Single Instance of WPF Application

gistfile1.txt

First you can start by removing the StartupUri attribute from the App.Xaml file so that it looks like this...

<Application x:Class="SingleInstance.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
</Application>

After that, you can go to the App.xaml.cs file and change it so it looks like this...

public partial class App 
{
    // give the mutex a  unique name
    private const string MutexName = "##||ThisApp||##";
    // declare the mutex
    private readonly Mutex _mutex;
    // overload the constructor
    bool createdNew;
    public App() 
    {
        // overloaded mutex constructor which outs a boolean
        // telling if the mutex is new or not.
        // see http://msdn.microsoft.com/en-us/library/System.Threading.Mutex.aspx
        _mutex = new Mutex(true, MutexName, out createdNew);
        if (!createdNew)
        {
            // if the mutex already exists, notify and quit
            MessageBox.Show("This program is already running");
            Application.Current.Shutdown(0);
        }
    }
    protected override void OnStartup(StartupEventArgs e)
    {
        if (!createdNew) return;
        // overload the OnStartup so that the main window 
        // is constructed and visible
        MainWindow mw = new MainWindow();
        mw.Show();
    }
}