What does "_instance = this;" mean?
<p>I am taking over a c# windows project.  In the startup object app(), there is <code>_instance  = this;</code>.  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?</p>

<p>_instance is defined as below:</p>

<p>private static App _instance;</p>

<p>Source codes are here:</p>

<pre><code>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();
    }
</code></pre>

<p>Please let me know if they are enough to tell.  Thanks a lot.</p>
