Application instance

[T Cordon]

How to determine if another instance of the application is running so that
ir doesn't run multiple instances?


Thanks

 

[Greg Burns]

Option Strict On
Imports System.Threading

Module Main
Private Sub SubMain()

SingletonApp.Run(New MyForm)

End Sub
Enc Module


Public Class SingletonApp

Shared m_Mutex As Mutex
Public Shared Sub Run(ByVal mainForm As Form)
If (IsFirstInstance()) Then
AddHandler Application.ApplicationExit, AddressOf OnExit
Application.Run(mainForm)
End If
End Sub
Public Shared Function IsFirstInstance() As Boolean

' use this to create a unique guid for your app, or Tools->Create
GUID...
'Dim g As New Guid
'g = Guid.NewGuid
'Debug.WriteLine(g.ToString)

m_Mutex = New Mutex(False, "8ca35a66-6e9a-41d4-a87d-d9755b1f88c4") '
arbitrary GUID
Dim owned As Boolean = False
owned = m_Mutex.WaitOne(TimeSpan.Zero, False)
Return owned
End Function

Public Shared Sub OnExit(ByVal sender As Object, ByVal args As
EventArgs)
m_Mutex.ReleaseMutex()
m_Mutex.Close()
End Sub
End Class

 

[Klaus H. Probst]

The only sure way is to create a Mutex and try to acquire ownership of it
every time your app opens.

Luckily using a mutex from .NET is simple.

 

[Ken Tucker [MVP]]

Hi,

Start your app from sub main use a mutex to see if there is another
instance running.

Public Sub main()

Dim owned As Boolean

Dim mut As New System.Threading.Mutex(True, "xvcjsdf67AS124#$3", owned)

If owned Then

Application.Run(New Form1)

mut.ReleaseMutex()

Else

MessageBox.Show("A previous instance is already running")

End If

End Sub



Ken

 

[Herfried K. Wagner [MVP]]

How to determine if another instance of the application is running so that
ir doesn't run multiple instances?

<URL:http://www.pobox.com/~skeet/csharp/faq/#one.application.instance>

 

[Bob Powell [MVP]]

Windows forms Tips and Tricks has an example that also brings the running
instance to the foreground.

http://www.bobpowell.net/tipstricks.htm

--
Bob Powell [MVP]
Visual C#, System.Drawing

The Image Transition Library wraps up and LED style instrumentation is
available in the June of Well Formed for C# or VB programmers
http://www.bobpowell.net/currentissue.htm

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Bob's Blog: http://bobpowelldotnet.blogspot.com/atom.xml

 

[Guest]

Having detected another instance of the application is it possible to make that instance become the active application instead of
MessageBox.Show("A previous instance is already running")

Thanks

 

[The Grim Reaper]

Um.... I might be missing something blindling obvious here... but when I
upgraded some VB6 code the other day, it changed my code to this;

Public Sub Main()
Try
' Disallow other copies running
If GetProcessesByName(GetCurrentProcess.ProcessName).GetUpperBound(0)
= 0 Then
Application.EnableVisualStyles()
Application.Run(New frmMain)
End If
Catch vException As Exception
MessageBox.Show(vException.Message, "Error", MessageBoxButtons.OK,
MessageBoxIcon.Error)
End Try
End Sub

I take it this code neglects to let your application run if another process
with the same name also happens to be running... I suppose if your app is
called MyDatabaseAppOnMyPC.exe, the chances of a conflict are low.. lol
_______________________
The Grim Reaper

 

[Greg Burns]

Curious. What did the VB 6 code look like before the upgrade?

Yes, simply checking for the same named process is not very full proof. I
am surprised the upgrade wizard would go that route. A mutex seems to be the
safer bet.

Greg

 

[The Grim Reaper]

Oh yes, I agree the mutex thing looks a whole lot more solid!! The old VB6
code (I've found it in most of my old projects after a brief search - dunno
where I got it from) was something like this;

Sub Form_Load()
If App.PrevInstance Then
Msgbox "<app name> is already running!", vbOKOnly + vbInformation,
"Stupid User Alert"
Unload Me
End If
End Sub

Seems oh-so-simple looking back... lol.
____________________________
The Grim Reaper