How to make sure that there is one instance of the application is running

Question

I want to check when the user double click on applictaion icon that no another instance of this application is already running.

I read about My.Application but i still don't know what to do.

Answer 1

This is something I've used... (C# on .NET 2.0)

    [STAThread]
    private static void Main(string[] args)
    {
        //this follows best practices on
        //ensuring that this is a single instance app.
        string mutexName = "e50cf829-f6b9-471e-8d9f-67eac3699f09";
        bool grantedOwnership;
        //we prefix the mutexName with "Local\\" to allow this to run under terminal services.
        //The "Local\\" prefix forces this into local user space.
        //If we want to forbid this in TS, use the "Global\\" prefix.
        Mutex singleInstanceMutex = new Mutex(true, "Global\\" + mutexName, out grantedOwnership);
        try
        {
            if (!grantedOwnership)
            {
                MessageBox.Show("Error: X is already running.\n\nYou can only run one copy of X at a time.", "X", MessageBoxButtons.OK, MessageBoxIcon.Error, MessageBoxDefaultButton.Button1);
                Application.Exit();
            }
            else
            {
                Application.Run(new X(args));
            }
        }
        finally
        {
            singleInstanceMutex.Close();
        }
    }