BUG: No WM_MOUSEWHEEL Message is Received after Adding a UserControl to a Form

ID: Q231465

The information in this article applies to:

Microsoft Visual Basic Learning, Professional, and Enterprise Editions for Windows, versions 5.0, 6.0

SYMPTOMS

After adding a User control to a Form, the Visual Basic design environment (IDE) ignores the WM_MOUSEWHEEL message when you roll the wheel of the mouse. This problem does not occur on Windows NT.

CAUSE

The Visual Basic Design Environment (IDE) is not compatible with early versions of the Microsoft Intellimouse driver.

RESOLUTION

Download the latest driver update for the Microsoft Intellimouse from:

http://www.microsoft.com/products/hardware/mouse/driver/default.htm

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article.

MORE INFORMATION

Steps to Reproduce Behavior

WARNING: Failure to unhook a window before its imminent destruction may result in application errors, Invalid Page Faults, and data loss. This is due the fact that the new WindowProc function being pointed to no longer exists, but the window has not been notified of the change. Always unhook the sub-classed window upon unloading the sub-classed form or exiting the application. This is especially important while debugging an application that uses this technique within the Microsoft Visual Basic Development Environment (IDE). Pressing the End button or selecting End from the Run menu without unhooking may cause an Invalid Page Fault and close Microsoft Visual Basic. Changes to the active project will be lost.

Start a new Visual Basic Standard EXE project. Form1 is created by default.

Add the following code to the General Declaration section of Form1:


Option Explicit

Private Sub Form_Load()
   Me.Show
   Call SubClassHookForm
End Sub

Private Sub Form_Unload(Cancel As Integer)
   Call SubClassUnHookForm
End Sub

On the Project menu, select the Add Module menu option.

Add the following code to the General Declaration section of Module1:


Option Explicit

Private MSWHEEL_ROLLMSG     As Long
Private m_PrevWndProc       As Long
Private Const GWL_WNDPROC = (-4)

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 RegisterWindowMessage Lib "user32" _
   Alias "RegisterWindowMessageA" (ByVal lpString As String) As Long

Public Sub SubClassHookForm()
   MSWHEEL_ROLLMSG = RegisterWindowMessage("MSWHEEL_ROLLMSG")
   ' On Windows NT 4.0 and Windows 98, change the above line to
   ' MSWHEEL_ROLLMSG = &H20A
   m_PrevWndProc = SetWindowLong(Form1.hwnd, GWL_WNDPROC, _
                                 AddressOf WindowProc)
End Sub
Public Sub SubClassUnHookForm()
   Call SetWindowLong(Form1.hwnd, GWL_WNDPROC, m_PrevWndProc)
End Sub

Public Function WindowProc(ByVal hwnd As Long, ByVal msg As Long, _
   ByVal wParam As Long, ByVal lParam As Long) As Long

   If msg = MSWHEEL_ROLLMSG Then
      Debug.Print "Receive MSWHEEL_ROLLMSG"
   End If
   WindowProc = CallWindowProc(m_PrevWndProc, hwnd, msg, wParam, lParam)
End Function

Press the F5 key to run the program and roll the wheel button while the mouse pointer is positioned over Form1.

You will see "Receive MSWHEEL_ROLLMSG" displayed in the Immediate Window.

Stop the program. Do NOT use the END button on the toolbar per the warning note at the beginning of this section.

On the File menu, click Add Project... Select ActiveX Control in the Add Project dialog and click OK. UserControl1 is created by default.

Close the Project2 window and add a UserControl1 to Form1.

Press the F5 key to start the program and roll the wheel button while pointing the mouse on Form1.

The string "Receive MSWHEEL_ROLLMSG" no longer occurs in the Immediate Window.

REFERENCES

For additional information, please click the article number below to view the article in the Microsoft Knowledge Base:

Q168795 HOWTO: Hook Into a Window's Messages using AddressOf

Additional query words: wm_mousewheel user control hook

Keywords : kbMouse kbVBp kbVBp500bug kbVBp600bug kbWndwMsg kbGrpVB kbDSupport
Version : WINDOWS:5.0,6.0
Platform : WINDOWS
Issue type : kbbug