer, _
                      Len(buffer), MF_BYPOSITION)
   
                   'Trim the buffer of extra characters.
                   buffer = Left$(buffer, result)
   
                   'Set the caption of the form to a description of the
                   'menu item.
                   Form1.Caption = GetDescription(buffer)
   
                   'Exit this Sub procedure.
                   Exit Sub
               End If
           End If
       Next i
   End Sub
   
   Public Sub FindHilite(TheForm As Form)
       Dim hMenu As Long
       Dim hSubMenu As Long
       Dim i As Long
       Dim MenuCount As Long
   
       'Clear any previous description.
       Form1.Caption = ""
   
       'Get the menu handle.
       hMenu = GetMenu(TheForm.hwnd)
   
       'Check to see if there is no menu.
       If hMenu <> 0 Then
           'Get the number of top-level menus.
           MenuCount = GetMenuItemCount(hMenu)
   
           'Enumerate through all top-level menus.
           For i = 0 To MenuCount - 1
               'Ignore top-level menus not currently selected.
               If GetMenuState(hMenu, i, MF_BYPOSITION) And _
                      MF_HILITE Then
                   'Get a handle to the submenu.
                   hSubMenu = GetSubMenu(hMenu, i)
   
                   'Walk the submenu.
                   WalkSubMenu hSubMenu
               End If
           Next i
       End If
   End Sub
   
   Private Function GetDescription(MenuCaption As String) As String
       'Determine the description of the menu item.
       Select Case MenuCaption
           Case "New"
               GetDescription = "Creates a new document"
           Case "Open"
               GetDescription = "Opens a Document"
           Case "Close"
               GetDescription = "Closes Document"
           Case "Cut"
               GetDescription = "Cuts Selection to Clipboard"
           Case "Copy"
               GetDescription = "Copies Selection to Clipboard"
           Case "Paste"
               GetDescription = "Pastes Contents of Clipboard"
           Case "Normal"
               GetDescription = "Regular Paste"
           Case "Special"
               GetDescription = "Special Paste"
           Case Else
               GetDescription = ""
       End Select
   End Function
   
   Function WindowProc(ByVal hw As Long, ByVal uMsg As Long, _
          ByVal wParam As Long, ByVal lParam As Long) As Long
   
       'Check for a menu selection message.
       If uMsg = WM_MENUSELECT Then
           FindHilite Form1
       End If
   
       'Pass the message to Windows for processing.
       WindowProc = CallWindowProc(lpPrevWndProc, hw, uMsg, _
          wParam, lParam)
   End Function
   						

6. Click Start or click the F5 key to start the program. Open various menu items and observe the changes that occur to the form's caption.