Single Instance Application in C#

This tutorial will show you how to make your windows forms application only one instance at run-time in C#.NET.

To make restrict the application to just one instance, you should get all actives process, then check your application name with the active process as the following code

public bool IsSingleInstance()
{
     foreach (Process proc in Process.GetProcesses())
     {
          if (proc.MainWindowTitle == this.Text)
               return false;
     }
     return true;
}

You can see your process name in task manager

Don't forget to add a namespace to System.Diagnostics

using System.Diagnostics;

Open your program class, then check your instance as shown below

static class Program
{
    /// <summary>
    /// The main entry point for the application.
    /// </summary>
    [STAThread]
    static void Main()
    {
        if(IsSingleInstance())
           return;
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        Application.Run(new frmMain());
    }
}

Each time you open the application, we will check your application is running