Fix init order of SetupWithClassicDesktopLifetime

src/Avalonia.Controls/AppBuilder.cs

@@ -353,12 +353,21 @@ private void Setup()
             SetupUnsafe();
         }
 
+        /// <summary>
+        /// Allows <see cref="Setup"/> to be called again after it has already been called once.
+        /// </summary>
+        internal static void ResetSetupForUnitTests()
+            => s_setupWasAlreadyCalled = false;
+
         /// <summary>
         /// Setup method that doesn't check for input initalizers being set.
         /// Nor 
         /// </summary>
         internal void SetupUnsafe()
         {
+            var setupLifetime = _lifetime as ISetupApplicationLifetime;
+            setupLifetime?.BeforeAppInit();
+
             _optionsInitializers?.Invoke();
             RuntimePlatformServicesInitializer?.Invoke();
             TextShapingSubsystemInitializer?.Invoke();
@@ -373,6 +382,8 @@ internal void SetupUnsafe()
             AfterApplicationSetupCallback?.Invoke(Self);
             AfterSetupCallback?.Invoke(Self);
             Instance.OnFrameworkInitializationCompleted();
+
+            setupLifetime?.AfterAppInit();
         }
     }
 }

src/Avalonia.Controls/ApplicationLifetimes/ClassicDesktopStyleApplicationLifetime.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Runtime.CompilerServices;
 using System.Threading;
 using Avalonia.Collections;
@@ -12,13 +13,19 @@
 
 namespace Avalonia.Controls.ApplicationLifetimes
 {
-    public class ClassicDesktopStyleApplicationLifetime : IClassicDesktopStyleApplicationLifetime, IDisposable
+    public class ClassicDesktopStyleApplicationLifetime :
+        IClassicDesktopStyleApplicationLifetime,
+        ISetupApplicationLifetime,
+        IDisposable
     {
         private int _exitCode;
         private CancellationTokenSource? _cts;
         private bool _isShuttingDown;
         private readonly AvaloniaList<Window> _windows = new();
-        private CompositeDisposable? _compositeDisposable; 
+        private CompositeDisposable? _globalEventsSubscriptions;
+        private bool _beforeInitCalled;
+        private bool _afterInitCalled;
+        private IPlatformLifetimeEventsImpl? _platformLifetimeEventsImpl;
 
         /// <inheritdoc/>
         public event EventHandler<ControlledApplicationLifetimeStartupEventArgs>? Startup;
@@ -67,16 +74,11 @@ public bool TryShutdown(int exitCode = 0)
             return DoShutdown(new ShutdownRequestedEventArgs(), true, false, exitCode);
         }
 
-        internal void SubscribeGlobalEvents()
+        private void SubscribeGlobalEvents()
         {
-            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;
-            }
+            Debug.Assert(_globalEventsSubscriptions is null);
 
-            _compositeDisposable = new CompositeDisposable(
+            _globalEventsSubscriptions = new CompositeDisposable(
                 Window.WindowOpenedEvent.AddClassHandler(typeof(Window), (sender, _) =>
                 {
                     var window = (Window)sender!;
@@ -93,16 +95,32 @@ internal void SubscribeGlobalEvents()
                 }));            
         }
 
-        internal void SetupCore(string[] args)
+        private void BeforeInit()
         {
+            if (_beforeInitCalled)
+                return;
+
+            _beforeInitCalled = true;
             SubscribeGlobalEvents();
+        }
 
-            Startup?.Invoke(this, new ControlledApplicationLifetimeStartupEventArgs(args));
+        void ISetupApplicationLifetime.BeforeAppInit()
+            => BeforeInit();
 
-            var lifetimeEvents = AvaloniaLocator.Current.GetService<IPlatformLifetimeEventsImpl>(); 
+        private void AfterInit()
+        {
+            if (_afterInitCalled)
+                return;
 
-            if (lifetimeEvents != null)
-                lifetimeEvents.ShutdownRequested += OnShutdownRequested;
+            _afterInitCalled = true;
+
+            _platformLifetimeEventsImpl = AvaloniaLocator.Current.GetService<IPlatformLifetimeEventsImpl>();
+            _platformLifetimeEventsImpl?.ShutdownRequested += OnShutdownRequested;
+        }
+
+        void ISetupApplicationLifetime.AfterAppInit()
+        {
+            AfterInit();
         }
 
         public int Start(string[] args)
@@ -121,7 +139,11 @@ public int Start()
 
         internal int StartCore(string[] args)
         {
-            SetupCore(args);
+            // Before/AfterInit should have been called from ISetupApplicationLifetime.
+            // If somehow they weren't (e.g., for a manually started lifetime), do it now.
+            BeforeInit();
+            AfterInit();
+            Startup?.Invoke(this, new ControlledApplicationLifetimeStartupEventArgs(args));
 
             _cts = new CancellationTokenSource();
 
@@ -143,8 +165,11 @@ private void ShowMainWindow()
 
         public void Dispose()
         {
-            _compositeDisposable?.Dispose();
-            _compositeDisposable = null;
+            _globalEventsSubscriptions?.Dispose();
+            _globalEventsSubscriptions = null;
+
+            _platformLifetimeEventsImpl?.ShutdownRequested -= OnShutdownRequested;
+            _platformLifetimeEventsImpl = null;
         }
 
         private bool DoShutdown(
@@ -222,15 +247,12 @@ namespace Avalonia
     /// </summary>
     public static class ClassicDesktopStyleApplicationLifetimeExtensions
     {
-        private static ClassicDesktopStyleApplicationLifetime PrepareLifetime(AppBuilder builder, string[] args,
+        private static ClassicDesktopStyleApplicationLifetime CreateLifetime(
+            string[] args,
             Action<IClassicDesktopStyleApplicationLifetime>? lifetimeBuilder)
         {
-            var lifetime = new ClassicDesktopStyleApplicationLifetime();
-            lifetime.SubscribeGlobalEvents();
-
-            lifetime.Args = args;
+            var lifetime = new ClassicDesktopStyleApplicationLifetime { Args = args };
             lifetimeBuilder?.Invoke(lifetime);
-
             return lifetime;
         }
 
@@ -244,8 +266,7 @@ private static ClassicDesktopStyleApplicationLifetime PrepareLifetime(AppBuilder
         public static AppBuilder SetupWithClassicDesktopLifetime(this AppBuilder builder, string[] args,
             Action<IClassicDesktopStyleApplicationLifetime>? lifetimeBuilder = null)
         {
-            var lifetime = PrepareLifetime(builder, args, lifetimeBuilder);
-            lifetime.SetupCore(args);
+            var lifetime = CreateLifetime(args, lifetimeBuilder);
             return builder.SetupWithLifetime(lifetime);
         }
 
@@ -260,7 +281,7 @@ public static int StartWithClassicDesktopLifetime(
             this AppBuilder builder, string[] args,
             Action<IClassicDesktopStyleApplicationLifetime>? lifetimeBuilder = null)
         {
-            var lifetime = PrepareLifetime(builder, args, lifetimeBuilder);
+            var lifetime = CreateLifetime(args, lifetimeBuilder);
             builder.SetupWithLifetime(lifetime);
             return lifetime.Start(args);
         }
@@ -275,7 +296,7 @@ public static int StartWithClassicDesktopLifetime(
         public static int StartWithClassicDesktopLifetime(
             this AppBuilder builder, string[] args, ShutdownMode shutdownMode)
         {
-            var lifetime = PrepareLifetime(builder, args, l => l.ShutdownMode = shutdownMode);
+            var lifetime = CreateLifetime(args, l => l.ShutdownMode = shutdownMode);
             builder.SetupWithLifetime(lifetime);
             return lifetime.Start(args);
         }

src/Avalonia.Controls/ApplicationLifetimes/ISetupApplicationLifetime.cs

@@ -0,0 +1,17 @@
+namespace Avalonia.Controls.ApplicationLifetimes;
+
+/// <summary>
+/// An interface for lifetimes that need to execute extra code before and after initialization.
+/// </summary>
+internal interface ISetupApplicationLifetime
+{
+    /// <summary>
+    /// Called before anything is initialized: platforms, rendering, app, etc. aren't available yet.
+    /// </summary>
+    void BeforeAppInit();
+
+    /// <summary>
+    /// Called after the app has been initialized.
+    /// </summary>
+    void AfterAppInit();
+}