How-to prevent an Application from running more than once.

How-to prevent an Application from running more than once.

In VS.NET 2003 I often need an application to run as Singleton, meaning - run only once. This is a typical behavior of servers. Unfortunately, there is no support for this in Framework 1.1 .

So here is an elegant solution. The code is in C#, but may be applied to VB.NET as well.

The Code - Option 1
This will prevent an application from running more than once:
--------------------------------------------

using System.Threading;
using System.Runtime.InteropServices;
public class Form1 : Form
{
(...)
   [STAThread]
   static void Main()
   {
      bool createdNew;
      Mutex m = new Mutex(true, "YourAppName", out createdNew);
      if (! createdNew)
      {
         // app is already running...
         MessageBox.Show("Only one instance of this application is allowed at a time.");
         return;
      }
      Application.Run(new Form1());
      // keep the mutex reference alive until the normal termination of the program
      GC.KeepAlive(m);
   }
}

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This code is added to the Main method (In VB.NET you will need to create one, click here to see how).
Notice: Make sure that you set a unique name for the application instead of YourAppName in the mutex decleration in my code (or you will prevent other applications from running).

The Code - Option 2
The next section will close the PREVIOUS instance of the application:-------------------------------------------------

using System;
using System.ComponentModel;
using System.Diagnostics;

(...)
static void Main()
{
   // get the name of the current process
   Process currentProcess = Process.GetCurrentProcess();
   string currProcessName = currentProcess.ProcessName;
   // get all instances of the this application
   Process[] prevAppInstance = Process.GetProcessesByName(currProcessName);
   // kill all other instances of this application
   for(int i = 0 ; i {
      if(prevAppInstance[i].Id != currentProcess.Id)
      {
         prevAppInstance[i].Kill();
      }
   }
   // run the aplication
   Application.Run(new Form1());
}

-------------------------
In this case you will close the instance that is running and keep the new one running (sometimes this bevior is more appropriate).

For more discussion, click here