Make root automation node come from OS.

This will be needed for OSX.

src/Avalonia.Controls/Automation/Peers/AutomationPeer.cs

@@ -66,6 +66,17 @@ namespace Avalonia.Automation.Peers
             Node = factory.CreateNode(this);
         }
 
+        /// <summary>
+        /// Initializes a new instance of the <see cref="AutomationPeer"/> class.
+        /// </summary>
+        /// <param name="node">
+        /// The platform automation node.
+        /// </param>
+        protected AutomationPeer(IAutomationNode node)
+        {
+            Node = node;
+        }
+
         /// <summary>
         /// Gets the related node in the platform UI Automation tree.
         /// </summary>

src/Avalonia.Controls/Automation/Peers/ControlAutomationPeer.cs

@@ -23,10 +23,14 @@ namespace Avalonia.Automation.Peers
             : base(factory)
         {
             Owner = owner ?? throw new ArgumentNullException("owner");
+            Initialize();
+        }
 
-            owner.PropertyChanged += OwnerPropertyChanged;
-            var visualChildren = ((IVisual)owner).VisualChildren;
-            visualChildren.CollectionChanged += VisualChildrenChanged;
+        protected ControlAutomationPeer(IAutomationNode node, Control owner)
+            : base(node)
+        {
+            Owner = owner ?? throw new ArgumentNullException("owner");
+            Initialize();
         }
 
         public Control Owner { get; }
@@ -161,11 +165,18 @@ namespace Avalonia.Automation.Peers
         protected override bool IsKeyboardFocusableCore() => Owner.Focusable;
         protected override void SetFocusCore() => Owner.Focus();
 
-        private Rect GetBounds(TransformedBounds? bounds)
+        private static Rect GetBounds(TransformedBounds? bounds)
         {
             return bounds?.Bounds.TransformToAABB(bounds!.Value.Transform) ?? default;
         }
 
+        private void Initialize()
+        {
+            Owner.PropertyChanged += OwnerPropertyChanged;
+            var visualChildren = ((IVisual)Owner).VisualChildren;
+            visualChildren.CollectionChanged += VisualChildrenChanged;
+        }
+
         private void VisualChildrenChanged(object sender, EventArgs e) => InvalidateChildren();
 
         private void OwnerPropertyChanged(object sender, AvaloniaPropertyChangedEventArgs e)

src/Avalonia.Controls/Automation/Peers/PopupRootAutomationPeer.cs

@@ -8,8 +8,8 @@ namespace Avalonia.Automation.Peers
 {
     public class PopupRootAutomationPeer : WindowBaseAutomationPeer
     {
-        public PopupRootAutomationPeer(IAutomationNodeFactory factory, PopupRoot owner)
-            : base(factory, owner)
+        public PopupRootAutomationPeer(IAutomationNode node, PopupRoot owner)
+            : base(node, owner)
         {
             if (owner.IsVisible)
                 StartTrackingFocus();

src/Avalonia.Controls/Automation/Peers/WindowAutomationPeer.cs

@@ -8,8 +8,8 @@ namespace Avalonia.Automation.Peers
 {
     public class WindowAutomationPeer : WindowBaseAutomationPeer
     {
-        public WindowAutomationPeer(IAutomationNodeFactory factory, Window owner)
-            : base(factory, owner)
+        public WindowAutomationPeer(IAutomationNode node, Window owner)
+            : base(node, owner)
         {
             if (owner.IsVisible)
                 StartTrackingFocus();

src/Avalonia.Controls/Automation/Peers/WindowBaseAutomationPeer.cs

@@ -14,8 +14,8 @@ namespace Avalonia.Automation.Peers
     {
         private Control? _focus;
 
-        public WindowBaseAutomationPeer(IAutomationNodeFactory factory, WindowBase owner)
-            : base(factory, owner)
+        public WindowBaseAutomationPeer(IAutomationNode node, WindowBase owner)
+            : base(node, owner)
         {
         }
 

src/Avalonia.Controls/Control.cs

@@ -209,5 +209,12 @@ namespace Avalonia.Controls
             _automationPeer = OnCreateAutomationPeer(factory);
             return _automationPeer;
         }
+
+        internal void SetAutomationPeer(AutomationPeer peer)
+        {
+            if (_automationPeer is object)
+                throw new InvalidOperationException("Automation peer is already set.");
+            _automationPeer = peer ?? throw new ArgumentNullException(nameof(peer));
+        }
     }
 }

src/Avalonia.Controls/Platform/IWindowBaseImpl.cs

@@ -1,4 +1,6 @@
 using System;
+using Avalonia.Automation.Peers;
+using Avalonia.Automation.Platform;
 
 namespace Avalonia.Platform
 {
@@ -44,6 +46,11 @@ namespace Avalonia.Platform
         /// </summary>
         Action Activated { get; set; }
 
+        /// <summary>
+        /// Gets or sets a method called when automation is started on the window.
+        /// </summary>
+        Func<IAutomationNode, AutomationPeer> AutomationStarted { get; set; }
+
         /// <summary>
         /// Gets the platform window handle.
         /// </summary>

src/Avalonia.Controls/Primitives/PopupRoot.cs

@@ -171,9 +171,9 @@ namespace Avalonia.Controls.Primitives
             }
         }
 
-        protected override AutomationPeer OnCreateAutomationPeer(IAutomationNodeFactory factory)
+        protected override AutomationPeer OnCreateAutomationPeer(IAutomationNode node)
         {
-            return new PopupRootAutomationPeer(factory, this);
+            return new PopupRootAutomationPeer(node, this);
         }
     }
 }

src/Avalonia.Controls/TopLevel.cs

@@ -1,5 +1,7 @@
 using System;
 using System.Reactive.Linq;
+using Avalonia.Automation.Peers;
+using Avalonia.Automation.Platform;
 using Avalonia.Controls.Platform;
 using Avalonia.Controls.Primitives;
 using Avalonia.Input;

src/Avalonia.Controls/Window.cs

@@ -968,9 +968,9 @@ namespace Avalonia.Controls
             }
         }
 
-        protected override AutomationPeer OnCreateAutomationPeer(IAutomationNodeFactory factory)
+        protected override AutomationPeer OnCreateAutomationPeer(IAutomationNode node)
         {
-            return new WindowAutomationPeer(factory, this);
+            return new WindowAutomationPeer(node, this);
         }
     }
 }

src/Avalonia.Controls/WindowBase.cs

@@ -3,6 +3,8 @@ using System.ComponentModel;
 using System.Linq;
 using System.Reactive.Disposables;
 using System.Reactive.Linq;
+using Avalonia.Automation.Peers;
+using Avalonia.Automation.Platform;
 using Avalonia.Controls.Primitives;
 using Avalonia.Input;
 using Avalonia.Layout;
@@ -64,6 +66,7 @@ namespace Avalonia.Controls
             impl.Activated = HandleActivated;
             impl.Deactivated = HandleDeactivated;
             impl.PositionChanged = HandlePositionChanged;
+            impl.AutomationStarted = HandleAutomationStarted;
         }
 
         /// <summary>
@@ -269,6 +272,17 @@ namespace Avalonia.Controls
         /// <returns>The actual size of the window.</returns>
         protected virtual Size ArrangeSetBounds(Size size) => size;
 
+        protected sealed override AutomationPeer OnCreateAutomationPeer(IAutomationNodeFactory factory)
+        {
+            throw new NotSupportedException(
+                "Automation peer for window controls must be created by the operating system.");
+        }
+
+        protected virtual AutomationPeer OnCreateAutomationPeer(IAutomationNode node)
+        {
+            throw new NotImplementedException("OnCreateAutomationPeer must be implemented in a derived class.");
+        }
+
         /// <summary>
         /// Handles a window position change notification from 
         /// <see cref="IWindowBaseImpl.PositionChanged"/>.
@@ -306,6 +320,13 @@ namespace Avalonia.Controls
             Deactivated?.Invoke(this, EventArgs.Empty);
         }
 
+        private AutomationPeer HandleAutomationStarted(IAutomationNode node)
+        {
+            var peer = OnCreateAutomationPeer(node);
+            SetAutomationPeer(peer);
+            return peer;
+        }
+
         private void IsVisibleChanged(AvaloniaPropertyChangedEventArgs e)
         {
             if (!_ignoreVisibilityChange)

src/Avalonia.DesignerSupport/Remote/PreviewerWindowImpl.cs

@@ -1,5 +1,7 @@
 using System;
 using System.Reactive.Disposables;
+using Avalonia.Automation.Peers;
+using Avalonia.Automation.Platform;
 using Avalonia.Controls;
 using Avalonia.Controls.Remote.Server;
 using Avalonia.Input;
@@ -45,6 +47,7 @@ namespace Avalonia.DesignerSupport.Remote
         public IPlatformHandle Handle { get; }
         public WindowState WindowState { get; set; }
         public Action<WindowState> WindowStateChanged { get; set; }
+        public Func<IAutomationNode, AutomationPeer> AutomationStarted { get; set; }
         public Size MaxAutoSizeHint { get; } = new Size(4096, 4096);
 
         protected override void OnMessage(IAvaloniaRemoteTransportConnection transport, object obj)

src/Avalonia.DesignerSupport/Remote/Stubs.cs

@@ -3,6 +3,8 @@ using System.Collections.Generic;
 using System.IO;
 using System.Reactive.Disposables;
 using System.Threading.Tasks;
+using Avalonia.Automation.Peers;
+using Avalonia.Automation.Platform;
 using Avalonia.Controls;
 using Avalonia.Controls.Platform;
 using Avalonia.Controls.Primitives.PopupPositioning;
@@ -38,6 +40,7 @@ namespace Avalonia.DesignerSupport.Remote
         public Action<PixelPoint> PositionChanged { get; set; }
         public WindowState WindowState { get; set; }
         public Action<WindowState> WindowStateChanged { get; set; }
+        public Func<IAutomationNode, AutomationPeer> AutomationStarted { get; set; }
 
         public Action<WindowTransparencyLevel> TransparencyLevelChanged { get; set; }        
 

src/Avalonia.Headless/HeadlessWindowImpl.cs

@@ -1,6 +1,8 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using Avalonia.Automation.Peers;
+using Avalonia.Automation.Platform;
 using Avalonia.Controls;
 using Avalonia.Controls.Platform.Surfaces;
 using Avalonia.Controls.Primitives.PopupPositioning;
@@ -142,6 +144,7 @@ namespace Avalonia.Headless
         public IScreenImpl Screen { get; } = new HeadlessScreensStub();
         public WindowState WindowState { get; set; }
         public Action<WindowState> WindowStateChanged { get; set; }
+        public Func<IAutomationNode, AutomationPeer> AutomationStarted { get; set; }
         public void SetTitle(string title)
         {
 

src/Avalonia.Native/WindowImplBase.cs

@@ -2,6 +2,8 @@ using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Runtime.InteropServices;
+using Avalonia.Automation.Peers;
+using Avalonia.Automation.Platform;
 using Avalonia.Controls;
 using Avalonia.Controls.Platform;
 using Avalonia.Controls.Platform.Surfaces;
@@ -466,5 +468,6 @@ namespace Avalonia.Native
         public AcrylicPlatformCompensationLevels AcrylicCompensationLevels { get; } = new AcrylicPlatformCompensationLevels(1, 0, 0);
 
         public IPlatformHandle Handle { get; private set; }
+        public Func<IAutomationNode, AutomationPeer> AutomationStarted { get; set; }
     }
 }

src/Avalonia.X11/X11Window.cs

@@ -6,6 +6,8 @@ using System.Linq;
 using System.Reactive.Disposables;
 using System.Text;
 using System.Threading.Tasks;
+using Avalonia.Automation.Peers;
+using Avalonia.Automation.Platform;
 using Avalonia.Controls;
 using Avalonia.Controls.Platform;
 using Avalonia.Controls.Primitives.PopupPositioning;
@@ -1128,5 +1130,6 @@ namespace Avalonia.X11
         public AcrylicPlatformCompensationLevels AcrylicCompensationLevels { get; } = new AcrylicPlatformCompensationLevels(1, 0.8, 0.8);
 
         public bool NeedsManagedDecorations => false;
+        public Func<IAutomationNode, AutomationPeer> AutomationStarted { get; set; }
     }
 }

src/Windows/Avalonia.Win32/Automation/AutomationNode.cs

@@ -56,7 +56,13 @@ namespace Avalonia.Win32.Automation
             Peer = peer;
         }
 
-        public AutomationPeer Peer { get; }
+        protected AutomationNode(Func<IAutomationNode, AutomationPeer> peerGetter)
+        {
+            _runtimeId = new int[] { 3, GetHashCode() };
+            Peer = peerGetter(this);
+        }
+
+        public AutomationPeer Peer { get; protected set; }
         public IAutomationNodeFactory Factory => AutomationNodeFactory.Instance;
 
         public Rect BoundingRectangle

src/Windows/Avalonia.Win32/Automation/AutomationNodeFactory.cs

@@ -1,6 +1,5 @@
 using Avalonia.Automation.Peers;
 using Avalonia.Automation.Platform;
-using Avalonia.Automation.Provider;
 using Avalonia.Threading;
 
 #nullable enable
@@ -14,7 +13,7 @@ namespace Avalonia.Win32.Automation
         public IAutomationNode CreateNode(AutomationPeer peer)
         {
             Dispatcher.UIThread.VerifyAccess();
-            return peer is IRootProvider ? new RootAutomationNode(peer) : new AutomationNode(peer);
+            return new AutomationNode(peer);
         }
     }
 }

src/Windows/Avalonia.Win32/Automation/RootAutomationNode.cs

@@ -13,8 +13,8 @@ namespace Avalonia.Win32.Automation
         IRawElementProviderFragmentRoot,
         IRootAutomationNode
     {
-        public RootAutomationNode(AutomationPeer peer)
-            : base(peer)
+        public RootAutomationNode(Func<IAutomationNode, AutomationPeer> peerGetter)
+            : base(peerGetter)
         {
         }
 

src/Windows/Avalonia.Win32/WindowImpl.AppWndProc.cs

@@ -4,6 +4,7 @@ using System.Runtime.InteropServices;
 using Avalonia.Controls;
 using Avalonia.Input;
 using Avalonia.Input.Raw;
+using Avalonia.Win32.Automation;
 using Avalonia.Win32.Input;
 using Avalonia.Win32.Interop.Automation;
 using static Avalonia.Win32.Interop.UnmanagedMethods;
@@ -76,7 +77,7 @@ namespace Avalonia.Win32
 
                 case WindowsMessage.WM_DESTROY:
                     {
-                        if (_automationProvider is object)
+                        if (_automationNode is object)
                             UiaCoreProviderApi.UiaReturnRawElementProvider(_hwnd, IntPtr.Zero, IntPtr.Zero, null);
 
                         //Window doesn't exist anymore
@@ -461,11 +462,14 @@ namespace Avalonia.Win32
                 case WindowsMessage.WM_GETOBJECT:
                     if ((long)lParam == UiaRootObjectId)
                     {
-                        var provider = GetOrCreateAutomationProvider();
+                        if (_automationNode is null && AutomationStarted is object)
+                        {
+                            _automationNode = new RootAutomationNode(AutomationStarted);
+                        }
 
-                        if (provider is object)
+                        if (_automationNode is object)
                         {
-                            var r = UiaCoreProviderApi.UiaReturnRawElementProvider(_hwnd, wParam, lParam, provider);
+                            var r = UiaCoreProviderApi.UiaReturnRawElementProvider(_hwnd, wParam, lParam, _automationNode);
                             return r;
                         }
                     }

src/Windows/Avalonia.Win32/WindowImpl.cs

@@ -87,7 +87,7 @@ namespace Avalonia.Win32
         private POINT _maxTrackSize;
         private WindowImpl _parent;        
         private ExtendClientAreaChromeHints _extendChromeHints = ExtendClientAreaChromeHints.Default;
-        private AutomationNode _automationProvider;
+        private AutomationNode _automationNode;
         private bool _isCloseRequested;
         private bool _shown;
 
@@ -175,6 +175,7 @@ namespace Avalonia.Win32
         public Action LostFocus { get; set; }
 
         public Action<WindowTransparencyLevel> TransparencyLevelChanged { get; set; }
+        public Func<IAutomationNode, AutomationPeer> AutomationStarted { get; set; }
 
         public Thickness BorderThickness
         {
@@ -1269,17 +1270,6 @@ namespace Avalonia.Win32
         /// <inheritdoc/>
         public AcrylicPlatformCompensationLevels AcrylicCompensationLevels { get; } = new AcrylicPlatformCompensationLevels(1, 0.8, 0);
 
-        internal AutomationNode GetOrCreateAutomationProvider()
-        {
-            if (_automationProvider is null)
-            {
-                var peer = ControlAutomationPeer.GetOrCreatePeer(AutomationNodeFactory.Instance, (Control)_owner);
-                _automationProvider = peer.Node as AutomationNode;
-            }
-
-            return _automationProvider;
-        }
-
         private struct SavedWindowInfo
         {
             public WindowStyles Style { get; set; }