Run Only One Copy Of Application

Yet another way to this is as follows:

using System;
using System.Collections.Generic;
using System.Windows.Forms;
using System.Threading;
namespace OnlyOneInstance
{
    static class Program
    {
       
        [STAThread]
        static void Main()
        {
            bool instantiated;
          /* If instantiated is true, this is the first instance of the application; else, another instance is running. */
            Mutex mutex = new Mutex(true, "UniqueID", out instantiated);
            if (!instantiated)
            {
                MessageBox.Show("Already Running");
               return;
            }
            Application.Run(new Form1());
            GC.KeepAlive(mutex);
        }
    }
}

Take a look there[^] to read the complete article.

To download the sample code, you can go here[^]
After downloading, go to bin directory and then debug OnlyOneInstance.exe file twice, you will see a message box which states Program Already Running.