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Determine when your visual basic application gains or loses focus.

Determine when your visual basic application gains or loses focus.

API Declarations



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

Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" _
(ByVal hwnd As Long, ByVal nIndex As Long, _
ByVal dwNewLong As Long) As Long

Public Const WM_ACTIVATEAPP = &H1C
Public Const GWL_WNDPROC = -4

Global lpPrevWndProc As Long
Global gHW As Long



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Sub Form_Load()
   'Store handle to this form's window
   gHW = Me.hWnd

   'Call procedure to begin capturing messages for this window
   Hook
End Sub

Private Sub Form_Unload(Cancel As Integer)
   'Call procedure to stop intercepting the messages for this window
   Unhook
End Sub

'******************************************************************
'Paste the following code into the main module:
Public Sub Hook()
   'Establish a hook to capture messages to this window
   lpPrevWndProc = SetWindowLong(gHW, GWL_WNDPROC, _
     AddressOf WindowProc)
End Sub

Public Sub Unhook()
   Dim temp As Long

   'Reset the message handler for this window
   temp = SetWindowLong(gHW, GWL_WNDPROC, lpPrevWndProc)
End Sub