FIX: Mouse Hook Not Called When Used in User Controls

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).

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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.

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