.NET 4 single application instance

Question

I often write .net applications that only support one instance. Formerly I used .net-remoting and now WCF to detect if already an instance of my app is running and giving th

Answer 1

The traditional way to do this is with a mutex, e.g.

bool bNew = true; 
using (Mutex mutex = new Mutex(true, "MYAPP_0D36E4C9-399D-4b05-BDA3-EE059FB77E8D", out bNew))
{
   if (bNew)
   {
       // blah, blah,
       Application.Run(new MainForm());
   }
}

Edit:

I found this code to invoke SetForegroundWindow online, so you can find the other instance of your app and bring it forward:

[DllImport("user32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
static extern bool SetForegroundWindow(IntPtr hWnd);


Process me = Process.GetCurrentProcess();
foreach (Process process in Process.GetProcessesByName (me.ProcessName))
{
   if (process.Id != me.Id)
   {
      SetForegroundWindow (process.MainWindowHandle);
      break;
   }
}

Note that in modern Windows implementations you can only give the foreground away.

Answer 2

I would suggest Singleton-Pattern. Look at this (example for VB.net!):http://vbnotebookfor.net/2007/09/13/introduction-to-the-singleton-pattern-in-vbnet/

Greetz

Answer 3

I use a Mutex, and FindWindow to do this.

Concerning your comment on another answer:
For information on Local and Global mutexes in Terminal Services, follow this link.

Terminal Services client processes can use object names with a "Global\" or "Local\" prefix to explicitly create an object in the global or session name space.

This is the code I use to activate the window:

[DllImport("user32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
static extern bool IsIconic(IntPtr hWnd);

[DllImport("user32.dll")]
static extern bool ShowWindow(IntPtr hWnd, int nCmdShow);
private const int SH_SHOW = 5;
private const int SH_RESTORE = 9;

[DllImport("user32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
static extern bool SetForegroundWindow(IntPtr hWnd);

public void Activate(IntPtr hwnd)
{
    if (IsIconic(hwnd))
        ShowWindow(hwnd, SH_RESTORE);
    else
        ShowWindow(hwnd, SH_SHOW);

    SetForegroundWindow(hwnd);
}

Answer 4

There's a simpler way - with help of WindowsFormsApplicationBase class from Microsoft.VisualBasic.ApplicationServices:

using System;
using System.Collections.Generic;

public class SingleInstanceApplicationWrapper :
Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase 
{
  public SingleInstanceApplicationWrapper()
  {
    IsSingleInstance = true;
  }

  private MyApp m_app;
  protected override bool OnStartup(Microsoft.VisualBasic.ApplicationServices.StartupEventArgs e)
  {
    // here we create our WPF application
    m_app = new MyApp();
    m_app.Run();
    return false;
  }

  protected override void OnStartupNextInstance(Microsoft.VisualBasic.ApplicationServices.StartupNextInstanceEventArgs e)
  {
    m_app.DispatchCommandLineParams(e.CommandLine);
  }
}

public class MyApp : System.Windows.Application
{
  protected override void OnStartup(System.Windows.StartupEventArgs e)
  {
    base.OnStartup(e);
    DispatchCommandLineParams(e.Args);
  }
  public void DispatchCommandLineParams(IEnumerable<string> cmdParams)
  {
    // process command line parameters
    Console.WriteLine(this.GetHashCode() + " - dispatched");
  }
}
public class Program
{
  [STAThread]
  public static void Main(string[] args)
  {
    var wrapper = new SingleInstanceApplicationWrapper();
    wrapper.Run(args);
  }
}