<snip>

Yup, that's a pretty common scenario. Time to update the FAQ to include
that link, I suspect...

Hi Alex,

Thank you for your reply.

As for the option of using mutex, we could use ChannelServices to register
a channel for the main form when the application is run for the first time.

When the application is run for the second time, we could create a proxy
for the previous instance using RemotingServices. Pass the command line
parameters of the second instance or call a function inside the main form
of the original instance, and then exit the second instance.

The following is a sample. It requires that you add a reference to
System.Runtime.Remoting in your application.

using System.Runtime.Remoting;
using System.Runtime.Remoting.Channels;
using System.Runtime.Remoting.Channels.Tcp;
using System.Threading;

static class Program
{
       [STAThread]
       static void Main(string[] args)
       {          
           bool firstInstance = false;
           string safeName = Application.UserAppDataPath.Replace(@"\",
"_");
           Mutex mutex = new Mutex(true, safeName, out firstInstance);
           if(!firstInstance)
           {
               string formUrl = "tcp://localhost:1313/form1";
               Form1 otherMainfrm =
(Form1)RemotingServices.Connect(typeof(Form1), formUrl);
               otherMainfrm.Method1(args);
               return;
           }
           ChannelServices.RegisterChannel(new TcpChannel(1313),false);
           RemotingServices.Marshal(form1, "form1");
           Application.Run(form1);
       }

       static Form1 form1 = new Form1();        
}

public partial class Form1 : Form
   {
       public Form1()
       {
           InitializeComponent();
       }
       delegate void MethodCallback(string[] args);

       public void Method1(string[] args)
       {
           // Note that it is not allowed for non-UI thread to access
controls on the form, instead, we should use the Invoke method of the form
to execute a delegate on the UI thread that own's the control's underlying
windows handle.
           if(this.InvokeRequired)
           {
               MethodCallback callback = new MethodCallback(Method1);
               this.Invoke(callback, new object[] { args });
               return;
           }
           string command = "";
           for(int i =0;i<args.Length; i++)
           {
               command += args[i] + " ";
           }
           this.textBox1.Text = command;
       }
   }

As the option of using WindowsFormsApplicationBase, it's easy and straight
forward to do this. The following is a sample.

using System.Windows.Forms;
using Microsoft.VisualBasic.ApplicationServices;

class Program:WindowsFormsApplicationBase
{      
       [STAThread]
       static void Main(string[] commandline)
       {          
           Program prog = new Program();
           mainform = new Form1();
           prog.MainForm = mainform;
           prog.Run(commandline);
       }
       static Form1 mainform = null;
       public Program()
       {
           this.IsSingleInstance = true;
       }
       protected override void
OnStartupNextInstance(StartupNextInstanceEventArgs eventArgs)
       {
           string command = "";
           for(int i =0 ; i<eventArgs.CommandLine.Count; i++)
           {
               command += eventArgs.CommandLine[i] + " ";
           }
           MessageBox.Show("this is the second instance! " +
eventArgs.CommandLine.Count.ToString() + " " + command);
           
           base.OnStartupNextInstance(eventArgs);
           mainform.Method1();
       }
}

Hope this helps.
If you have any question, please feel free to let me know.

Sincerely,
Linda Liu
Microsoft Online Community Support