FIX: UserControls with Menus Cause Resource Leak

Steps to Reproduce and Work Around the Problem

1. Start a new Visual Basic Standard EXE project. Form1 is created by default. The NegotiateMenus property of Form1 is set to True by default.
2. On the Project menu, click Add User Control to add UserControl1 to the project.
3. Add a CommandButton and a CheckBox control to UserControl1.
4. Create a menu with several items and sub items on UserControl1. Set the NegotiatePosition property of each top level menu item to 1-Left.
5. Add the following code to the General Declarations section of UserControl1:

   Option Explicit
   '
   '
   ' Demonstrates how to free menu resources orphaned by a UserControl.
   
   ' Zero-based array and one-based counter
   ' of cached UserControl submenus
   
   Private m_ahMenus() As Long
   Private m_nMenus As Integer
   
   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 IsMenu Lib "user32" (ByVal hMenu As Long) As Long
   Private Declare Function DestroyMenu Lib "user32" (ByVal hMenu As Long) _
      As Long
   
   Private Declare Function GetParent Lib "user32" (ByVal hwnd As Long) As Long
   
   Private Sub UserControl_EnterFocus()
      ' the UserControl's main menu has been created and has
      ' replaced the form's main menu before any control on the
      ' UserControl gains input focus.
   
      If Check1.Value And (m_nMenus = 0) Then
         Call LoadMenus(GetMenu(GetParent(UserControl.hwnd))) ' Form1.hwnd))
         Debug.Print "UserControl submenus loaded: " & m_nMenus
      End If
   End Sub
   
   Private Sub UserControl_ExitFocus()
      ' the UserControl's main menu has been destroyed, and has
      ' replaced been by the form's main menu. *But* all submenus
      ' under UserControl's main menu have not been destroyed.
   
      If m_nMenus Then
         Debug.Print "UserControl submenus destroyed: " & DestroyMenus
      End If
   End Sub
   
   Private Sub UserControl_Initialize()
      Check1.Caption = "Workaround"
      BorderStyle = 1
   End Sub
   
   Private Sub Check1_Click()
      If (Check1.Value = vbChecked) And (m_nMenus = 0) Then
         Call LoadMenus(GetMenu(GetParent(UserControl.hwnd)))
         Debug.Print "UserControl submenus loaded: " & m_nMenus
      ElseIf (Check1.Value = vbUnchecked) And m_nMenus Then
         Erase m_ahMenus ' Clear the module level variables
         m_nMenus = 0
         Debug.Print "No UserControl submenus will be destroyed"
      End If
   End Sub
   
   ' Pass the UserControl's top level menu on first call
   
   Private Sub LoadMenus(hMenu As Long)
      Dim nItems As Integer
      Dim i As Integer
      Dim hSubmenu As Long
      
      nItems = GetMenuItemCount(hMenu)
   
      For i = 0 To nItems - 1
         hSubmenu = GetSubMenu(hMenu, i)
   
         If IsMenu(hSubmenu) Then
            ReDim Preserve m_ahMenus(m_nMenus)
            m_ahMenus(m_nMenus) = hSubmenu
            m_nMenus = m_nMenus + 1
         End If
   
         Call LoadMenus(hSubmenu) ' recurse through sub menu
      Next
   End Sub
   
   Private Function DestroyMenus() As Integer
      Dim i As Integer
      Dim n As Integer
   
      For i = m_nMenus - 1 To 0 Step -1
         If IsMenu(m_ahMenus(i)) Then
            ' Will destroy all submenus under the current submenu, toggle the
            ' For expression comments above to destroy individual submenus.
            Call DestroyMenu(m_ahMenus(i))
            n = n + 1
         End If
      Next
   
     ' Clear the mod level variables
      Erase m_ahMenus
      m_nMenus = 0
   
      DestroyMenus = n
   
   End Function
   					

6. Close all of UserControl1's open windows.
7. Add a CommandButton and a UserControl1 to Form1. UserControl11 is created by default.
8. Add the following code to the General Declarations section of Form1:

   Private Sub Form_Click()
      Dim i As Integer
      For i = 1 To 2000
         UserControl11.SetFocus
         DoEvents ' IMPORTANT:  Allows SetFocus to complete before proceeding
         Command1.SetFocus
         DoEvents
         Me.Caption = i
      Next i
   End Sub
   					

9. Save your project.
10. On Windows 95, Windows 98, or Windows Me, start the Resource Meter. The Windows NT or Windows 2000 Task Manager does not provide the same level of functionality.
11. Run the project, and click on the form. Under Win9x, the Resource Meter shows a steady decline in User and System resources.
12. Click the form again. On most systems, you observe problems with menu-related functionality such as Copy, Paste, and the Start menu. You may also see changes to fonts and icons used by the system.
13. Click the Stop button. You may receive an Out of Memory dialog, which you can dismiss. Terminate the Visual Basic IDE and observe that the resources are released.
14. Restart the Visual Basic IDE. Reload and run your project.
15. Select the checkbox labeled Workaround and click the form. The Resource Meter shows no decline in resources.

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