Application Lifetimes

Not all platforms are created equal! For example, the lifetime management that you may be used to developing with in Windows Forms or WPF can operate only on desktop-style platforms. Avalonia UI is a cross-platform framework; so to make your application portable, it provides several different lifetime models for your application, and also allows you to control everything manually if the target platform permits.

How do lifetimes work?

For a desktop application, you initialise like this:

class Program
{
  // This method is needed for IDE previewer infrastructure
  public static AppBuilder BuildAvaloniaApp() 
    => AppBuilder.Configure<App>().UsePlatformDetect();

  // The entry point. Things aren't ready yet, so at this point
  // you shouldn't use any Avalonia types or anything that expects
  // a SynchronizationContext to be ready
  public static int Main(string[] args) 
    => BuildAvaloniaApp().StartWithClassicDesktopLifetime(args);
}

Then the main window is created in the Application class:

public override void OnFrameworkInitializationCompleted()
{
  if (ApplicationLifetime 
                  is IClassicDesktopStyleApplicationLifetime desktop)
    desktop.MainWindow = new MainWindow();
  else if (ApplicationLifetime 
                  is ISingleViewApplicationLifetime singleView)
    singleView.MainView = new MainView();
  base.OnFrameworkInitializationCompleted();
}

This method is called when the framework has initialized and the ApplicationLifetime property contains the chosen lifetime if any.

к сведению

If you run the application in design mode (this uses the IDE previewer process), then ApplicationLifetime is null.

Lifetime Interfaces

Avalonia UI provides a range of interfaces to allow you to choose a level of control that is suitable for your application. These are provided by the BuildAvaloniaApp().Start[Something] family of methods.

IControlledApplicationLifetime

Provided by:

• StartWithClassicDesktopLifetime
• StartLinuxFramebuffer

Allows you to subscribe to Startup and Exit events and permits explicitly shutting down of the application by calling the Shutdown method. This interface gives you control of the application's exit procedures.

IClassicDesktopStyleApplicationLifetime

Inherits: IControlledApplicationLifetime

Provided by:

• StartWithClassicDesktopLifetime

Allows you to control your application lifetime in the manner of a Windows Forms or WPF application. This interface provides a way to access the list of the currently opened windows, to set a main window, and has three shutdown modes:

• OnLastWindowClose - shuts down the application when the last window is closed
• OnMainWindowClose - shuts down the application when the main window is closed (if it has been set).
• OnExplicitShutdown - disables automatic shutdown of the application, you need to call the Shutdown method in your code.

ISingleViewApplicationLifetime

Provided by:

• StartLinuxFramebuffer
• mobile platforms

Some platforms do not have a concept of a desktop main window and only allow one view on the device's screen at a time. For these platforms the lifetime allows you to set and change the main view class (MainView) instead.

к сведению

To implement the navigation stack on platforms like this (with a single main view), you can use ReactiveUI routing or another routing control.

Manual Lifetime Management

If you need to, you can take full control of your application's lifetime management. For example on a desktop platform you can pass a delegate to AppMain to the BuildAvaloniaApp.Start method, and then manage things manually from there:

class Program
{
  // This method is needed for IDE previewer infrastructure
  public static AppBuilder BuildAvaloniaApp() 
    => AppBuilder.Configure<App>().UsePlatformDetect();

  // The entry point. Things aren't ready yet, so at this point
  // you shouldn't use any Avalonia types or anything that expects
  // a SynchronizationContext to be ready
  public static int Main(string[] args) 
    => BuildAvaloniaApp().Start(AppMain, args);

  // Application entry point. Avalonia is completely initialized.
  static void AppMain(Application app, string[] args)
  {
     // A cancellation token source that will be 
     // used to stop the main loop
     var cts = new CancellationTokenSource();
     
     // Do you startup code here
     new Window().Show();

     // Start the main loop
     app.Run(cts.Token);
  }
}