Make only one instance of an application run with VB.NET

by Irina Medvinskaya | Oct 26, 2006 4:29:00 PM

Tags: Microsoft development tools, Programming languages, Irina Medvinskaya, Microsoft Visual Basic.Net, strModName, strProcName, appProc, Visual Basic Tips Newsletter

Takeaway: Irina Medvinskaya presents a way to allow only one instance of an application run with VB.NET. She presents a code example that uses the System.Diagnostics.Process class to determine whether there is more than one instance of an application running.

It's usually a good practice to make sure that only one instance of your application can be run at a time. In order to determine if there are other instances of an application running, you need to get a list of all the processes running and see if an instance of the application is there. In Listing A, I utilize the System.Diagnostics.Process class for this purpose.

In the example, I define an array, appProc, as a Process. Then I define two string variables: strModName and strProcName. The value of variable strModName is set to the Process.GetCurrentProcess.MainModule.ModuleName property, and the value of variable strProcName is set to the System.IO.Path.GetFileNameWithoutExtension, to which I pass the name of the module in strModName. I set the value of the array appProc to the value of Process.GetProcessesByName and pass the strProcName to it. Then, I simply check the Length property of the array appProc. If the length is more than one, it means that there is more then one instance of the application running, which is what I use to base the displayed message box on.

Notes about the example

You should use the example as a part of the Main routine of an application. If you determine that there are other instances of this application running, you can decide on the appropriate action; in most cases, alerting a user to the fact that the application is already running will be enough. If there are no other instances of the application running, you can proceed with the necessary application logic.

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Print/View all Posts Comments on this article

Where is the code djj55 | 10/27/06

VS2005 does this automagically Justin James | 10/27/06

Not available in console program jleather | 10/27/06

Good Point/More Suggestions Justin James | 10/27/06

Making the running instance active BF.NET | 10/27/06

Try this . . . jleather | 10/30/06

Code sample is listed Andy M | 10/27/06

Thanks djj55 | 10/27/06

Here's how to do it in VB6 ChuckSomerville | 10/27/06

RE: Not Vista Compatable? wcarlson@... | 03/04/08

ANSWERED wcarlson@... | 03/11/08