Binaryworld - How to Subclass a Form ... [ VB -> Subclass ]

'==============inside a MODULE
Option Explicit
'************************************************************
'API
'************************************************************

Private Declare Function CallWindowProc Lib "user32.dll" 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.dll" Alias "SetWindowLongA" ( _
  ByVal hWnd As Long, _
  ByVal nIndex As Long, _
  ByVal dwNewLong As Long) As Long

'************************************************************
'Constants
'************************************************************

Private Const GWL_WNDPROC = -4
Private Const WM_MOUSEMOVE = &H200

'************************************************************
'Variables
'************************************************************

Private hControl As Long
Private lPrevWndProc As Long

Module

Click here to copy the following block

'*************************************************************
'WindowProc
'*************************************************************
Private Function WindowProc(ByVal lWnd As Long, ByVal lMsg As Long, _
  ByVal wParam As Long, ByVal lParam As Long) As Long
  'Selects which messages you want to detect
  Select Case lMsg
    'Example:
    Case WM_MOUSEMOVE
      Form1.Label1.Caption = "MouseMove(" & lMsg & ") Buttons=" & wParam & _
      " Y=" & (lParam Mod 65536) & " X=" & (lParam \ 65535)
  End Select
  'Sends message to previous procedure
  'This is VERY IMPORTANT!!!
  WindowProc = CallWindowProc(lPrevWndProc, lWnd, lMsg, wParam, lParam)
End Function

'*************************************************************
'Hook
'*************************************************************
Public Sub Hook(ByVal hControl_ As Long)
  hControl = hControl_
  lPrevWndProc = SetWindowLong(hControl, GWL_WNDPROC, AddressOf WindowProc)
End Sub

'*************************************************************
'Unhook
'*************************************************************
Public Sub Unhook()
  Call SetWindowLong(hControl, GWL_WNDPROC, lPrevWndProc)
End Sub

Usage

Click here to copy the following block

'Create a Form with a label
Option Explicit

'===========inside a form
'*************************
'USAGE
'*************************

Private Sub Form_Load()
Hook Form1.hWnd
End Sub

Private Sub Form_Unload(Cancel As Integer)
Unhook
End Sub