What is the correct way to create a single-instance WPF application?

Question

Using C# and WPF under .NET (rather than Windows Forms or console), what is the correct way to create an application that can only be run as a single instance?

I kno

Answer 1

[I have provided sample code for console and wpf applications below.]

You only have to check the value of the createdNew variable (example below!), after you create the named Mutex instance.

The boolean createdNew will return false:

if the Mutex instance named "YourApplicationNameHere" was already created on the system somewhere

The boolean createdNew will return true:

if this is the first Mutex named "YourApplicationNameHere" on the system.

---

Console application - Example:

static Mutex m = null;

static void Main(string[] args)
{
    const string mutexName = "YourApplicationNameHere";
    bool createdNew = false;

    try
    {
        // Initializes a new instance of the Mutex class with a Boolean value that indicates 
        // whether the calling thread should have initial ownership of the mutex, a string that is the name of the mutex, 
        // and a Boolean value that, when the method returns, indicates whether the calling thread was granted initial ownership of the mutex.

        using (m = new Mutex(true, mutexName, out createdNew))
        {
            if (!createdNew)
            {
                Console.WriteLine("instance is alreday running... shutting down !!!");
                Console.Read();
                return; // Exit the application
            }

            // Run your windows forms app here
            Console.WriteLine("Single instance app is running!");
            Console.ReadLine();
        }


    }
    catch (Exception ex)
    {

        Console.WriteLine(ex.Message);
        Console.ReadLine();
    }
}

WPF-Example:

public partial class App : Application
{
static Mutex m = null;

protected override void OnStartup(StartupEventArgs e)
{

    const string mutexName = "YourApplicationNameHere";
    bool createdNew = false;

    try
    {
        // Initializes a new instance of the Mutex class with a Boolean value that indicates 
        // whether the calling thread should have initial ownership of the mutex, a string that is the name of the mutex, 
        // and a Boolean value that, when the method returns, indicates whether the calling thread was granted initial ownership of the mutex.

        m = new Mutex(true, mutexName, out createdNew);

        if (!createdNew)
        {
            Current.Shutdown(); // Exit the application
        }

    }
    catch (Exception)
    {
        throw;
    }

    base.OnStartup(e);
}


protected override void OnExit(ExitEventArgs e)
{
    if (m != null)
    {
        m.Dispose();
    }
    base.OnExit(e);
}
}