Subclassing and Hooking with Visual Basic

Subclassing a Third-PartyActiveX Control

This is the easiest of the four types of subclassing discussed in this chapter. Subclassing a third-party ActiveX control is exactly the same as subclassing a VB form. There is no difference because the system sees both the control and the form as windows. Using SetWindowLongPtr, you would subclass the control just like you would any other window:

Private Sub Form_Load(  )
    gCtrlWndProc = SetWindowLongPtr(Button1.GetHwnd, GWL_WNDPROC, AddressOf CtrlProc)
End Sub

You set up the subclass function just like you would any other subclass function: by passing the window message on to the original window procedure by way of CallWindowProc, as the following subclass function indicates:

Public Function CtrlProc(ByVal hWnd As Long, ByVal uMsg As Long, _
				ByVal wParam As Long, ByVal lParam As Long) As Long
	'Do subclassing work here
    gCtrlWndProc = SetWindowLongPtr(Button1.GetHwnd, GWL_WNDPROC, _
                                    AddressOf CtrlProc)

Using SetWindowLongPtr, the subclass procedure is removed from the control, similar to removing the subclass procedure from any other window:

Private Sub Form_Unload(Cancel As Integer)
    Dim RetVal As Long
    RetVal = SetWindowLongPtr(Button1.GetHwnd, GWL_WNDPROC, gCtrlWndProc)
End Sub

Now that we can subclass a control, we will move on to subclassing a control that we create within the VB environment.