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Prevent multiple instances of a 32-bit application.

Prevent multiple instances of a 32-bit application.

API Declarations



Declare Function OpenIcon Lib "user32" (ByVal hwnd As Long) As Long
Declare Function FindWindow Lib "user32" Alias "FindWindowA" _
(ByVal lpClassName As String, ByVal lpWindowName As String) _
As Long
Declare Function GetWindow Lib "user32" _
(ByVal hwnd As Long, ByVal wCmd As Long) As Long
Declare Function SetForegroundWindow Lib "user32" _
(ByVal hwnd As Long) As Long



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   If App.PrevInstance Then
      ActivatePrevInstance
   End If
End Sub

Sub ActivatePrevInstance()
   Dim OldTitle As String
   Dim PrevHndl As Long
   Dim result As Long

   'Save the title of the application.
   OldTitle = App.Title

   'Rename the title of this application so FindWindow
   'will not find this application instance.
   App.Title = "unwanted instance"

   'Attempt to get window handle using VB4 class name.
   PrevHndl = FindWindow("ThunderRTMain", OldTitle)

   'Check for no success.
   If PrevHndl = 0 Then
      'Attempt to get window handle using VB5 class name.
      PrevHndl = FindWindow("ThunderRT5Main", OldTitle)
   End If

   'Check if found
   If PrevHndl = 0 Then
   'Attempt to get window handle using VB6 class name
   PrevHndl = FindWindow("ThunderRT6Main", OldTitle)
   End If

   'Check if found
   If PrevHndl = 0 Then
      'No previous instance found.
      Exit Sub
   End If

   'Get handle to previous window.
   PrevHndl = GetWindow(PrevHndl, GW_HWNDPREV)

   'Restore the program.
   result = OpenIcon(PrevHndl)

   'Activate the application.
   result = SetForegroundWindow(PrevHndl)

   'End the application.
   End
End Sub