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SingleInstanceApp

The SingleInstanceApp class provides a convenient way to create a single instance application. When your app is launched, it will only allow one instance to run at a time. If another instance of the app is launched, the app will redirect to the already running instance.

1. Disable auto-generated Program code

We need to check for redirection as early as possible, before creating any windows. To do this, we must define the symbol DISABLE_XAML_GENERATED_MAIN in the project file.

Add the following XML to the project file:

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<PropertyGroup>
  <DefineConstants>$(DefineConstants);DISABLE_XAML_GENERATED_MAIN</DefineConstants>
</PropertyGroup>

Adding the DISABLE_XAML_GENERATED_MAIN symbol will disable the auto-generated Program code for your project.

2. Define a Program class with a Main method

Simple

A customized Program.cs file which inherited from SingleInstanceApp must be created, and call the Run method in your Main function.

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public class Program : SingleInstanceApp
{
    [STAThread]
    static int Main(string[] args)
    {
        return Run(args, "MySingleInstanceApp", () => new Program(), () => new App());
    }

    protected override void OnActivated(object sender, AppActivationArguments args)
    {
        ExtendedActivationKind kind = args.Kind;
        Debug.WriteLine("Activated");
    }
}

More Control

If you want more control over how the app is launched and you don’t want to pass the new App() directly, you can use an overload of the Run method that does not require you to pass the new App() instance at the Main method. Instead, you need to override the OnLaunched method in your class.

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public class Program : SingleInstanceApp
{
    [STAThread]
    static int Main(string[] args)
    {
        return Run(args, "MySingleInstanceApp", () => new Program());
    }

    protected override void OnLaunched()
    {
        Application.Start(p =>
        {
            var context = new DispatcherQueueSynchronizationContext(DispatcherQueue.GetForCurrentThread());
            SynchronizationContext.SetSynchronizationContext(context);
            _ = new App();
        });
    }

    protected override void OnActivated(object sender, AppActivationArguments args)
    {
        ExtendedActivationKind kind = args.Kind;
        Debug.WriteLine("Activated");
    }
}

Demo

you can run demo and see this feature.

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