Preventing Multiple Instances of a VB.NET Application

[mpappert]

Hey Everyone!

 

I want to prevent users from creating multiple instances of my application, instead have it set focus to the original instance (in VB6 you could use the App.PrevInstance method, as shown in the the MS article below).

 

MS Knowledge Base Article :: Q185730

 

Is there a .NET equivilent?

 

 

Thanks!

M.

[Volte]

I found this in the MSDN.

' 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

[mpappert]

Great! Thanks .. I did search the Microsoft Site, but I didn't come up with anything (just the VB6 one I posted above) .. Is there a way to have it set the focus to the already existing instance?

 

M.

[Derek Stone]

I'm not aware of any method of setting focus to other windows outside your application without using the Win32 API.

[Robby]

This returns the correct string as expected..

Diagnostics.Process.GetCurrentProcess.ProcessName

but the rest does not.

[Volte]

You can get the handle of the application's main window by using

the .MainWindowHandle property of the process you found.

I don't know, but I assume the first one started will be 0 in the

array of returned processes.

[Robby]

I think you may need to write to the Eventlog for this to work.

[mpappert]

The following code will recognize when a multiple instance of an application has been run:

 

' Prevent Multiple Instances of the Application
Dim appProcesses As Process() = _
  Process.GetProcessesByName(Diagnostics.Process.GetCurrentProcess.ProcessName)

If appProcesses.Length > 1 Then
  ' Terminate This Instance
End If

This code is placed on the main form and after MyBase.New() and before the InitializeComponent() ...

 

However, this leads to my next question ... I can't terminate the instance with a simple Me.Close() :confused: It just continues to execute, the code works because I've put a message box with the info in it and it works ... Is there another way I can terminate this instance?

 

Thanks!

M.

[Derek Stone]

Application.Exit()

[mpappert]

That's a new command I didn't know Derek, but still doesn't work .. here is the code that I have on my form ... I tried moving the "IF ... THEN" after the SplashScreen.Dispose() but that didn't work either (I thought maybe it would have to go after the initialization was done) .. the msgbox appears so I know it's being raised, but can't kill the darn app! Am I going to have to code it into the FormLoad event?

 

Thanks again! :-\

M.

 

 

Public Sub New()
  MyBase.New()

  '[MP]   Prevent Multiple Instances of the Application
  Dim appProcesses As Process() = _
     Process.GetProcessesByName(Diagnostics.Process.GetCurrentProcess.ProcessName)

  If appProcesses.Length > 1 Then
     MsgBox("Application.Exit Triggered")
     Application.Exit()
  End If

  '[MP]   Show Splash screen while the Application Loads
  Dim SplashScreen As New frmSplashScreen()
  SplashScreen.ShowDialog()
  SplashScreen.Update()

  '[MP]   Initialize the Application (Global Settings)
  Initialize(Me)

  'This call is required by the Windows Form Designer.
  InitializeComponent()

  'Add any initialization after the InitializeComponent() call
   SplashScreen.Dispose()

   End Sub

[Robby]

I'm curious, is the

MsgBox("Application.Exit Triggered")

even triggering?

[mpappert]

Yes, which is what is strange .. I get the msgbox which indicates that it's a second instance and should close .. yet, both Me.Close() and Application.Exit() both don't kill the app .. it runs as normal!?!

 

Very strange ..

 

M.

[Volte]

You could make a Sub Main to initialize your program with. For

example, set your startup object to Sub Main from the project

properties, and add this class:

Public Class Init
   Public Shared Sub Main()
       If findPreviousInstance() Then
           Application.Exit()
       Else
           Dim frm As New Form1()

           Application.Run(frm)
       End If
   End Sub

   Public Shared Function findPreviousInstance() As Boolean
       'do your check
   End Function
End Class

[mpappert]

It Works!!!! Thanks everyone for your help!

 

M. :D

[Robby]

I still can't get this to work... the value of appProcesses is always 0

Public Sub New()
  MyBase.New()

  Dim appProcesses As Process() = Process.GetProcessesByName(Diagnostics.Process.GetCurrentProcess.ProcessName)

  If appProcesses.Length > 1 Then
     MsgBox("Triggered")
  End If
  InitializeComponent()
End Sub

[mpappert]

Hey Robby,

 

Create a class module named "Initialize" and replace all code with the following:

 

Option Explicit On 


Public Class Initialize

  Shared Sub Main()

  '[MP]   Prevent Multiple Instances of the Application
  Dim appProcesses As Process() = _
  Process.GetProcessesByName(Diagnostics.Process.GetCurrentProcess.ProcessName)
  If appProcesses.Length > 1 Then
     Application.Exit()
  Else
     Dim Main As New frmMain()
     Application.Run(Main)
  End If

End Sub

 

Set your startup project as Sub Main() and replace 'frmMain' with whatever your main form is called.

 

This works .. I'm running it without problems! If you still have problems, then I'll post a sample app and you can try that ...

 

M.