Instance of program already running?

[Kurt]

How to find out whether there's already running an instance of your application when a user wants to start it?

I would like to allow only one instance running on a machine.

[divil]

Straight from the help:

 

In Visual Basic 6.0, the PrevInstance property of the App object was used to determine if a previous instance of an application was running. There is no equivalent for this property in Visual Basic .NET; however, the following code can be used to test for a previous instance:

 

' Visual Basic .NET
Function PrevInstance() As Boolean
  If Ubound(Diagnostics.Process.GetProcessesByName(Diagnostics.Process.GetCurrentProcess.ProcessName)) > 0 Then
     Return True
  Else
     Return False
  End If
End Function

[Kurt]

thanx divil. Any suggestions where the best placement would be to call this check (in the constructor of the start up form or something?), so I can cancel the start up of a second instance?

[divil]

Make yourself a Sub Main to start the application, then only do your Application.Run(new form1()) if the check succeeds.

[Winston]

thats wat i used although it works fine

but theres a work around which is renaming the exe

[quwiltw]

Check out [msdn]System.Threading.Mutex[/msdn]. Which will allow you to do something like this, which prevents any renaming workarounds.

      Dim objLock As New System.Threading.Mutex(False, "MyAppLock")
       Dim blnIsRunning As Boolean = Not mtxLock.WaitOne(0, False)