Make Classic ApplicationLifetime API a bit more reliable (#14267)

      * Add StartWithClassicDesktopLifetime overload with a lifetime builder

* Disallow changing Application.ApplicationLifetime after setup was completed

* Avoid static dependency on a singleton lifetime

* Introduce SetupWithClassicDesktopLifetime method

* Move more logic from Start method to Setup

* Add docs

* Avoid public API changes

* Fix tests

* Repalce locator usage with `.UseLifetimeOverride`

---------

Co-authored-by: Benedikt Stebner <[email protected]>

Author: maxkatz6

src/Avalonia.Controls/AppBuilder.cs

@@ -6,6 +6,7 @@
 using Avalonia.Platform;
 using Avalonia.Media.Fonts;
 using Avalonia.Media;
+using Avalonia.Metadata;
 
 namespace Avalonia
 {
@@ -54,6 +55,11 @@ public sealed class AppBuilder
         /// </summary>
         public Action? RenderingSubsystemInitializer { get; private set; }
 
+        /// <summary>
+        /// Gets a method to override a lifetime factory.
+        /// </summary>
+        public Func<Type, IApplicationLifetime?>? LifetimeOverride { get; private set; }
+
         /// <summary>
         /// Gets the name of the currently selected rendering subsystem.
         /// </summary>
@@ -238,6 +244,13 @@ public AppBuilder UseStandardRuntimePlatformSubsystem()
             return Self;
         }
 
+        [PrivateApi]
+        public AppBuilder UseLifetimeOverride(Func<Type, IApplicationLifetime?> func)
+        {
+            LifetimeOverride = func;
+            return Self;
+        }
+
         /// <summary>
         /// Configures platform-specific options
         /// </summary>

src/Avalonia.Controls/Application.cs

@@ -42,6 +42,8 @@ public class Application : AvaloniaObject, IDataContextProvider, IGlobalDataTemp
         private bool _notifyingResourcesChanged;
         private Action<IReadOnlyList<IStyle>>? _stylesAdded;
         private Action<IReadOnlyList<IStyle>>? _stylesRemoved;
+        private IApplicationLifetime? _applicationLifetime;
+        private bool _setupCompleted;
 
         /// <summary>
         /// Defines the <see cref="DataContext"/> property.
@@ -60,7 +62,7 @@ public class Application : AvaloniaObject, IDataContextProvider, IGlobalDataTemp
         /// <inheritdoc/>
         public event EventHandler<ResourcesChangedEventArgs>? ResourcesChanged;
 
-        /// <inheritdoc/>
+        [Obsolete("Cast ApplicationLifetime to IActivatableApplicationLifetime instead.")]
         public event EventHandler<UrlOpenedEventArgs>? UrlsOpened;
 
         /// <inheritdoc/>
@@ -170,15 +172,28 @@ public IResourceDictionary Resources
 
         /// <inheritdoc/>
         bool IStyleHost.IsStylesInitialized => _styles != null;
-       
+
         /// <summary>
         /// Application lifetime, use it for things like setting the main window and exiting the app from code
         /// Currently supported lifetimes are:
         /// - <see cref="IClassicDesktopStyleApplicationLifetime"/>
         /// - <see cref="ISingleViewApplicationLifetime"/>
         /// - <see cref="IControlledApplicationLifetime"/> 
+        /// - <see cref="IActivatableApplicationLifetime"/> 
         /// </summary>
-        public IApplicationLifetime? ApplicationLifetime { get; set; }
+        public IApplicationLifetime? ApplicationLifetime
+        {
+            get => _applicationLifetime;
+            set
+            {
+                if (_setupCompleted)
+                {
+                    throw new InvalidOperationException($"It's not possible to change {nameof(ApplicationLifetime)} after Application was initialized.");
+                }
+
+                _applicationLifetime = value;
+            }
+        }
 
         /// <summary>
         /// Represents a contract for accessing global platform-specific settings.
@@ -207,7 +222,7 @@ event Action<IReadOnlyList<IStyle>>? IGlobalStyles.GlobalStylesRemoved
         /// Initializes the application by loading XAML etc.
         /// </summary>
         public virtual void Initialize() { }
-
+        
         /// <inheritdoc/>
         public bool TryGetResource(object key, ThemeVariant? theme, out object? value)
         {
@@ -263,13 +278,15 @@ public virtual void RegisterServices()
 
             AvaloniaLocator.CurrentMutable.Bind<IGlobalClock>()
                 .ToConstant(MediaContext.Instance.Clock);
+
+            _setupCompleted = true;
         }
 
         public virtual void OnFrameworkInitializationCompleted()
         {
         }
 
-        void  IApplicationPlatformEvents.RaiseUrlsOpened(string[] urls)
+        void IApplicationPlatformEvents.RaiseUrlsOpened(string[] urls)
         {
             UrlsOpened?.Invoke(this, new UrlOpenedEventArgs (urls));
         }

src/Avalonia.Controls/ApplicationLifetimes/ClassicDesktopStyleApplicationLifetime.cs

@@ -8,6 +8,7 @@
 using Avalonia.Controls.ApplicationLifetimes;
 using Avalonia.Interactivity;
 using Avalonia.Platform;
+using Avalonia.Reactive;
 using Avalonia.Threading;
 
 namespace Avalonia.Controls.ApplicationLifetimes
@@ -18,38 +19,7 @@ public class ClassicDesktopStyleApplicationLifetime : IClassicDesktopStyleApplic
         private CancellationTokenSource? _cts;
         private bool _isShuttingDown;
         private readonly AvaloniaList<Window> _windows = new();
-
-        private static ClassicDesktopStyleApplicationLifetime? s_activeLifetime;
-
-        static ClassicDesktopStyleApplicationLifetime()
-        {
-            Window.WindowOpenedEvent.AddClassHandler(typeof(Window), OnWindowOpened);
-            Window.WindowClosedEvent.AddClassHandler(typeof(Window), OnWindowClosed);
-        }
-
-        private static void OnWindowClosed(object? sender, RoutedEventArgs e)
-        {
-            var window = (Window)sender!;
-            s_activeLifetime?._windows.Remove(window);
-            s_activeLifetime?.HandleWindowClosed(window);
-        }
-
-        private static void OnWindowOpened(object? sender, RoutedEventArgs e)
-        {
-            var window = (Window)sender!;
-            if (s_activeLifetime is not null && !s_activeLifetime._windows.Contains(window))
-            {
-                s_activeLifetime._windows.Add(window);
-            }
-        }
-
-        public ClassicDesktopStyleApplicationLifetime()
-        {
-            if (s_activeLifetime != null)
-                throw new InvalidOperationException(
-                    "Can not have multiple active ClassicDesktopStyleApplicationLifetime instances and the previously created one was not disposed");
-            s_activeLifetime = this;
-        }
+        private CompositeDisposable? _compositeDisposable; 
 
         /// <inheritdoc/>
         public event EventHandler<ControlledApplicationLifetimeStartupEventArgs>? Startup;
@@ -97,9 +67,32 @@ public bool TryShutdown(int exitCode = 0)
         {
             return DoShutdown(new ShutdownRequestedEventArgs(), true, false, exitCode);
         }
-        
-        public int Start(string[] args)
+
+        internal void SetupCore(string[] args)
         {
+            if (_compositeDisposable is not null)
+            {
+                // There could be a case, when lifetime was setup without starting.
+                // Until developer started it manually later. To avoid API breaking changes, it will execute Setup method twice.
+                return;
+            }
+            
+            _compositeDisposable = new CompositeDisposable(
+                Window.WindowOpenedEvent.AddClassHandler(typeof(Window), (sender, _) =>
+                {
+                    var window = (Window)sender!;
+                    if (!_windows.Contains(window))
+                    {
+                        _windows.Add(window);
+                    }
+                }),
+                Window.WindowClosedEvent.AddClassHandler(typeof(Window), (sender, _) =>
+                {
+                    var window = (Window)sender!;
+                    _windows.Remove(window);
+                    HandleWindowClosed(window);
+                }));
+
             Startup?.Invoke(this, new ControlledApplicationLifetimeStartupEventArgs(args));
 
             var options = AvaloniaLocator.Current.GetService<ClassicDesktopStyleApplicationLifetimeOptions>();
@@ -116,9 +109,14 @@ public int Start(string[] args)
 
             if (lifetimeEvents != null)
                 lifetimeEvents.ShutdownRequested += OnShutdownRequested;
+        }
 
-            _cts = new CancellationTokenSource();
+        public int Start(string[] args)
+        {
+            SetupCore(args);
 
+            _cts = new CancellationTokenSource();
+
             // Note due to a bug in the JIT we wrap this in a method, otherwise MainWindow
             // gets stuffed into a local var and can not be GCed until after the program stops.
             // this method never exits until program end.
@@ -137,8 +135,8 @@ private void ShowMainWindow()
 
         public void Dispose()
         {
-            if (s_activeLifetime == this)
-                s_activeLifetime = null;
+            _compositeDisposable?.Dispose();
+            _compositeDisposable = null;
         }
 
         private bool DoShutdown(
@@ -206,21 +204,65 @@ public class ClassicDesktopStyleApplicationLifetimeOptions
 
 namespace Avalonia
 {
+    /// <summary>
+    /// IClassicDesktopStyleApplicationLifetime related AppBuilder extensions.
+    /// </summary>
     public static class ClassicDesktopStyleApplicationLifetimeExtensions
     {
-        public static int StartWithClassicDesktopLifetime(
-            this AppBuilder builder, string[] args, ShutdownMode shutdownMode = ShutdownMode.OnLastWindowClose)
+        private static ClassicDesktopStyleApplicationLifetime PrepareLifetime(AppBuilder builder, string[] args,
+            Action<IClassicDesktopStyleApplicationLifetime>? lifetimeBuilder)
         {
-            var lifetime = AvaloniaLocator.Current.GetService<ClassicDesktopStyleApplicationLifetime>();
-
-            if (lifetime == null)
-            {
-                lifetime = new ClassicDesktopStyleApplicationLifetime();
-            }
+            var lifetime = builder.LifetimeOverride?.Invoke(typeof(ClassicDesktopStyleApplicationLifetime)) as ClassicDesktopStyleApplicationLifetime 
+                ?? new ClassicDesktopStyleApplicationLifetime();
 
             lifetime.Args = args;
-            lifetime.ShutdownMode = shutdownMode;
+            lifetimeBuilder?.Invoke(lifetime);
+
+            return lifetime;
+        }
+
+        /// <summary>
+        /// Setups the Application with a IClassicDesktopStyleApplicationLifetime, but doesn't show the main window and doesn't run application main loop.
+        /// </summary>
+        /// <param name="builder">Application builder.</param>
+        /// <param name="args">Startup arguments.</param>
+        /// <param name="lifetimeBuilder">Lifetime builder to modify the lifetime before application started.</param>
+        /// <returns>Exit code.</returns>
+        public static AppBuilder SetupWithClassicDesktopLifetime(this AppBuilder builder, string[] args,
+            Action<IClassicDesktopStyleApplicationLifetime>? lifetimeBuilder = null)
+        {
+            var lifetime = PrepareLifetime(builder, args, lifetimeBuilder);
+            lifetime.SetupCore(args);
+            return builder.SetupWithLifetime(lifetime);
+        }
+
+        /// <summary>
+        /// Starts the Application with a IClassicDesktopStyleApplicationLifetime, shows main window and runs application main loop.
+        /// </summary>
+        /// <param name="builder">Application builder.</param>
+        /// <param name="args">Startup arguments.</param>
+        /// <param name="lifetimeBuilder">Lifetime builder to modify the lifetime before application started.</param>
+        /// <returns>Exit code.</returns>
+        public static int StartWithClassicDesktopLifetime(
+            this AppBuilder builder, string[] args,
+            Action<IClassicDesktopStyleApplicationLifetime>? lifetimeBuilder = null)
+        {
+            var lifetime = PrepareLifetime(builder, args, lifetimeBuilder);
+            builder.SetupWithLifetime(lifetime);
+            return lifetime.Start(args);
+        }
 
+        /// <summary>
+        /// Starts the Application with a IClassicDesktopStyleApplicationLifetime, shows main window and runs application main loop.
+        /// </summary>
+        /// <param name="builder">Application builder.</param>
+        /// <param name="args">Startup arguments.</param>
+        /// <param name="shutdownMode">Lifetime shutdown mode.</param>
+        /// <returns>Exit code.</returns>
+        public static int StartWithClassicDesktopLifetime(
+            this AppBuilder builder, string[] args, ShutdownMode shutdownMode)
+        {
+            var lifetime = PrepareLifetime(builder, args, l => l.ShutdownMode = shutdownMode);
             builder.SetupWithLifetime(lifetime);
             return lifetime.Start(args);
         }

src/Avalonia.Native/AvaloniaNativePlatformExtensions.cs

@@ -13,20 +13,19 @@ public static AppBuilder UseAvaloniaNative(this AppBuilder builder)
             builder
                 .UseStandardRuntimePlatformSubsystem()
                 .UseWindowingSubsystem(() =>
-            {
-                var platform = AvaloniaNativePlatform.Initialize(
-                    AvaloniaLocator.Current.GetService<AvaloniaNativePlatformOptions>() ??
-                    new AvaloniaNativePlatformOptions());
+                {
+                    var platform = AvaloniaNativePlatform.Initialize(
+                        AvaloniaLocator.Current.GetService<AvaloniaNativePlatformOptions>() ??
+                        new AvaloniaNativePlatformOptions());
 
-                    builder.AfterSetup (x=>
-                    {
-                        platform.SetupApplicationName();
-                        platform.SetupApplicationMenuExporter();
-                    });
-            });
-
-            AvaloniaLocator.CurrentMutable.Bind<ClassicDesktopStyleApplicationLifetime>()
-                .ToConstant(new MacOSClassicDesktopStyleApplicationLifetime());
+                        builder.AfterSetup (x=>
+                        {
+                            platform.SetupApplicationName();
+                            platform.SetupApplicationMenuExporter();
+                        });
+                })
+                .UseLifetimeOverride(type => type == typeof(ClassicDesktopStyleApplicationLifetime)
+                    ? new MacOSClassicDesktopStyleApplicationLifetime() : null);
 
             return builder;
         }