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Q238672: FIX: Mouse Hook Not Called When Used in User Controls

Article: Q238672
Product(s): Microsoft Visual Basic for Windows
Version(s): WINDOWS:6.0
Operating System(s): 
Keyword(s): kbAPI kbCtrlCreate kbHook kbSDKWin32 kbVBp600bug kbWndwMsg kbGrpDSVB kbDSupport kbVS600
Last Modified: 26-JUL-2001

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The information in this article applies to:

- Microsoft Visual Basic Learning Edition for Windows, version 6.0 
- Microsoft Visual Basic Professional Edition for Windows, version 6.0 
- Microsoft Visual Basic Enterprise Edition for Windows, version 6.0 
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SYMPTOMS
========

When you install a mouse hook to catch mouse events in a User Control module in
Visual Basic, and then use the User Control module in a Standard EXE project,
running the project in the IDE does not work the first time, but works as
expected after that. However, running the project as a compiled EXE never works.

CAUSE
=====

The User Control uses a mouse hook internally to display ToolTips. However, the
mouse hook set by Visual Basic 6.0 does not call API CallNextHookEx most of the
time. This results in all other mouse hooks at a later position in the hook
chain not being called.

RESOLUTION
==========

To work around the problem, you need to make sure that your mouse hook has an
earlier position than the mouse hook in Visual Basic. One method to achieve this
is to set your mouse hook after the User Control is loaded.

NOTE: Using hooks is not recommended and must be used with caution.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This bug was corrected in the latest service pack for
Visual Studio 6.0.

For additional information about Visual Studio service packs, click the article
numbers below to view the articles in the Microsoft Knowledge Base:

  Q194022 INFO: Visual Studio 6.0 Service Packs, What, Where, Why

  Q194295 HOWTO: Tell That a Visual Studio Service Pack Is Installed

You can download the latest Visual Studio service pack from the following
Microsoft Web site:

  Visual Studio Product Updates
  (http://msdn.microsoft.com/vstudio/downloads/updates.asp)

MORE INFORMATION
================

Steps to Reproduce Behavior
---------------------------

1. Create a new Standard EXE project with Visual Basic 6.0. Form1 is created by
  default.

2. Under Project, select Add module to add a new standard module and Add User
  Control to add a new user control to the project.

3. Add the following code to the standard module:

  Option Explicit

  Public Declare Function CallNextHookEx Lib "user32" _
     (ByVal hHook As Long, _
     ByVal nCode As Long, _
     ByVal wParam As Long, _
     ByVal lParam As Long) As Long

  Public Declare Function UnhookWindowsHookEx Lib "user32" _
     (ByVal hHook As Long) As Long

  Public Declare Function SetWindowsHookEx Lib "user32" _
     Alias "SetWindowsHookExA" _
     (ByVal idHook As Long, _
     ByVal lpfn As Long, _
     ByVal hmod As Long, _
     ByVal dwThreadId As Long) As Long

  Public Const WH_MOUSE = 7
  Public Const HC_ACTION = 0
  Public Const WM_RBUTTONDOWN = &H204

  Public hHook As Long

  Public Function MouseProc(ByVal nCode As Long, ByVal wParam As Long, _
                                ByVal lParam As Long) As Long
     If nCode >= 0 Then
        If nCode = HC_ACTION And wParam = WM_RBUTTONDOWN Then
           MsgBox "get WM_RBUTTONDOWN "
        End If
     End If
     MouseProc = CallNextHookEx(hHook, nCode, wParam, lParam)
  End Function

4. Put the following code into the code window of the User Control module:

  Option Explicit

  Private Sub UserControl_Initialize()
     hHook = SetWindowsHookEx(WH_MOUSE, _
              AddressOf MouseProc, 0&, App.ThreadID)
  End Sub

  Private Sub UserControl_Terminate()
     Call UnhookWindowsHookEx(hHook)
  End Sub

  Public Sub ResetHook()
     Call UnhookWindowsHookEx(hHook)
     hHook = SetWindowsHookEx(WH_MOUSE, _
             AddressOf MouseProc, 0&, App.ThreadID)
  End Sub

5. Close the user control design window and put UserControl1 on the form.

6. Build the project and run the EXE file generated. Right-click on the form and
  note that nothing happens. Close the form to exit.

  NOTE: If you run the application in the Visual Basic IDE, make sure you do not
  click the Stop button. Always unload the form to exit the application,
  otherwise you will get a General Protection Fault (GPF).

Steps to Fix the Problem
------------------------

1. With the project created above, add the following code to the code window of
  Form1:

  Option Explicit

  Private Sub Form_Load()
     UserControl11.ResetHook
  End Sub

2. Recompile the project and run the EXE again. This time, whenever you
  right-click on the form, you get a pop-up message box.

REFERENCES
==========

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

  Q179398 HOWTO: Subclass a UserControl

Additional query words: sp4

======================================================================
Keywords          : kbAPI kbCtrlCreate kbHook kbSDKWin32 kbVBp600bug kbWndwMsg kbGrpDSVB kbDSupport kbVS600sp4fix kbVS600sp5fix 
Technology        : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB600Search kbVB600
Version           : WINDOWS:6.0
Issue type        : kbbug
Solution Type     : kbfix

=============================================================================

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