Microsoft KB Archive/238672

Knowledge Base

FIX: Mouse Hook Not Called When Used in User Controls

Article ID: 238672

Article Last Modified on 8/7/2007

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APPLIES TO

• Microsoft Visual Basic 6.0 Learning Edition
• Microsoft Visual Basic 6.0 Professional Edition
• Microsoft Visual Basic 6.0 Enterprise Edition

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This article was previously published under Q238672

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 that this is a bug in the Microsoft products that are 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 following article numbers to view the articles in the Microsoft Knowledge Base:

194022 INFO: Visual Studio 6.0 Service Packs, What, Where, Why

194295 HOWTO: Tell That a Visual Studio Service Pack Is Installed

To download the latest Visual Studio service pack, visit the following Microsoft Web site:

http://msdn2.microsoft.com/en-us/vstudio/Aa718353.aspx

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:

179398 HOWTO: Subclass a UserControl

Additional query words: sp4

Keywords: kbapi kbbug kbctrlcreate kbfix kbhook kbvs600sp4fix kbvs600sp5fix KB238672

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