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'==============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

'*************************************************************
'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

'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