by Anonymous (267 Submissions)
Category: Windows System Services
Compatability: Visual Basic 5.0
Difficulty: Unknown Difficulty
Originally Published: Wed 22nd December 1999
Date Added: Mon 8th February 2021
Rating: 
(1 Votes)
Correct way to 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
VBcoders
'Store handle to this form's window
gHW = Me.hWnd
'Call procedure to begin capturing messages for this window
Hook
End Sub
'in VB6 on this can be placed in Form_Terminate
Private Sub Form_Unload(Cancel As Integer)
'Call procedure to stop intercepting the messages for this window
Unhook
End Sub
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
Function WindowProc(ByVal hw As Long, ByVal uMsg As Long, _
ByVal wParam As Long, ByVal lParam As Long) As Long
'Check for the ActivateApp message
If uMsg = WM_ACTIVATEAPP Then
'Check to see if Activating the application
If wParam <> 0 Then
'Application Received Focus
Form1.Caption = "Focus Restored"
Else
'Application Lost Focus
Form1.Caption = "Focus Lost"
End If
End If
'Pass message on to the original window message handler
WindowProc = CallWindowProc(lpPrevWndProc, hw, uMsg, wParam, _
lParam)
End Function
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