Implement scene delegate for iOS (#20454)

* Implement scene delegate for iOS

* Move OS check to its own method to make analyzer happy

src/iOS/Avalonia.iOS/AvaloniaAppDelegate.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Runtime.Versioning;
 using Foundation;
 using Avalonia.Controls.ApplicationLifetimes;
 using UIKit;
@@ -27,6 +28,7 @@ namespace Avalonia.iOS
             add { _onActivated += value; }
             remove { _onActivated -= value; }
         }
+
         event EventHandler<ActivatedEventArgs> IAvaloniaAppDelegate.Deactivated
         {
             add { _onDeactivated += value; }
@@ -39,6 +41,17 @@ namespace Avalonia.iOS
         [Export("window")]
         public UIWindow? Window { get; set; }
 
+        [Export("application:configurationForConnectingSceneSession:options:")]
+        [SupportedOSPlatform("ios13.0")]
+        [SupportedOSPlatform("tvos13.0")]
+        [SupportedOSPlatform("maccatalyst")]
+        public UISceneConfiguration GetConfiguration(UIApplication application, UISceneSession connectingSceneSession, UISceneConnectionOptions options)
+        {
+            var config = new UISceneConfiguration(null, connectingSceneSession.Role);
+            config.DelegateType = typeof(AvaloniaSceneDelegate);
+            return config;
+        }
+
         [Export("application:didFinishLaunchingWithOptions:")]
         public bool FinishedLaunching(UIApplication application, NSDictionary? launchOptions)
         {
@@ -46,28 +59,27 @@ namespace Avalonia.iOS
             builder = CustomizeAppBuilder(builder);
 
             var lifetime = new SingleViewLifetime();
-
+            builder.AfterApplicationSetup(_ => CreateAndInitWindow(lifetime));
-            builder.AfterApplicationSetup(_ =>
-            {
-                Window = new UIWindow();
-
-                var view = new AvaloniaView();
-                lifetime.View = view;
-                var controller = new DefaultAvaloniaViewController
-                {
-                    View = view
-                };
-                Window.RootViewController = controller;
-                view.InitWithController(controller);
-            });
-
             builder.SetupWithLifetime(lifetime);
 
-            Window!.MakeKeyAndVisible();
+            Window?.MakeKeyAndVisible();
 
             return true;
         }
 
+        private void CreateAndInitWindow(SingleViewLifetime lifetime)
+        {
+            if (OperatingSystem.IsIOSVersionAtLeast(13) ||
+                OperatingSystem.IsTvOSVersionAtLeast(13) ||
+                OperatingSystem.IsMacCatalyst())
+            {
+                return;
+            }
+
+            Window = new UIWindow();
+            AvaloniaSceneDelegate.InitWindow(Window, lifetime);
+        }
+
         [Export("application:openURL:options:")]
         public bool OpenUrl(UIApplication app, NSUrl url, NSDictionary options)
         {

src/iOS/Avalonia.iOS/AvaloniaSceneDelegate.cs

@@ -0,0 +1,36 @@
+using Foundation;
+using UIKit;
+
+namespace Avalonia.iOS;
+
+internal sealed class AvaloniaSceneDelegate : UIResponder, IUIWindowSceneDelegate
+{
+    [Export("window")]
+    public UIWindow? Window { get; set; }
+
+    [Export("scene:willConnectToSession:options:")]
+    public void WillConnect(UIScene scene, UISceneSession session, UISceneConnectionOptions connectionOptions)
+    {
+        if (session.Configuration.Name is not null ||
+            scene is not UIWindowScene windowScene ||
+            Application.Current?.ApplicationLifetime is not SingleViewLifetime lifetime)
+        {
+            return;
+        }
+
+        Window = new UIWindow(windowScene);
+        InitWindow(Window, lifetime);
+
+        Window.MakeKeyAndVisible();
+    }
+
+    internal static void InitWindow(UIWindow window, SingleViewLifetime lifetime)
+    {
+        var view = new AvaloniaView();
+        lifetime.View = view;
+
+        var controller = new DefaultAvaloniaViewController { View = view };
+        window.RootViewController = controller;
+        view.InitWithController(controller);
+    }
+}

src/iOS/Avalonia.iOS/SingleViewLifetime.cs

@@ -1,6 +1,4 @@
-using System;
+using Avalonia.Controls;
-using System.Diagnostics.CodeAnalysis;
-using Avalonia.Controls;
 using Avalonia.Controls.ApplicationLifetimes;
 
 namespace Avalonia.iOS;
@@ -10,9 +8,9 @@ internal class SingleViewLifetime : ISingleViewApplicationLifetime, ISingleTopLe
     private Control? _mainView;
     private AvaloniaView? _view;
 
-    public AvaloniaView View
+    public AvaloniaView? View
     {
-        [return: MaybeNull] get => _view!;
+        get => _view;
         internal set
         {
             if (_view != null)
@@ -21,7 +19,7 @@ internal class SingleViewLifetime : ISingleViewApplicationLifetime, ISingleTopLe
                 _view.Dispose();
             }
             _view = value;
-            _view.Content = _mainView;
+            _view?.Content = _mainView;
         }
     }
 
@@ -33,10 +31,7 @@ internal class SingleViewLifetime : ISingleViewApplicationLifetime, ISingleTopLe
             if (_mainView != value)
             {
                 _mainView = value;
-                if (_view != null)
+                _view?.Content = _mainView;
-                {
-                    _view.Content = _mainView;
-                }
             }
         }
     }