Shutting down a WPF application from App.xaml.cs

Question

I am currently writing a WPF application which does command-line argument handling in App.xaml.cs (which is necessary because the Startup event seems to be the recommended way of getting at those arguments). Based on the arguments I want to exit the program at that point already which, as far as I know, should be done in WPF with Application.Current.Shutdown() or in this case (as I am in the current application object) probably also just this.Shutdown().

The only problem is that this doesn't seem to work right. I've stepped through with the debugger and code after the Shutdown() line still gets executed which leads to errors afterwards in the method, since I expected the application not to live that long. Also the main window (declared in the StartupUri attribute in XAML) still gets loaded.

I've checked the documentation of that method and found nothing in the remarks that tell me that I shouldn't use it during Application.Startup or Application at all.

So, what is the right way to exit the program at that point, i. e. the Startup event handler in an Application object?

Phooey

What are the errors you're getting? Please update your question. – Rounding

Click Here for a simple and working answer – Herbartian

Answer 1

First remove the StartupUri property from App.xaml and then use the following:

    protected override void OnStartup(StartupEventArgs e)
    {
        base.OnStartup(e);

        bool doShutDown = ...;

        if (doShutDown)
        {
            Shutdown(1);
            return;
        }
        else
        {
            this.StartupUri = new Uri("Window1.xaml", UriKind.Relative);
        }
    }

Pryor

Still doesn't work right :( Specifically I'm getting NullReferenceExceptions in the main window's constructor, which may be easily circumvented. But as far as I understand it shutting down the application should work without instantiating the window referenced by StartupUri. – Phooey

I changed my answer to show you how you can avoid your main window to be created. It is important that you first remove the StartupUri from App.xaml. – Pryor

Thanks. It works now. But I find it kinda unintuitive that the StartupUri is always loaded regardless whether the application should already have exited. – Phooey

This doesn't work if you are trying to shut down from InitApplication(), as in my case. Even if StartupUri is null, which it already is in my case because I have no main window, this.Shutdown() has no effect. – Overshoe

InitApplication() is executed before OnStartup(), so I have to set a boolean during InitApplication(), then call return, and check for the boolean in OnStartup() and then exit as above. – Overshoe

When I do this, the program exits but the console window doesn't redraw the console. weird. – Dissolution

Answer 2

If you remove the StartupUri from app.xaml for an application with a MainWindow you need to make sure you make the following call in your OnStartup method otherwise the application will not terminate when your MainWindow closes.

this.ShutdownMode = System.Windows.ShutdownMode.OnMainWindowClose;

@Frank Schwieterman, something along these lines may help you with your console window issue.

Coltun

This page details the WPF startup and shutdown procedures very clearly... blackwasp.co.uk/WPFStartupShutdown.aspx – Letha

Answer 3

I did this a little differently to avoid having to set the StartupUri and ShutdownMode properties. First edit the App.xaml file and replace StartupUri with Startup:

<Application x:Class="Menu.App"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:local="clr-namespace:Menu"
         Startup="Application_Startup">
    <Application.Resources>
    </Application.Resources>
</Application>

Then add Application_Startup to the code along with OnExit:

public partial class App : Application
{
    private volatile static Mutex s_mutex;

    private void Application_Startup(object sender, StartupEventArgs e)
    {
        s_mutex = new Mutex(true, @"Global\MenuMutex", out bool grantedOwnership);

        if (!grantedOwnership)
        {
            MessageBox.Show($"Another instance is already running!", "Error", MessageBoxButton.OK, MessageBoxImage.Exclamation);
            Current.Shutdown();
        }
        else
            new MainWindow().Show();
    }

    protected override void OnExit(ExitEventArgs e)
    {
        s_mutex?.ReleaseMutex();
        s_mutex?.Dispose();
        s_mutex = null;
        base.OnExit(e);
    }

Aldus

Answer 4

Write in the Application_Startup:

private void Application_Startup(object sender, StartupEventArgs e)  
{  
    ...
    if (!condition)  
    {  
        e.GetType()  
          .GetProperty("PerformDefaultAction", BindingFlags.Instance | BindingFlags.NonPublic)  
          .SetValue(e, false);  
        Shutdown();  
        return;  
    }  
    ...
}

Katiekatina

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