Exetools - How to?-Prevent multiple instance of an application

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How to?-Prevent multiple instance of an application

I am writin the app in vb 6.0 and vb.net and want to know how to prevent the application from being opened multiple times on the same computer.

i.e. If the application is already open clicking on the app's icon will only bring the currently open application to the front instead of opening another instance of the app.

Thank you for all help given.

One of the best and easiest way to prevent ur app. from running again when its run , is to create a named Mutex for ur app. then you should check it at the begining of ur app. and if CreateMutex returns the ERROR_ALREADY_EXISTS , then you can be sure that another instance of ur app is running and do whtevere u want ! (Find more info about the "CreateMutex" API in MSDN) :rolleyes:

I prefer to use FindWindowEx API to find a similar window
You can find your window properties by SPY++

I think that it's more useful because your process may be killed and the user won't be able to launch your app by the reboot.

ba bye

VB.Net

Code:

            '#Zone " Prevent multiple instances "

            If UBound(Diagnostics.Process.GetProcessesByName(Diagnostics.Process.GetCurrentProcess.ProcessName)) > 0 Then

                'Send opening form's TEXT property as a parameter to the function "ActivatePrevInstance"

                Dim PrevHndl As Long

                Dim result As Long

                Dim argStrAppToFind As String = "XXXXXXXXXXXXXXXX"

                'Variable to hold individual Process

                Dim objProcess As New Process

                'Collection of all the Processes running on local machine

                Dim objProcesses() As Process

                ''Get all processes into the collection

                objProcesses = Process.GetProcesses()



                For Each objProcess In objProcesses

                    ''Check and exit if we have SMS running already

                    If objProcess.MainWindowTitle.Length > 9 Or objProcess.MainWindowTitle = "xxxxxxxxxxxxxxxxxxxx" Then



                        If objProcess.MainWindowTitle = "xxxxxxxxxxxxxxxxxxxxxx" Then

                            MsgBox("Another instance of " & argStrAppToFind & " is already running on this machine. You cannot run TWO instances at a time. Please use the other instance.", MsgBoxStyle.Exclamation)

                            PrevHndl = objProcess.MainWindowHandle.ToInt32()

                            Exit For

                        End If

                        If (UCase(objProcess.MainWindowTitle.Substring(0, 12)) = UCase(argStrAppToFind)) Then

                            MsgBox("Another instance of " & argStrAppToFind & " is already running on this machine. You cannot run TWO instances at a time. Please use the other instance.", MsgBoxStyle.Exclamation)

                            PrevHndl = objProcess.MainWindowHandle.ToInt32()

                            Exit For

                        End If



                    End If

                Next

                If PrevHndl = 0 Then Exit Sub 'if No previous instance found exit the application.

                ''If found

                result = OpenIcon(PrevHndl) 'Restore the program.

                result = SetForegroundWindow(PrevHndl) 'Activate the application.



                End 'End the current instance of the application.

            End If

            '#End Zone

hmm, for vb6 it can be done very simply using "App.PrevInstance".

Code:

Private Form_Load( )

     If App.PrevInstance Then

          Unload Me

     End If

End Sub

for vb.net it's a bit different, but this function should work

Code:

Function PrevInstance() As Boolean

If Ubound(Diagnostics.Process.GetProcessesByName(Diagnostics.Process.GetCurrentProcess).ProcessName)) > 0 Then

     Return True 

Else 

     Return False  

End If

End Function

There is also a similar way to do it in vb.net here
http://www.thescarms.com/dotNet/SingleInstance.asp

:D

if you use MUTEXes as suggested by "just4urim", be sure to release your mutex using a call to releaseMutex() before your program quits

Great! Thank you for all the help. I will report back once ive tested it

in addition, you'll need to find the previously running app (findwindow), and make it the active window before you exit your program (use win messages). this way, running a 2nd instance of your app brings up the first instance.