What does "_instance = this;" mean? [closed]

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I am taking over a c# windows project. In the startup object app(), there is _instance = this;. What does it mean? Is it just for a instance and can be used by other method like shutdown etc? Is this something to force singleton? If yes, how does it force to only have one instance?

_instance is defined as below:

private static App _instance;

Source codes are here:

public partial class App : Application
{
    private static App _instance;

    private SplashView _splashView;

    public App()
    {
        if (!NetworkConnectivityManager.CheckConnectivity())
        {
            Shutdown();
            return;
        }

        try
        {
            try
            {
                AppServiceManager.Start();
            }
            catch
            {
                Retryer.DoWithRetries(delegate()
                {
                    ActivateOtherInstance();
                    Shutdown();
                    return;
                }, 4, 1000);
            }

            ShowSplashScreen();
            ShutdownMode = ShutdownMode.OnExplicitShutdown;
            _instance = this;
            ExceptionManager.SubscribeToUnhandledAppDomainException();
        }
        catch (Exception ex)
        {
            ExceptionManager.HandleException(ex);
        }
    }

    public static void ShutdownApp()
    {
        _instance.Shutdown();
    }

Please let me know if they are enough to tell. Thanks a lot.

---

If you ask about how to make a class singleton in C#

class A
{
   private static readonly A _instance = new A();
   public virtual A instance 
   { 
        get
        {
             return _instance;
        }
   }
   private A()
   {
   }
}

That is a typical way to make singleton in C#.

For your code, it depends how to use it. For singleton, it doesn't make any sense.

Ok, I read your code.

It is simply a bad design. It is used for calling shutdown without have the pointer to a instance of the class.

If you happened to new this class somewhere else, calling App.Shutdown won't shutdown all the App.

If you only create one App class, rewrite it with a proper singleton. If you have multiple App instance running at the same time, rewrite it with a proper instance manager.

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Without other logic in the class somewhere, that kind of variable declaration is redundant and unnecessary, since any other method, like shutdown, can reference this just as easily.