application already running?!?!

[BrianHawley]

A neater option if a previous instance of the application is running is just to switch to it:

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
 
Public Sub Main()
 
  If App.PrevInstance Then
    ActivatePrevInstance
  End If
 
  'Etc......
 
End sub
 
Public Sub ActivatePrevInstance()
 
  Dim OldTitle As String, 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 = "Duplicate 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