Prevent an Application starting more than once

[CSD]

Is there a way to prevent a user from starting the same application more than once?

[Jason Isom]

I found this code.

Process ThisProcess = Process.GetCurrentProcess();
Process[] AllProcesses = Process.GetProcessesByName(ThisProcess.ProcessName);
if (AllProcesses.Length > 1)
{
    MessageBox.Show(ThisProcess.ProcessName + " is already running",
        ThisProcess.ProcessName,
        MessageBoxButtons.OK,
        MessageBoxIcon.Error);
}
else
{
    Application.EnableVisualStyles();
    Application.Run(new Form1()); 
}

You can put this in your Main method and it should work.

[Sahir]

On startup you can use the FindWindow API call to check if any windows with same name are active.

[CSD]

Jason, Do I place this code in the Load Event of the form?

Sahir, is there some sample code for the FindWindow way?

[jhammer]

put this code in the main function:

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);
     }
}

Make sure not to forget putting your application name instead of "YourAppName" above (in the mutex decleration).

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<prevAppInstance.GetLength(0) ; i++)
      {
              if(prevAppInstance[i].Id != currentProcess.Id)
              {
                      prevAppInstance[i].Kill();
               }
      }

      // run the aplication
      Application.Run(new Form1());
}

[CSD]

jhammer,

Thanks for that. Which one do you prefer to use? The first one or the second one?

[Sahir]

Sahir, is there some sample code for the FindWindow way?

Yes you probably can find plenty of examples in MSDN and here on Codeguru as well, but I think Jason's suggestion is a better one. Do let us know if it works.

[jhammer]

Which one do you prefer to use? The first one or the second one?

Well, that depends on your needs. If you want to run an application and than prevent running it again, then the first one will do.
If you want to kill the current instance running, and run it all over again, then go for the second one.

[CSD]

jhammer,

I have implemeted your first option and it works very well. It is exactly what I needed.

Cheers.