Added IEmbeddedRootProvider.

For some reason, on win32 embedded `IRawElementProviderFragmentRoot`s just don't show up, so we need an interface to distinguish between "actual" root peers and "embedded" root peers. Ideally `IRootProvider` and `IEmbeddedRootProvider` would share a common interface but that would be a breaking change.

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

@@ -39,7 +39,7 @@ namespace Avalonia.Automation.Peers
 
             var peer = GetOrCreate(hit);
 
-            while (peer != this && peer.GetProvider<IRootProvider>() is { } embedded)
+            while (peer != this && peer.GetProvider<IEmbeddedRootProvider>() is { } embedded)
             {
                 var embeddedHit = embedded.GetPeerFromPoint(p);
                 if (embeddedHit is null)

src/Avalonia.Controls/Automation/Provider/IEmbeddedRootProvider.cs

@@ -0,0 +1,33 @@
+using System;
+using Avalonia.Automation.Peers;
+
+namespace Avalonia.Automation.Provider
+{
+    /// <summary>
+    /// Exposure methods and properties to support UI Automation client access to the root of an
+    /// automation tree hosted by another UI framework.
+    /// </summary>
+    /// <remarks>
+    /// This interface is implemented by the <see cref="AutomationPeer"/> class, and can be used
+    /// to embed an automation tree from a 3rd party UI framework that wishes to use Avalonia's
+    /// automation support.
+    /// </remarks>
+    public interface IEmbeddedRootProvider
+    {
+        /// <summary>
+        /// Gets the currently focused element.
+        /// </summary>
+        AutomationPeer? GetFocus();
+
+        /// <summary>
+        /// Gets the element at the specified point, expressed in top-level coordinates.
+        /// </summary>
+        /// <param name="p">The point.</param>
+        AutomationPeer? GetPeerFromPoint(Point p);
+
+        /// <summary>
+        /// Raised by the automation peer when the focus changes.
+        /// </summary>
+        event EventHandler? FocusChanged;
+    }
+}

src/Avalonia.Controls/Automation/Provider/IRootProvider.cs

@@ -4,11 +4,36 @@ using Avalonia.Platform;
 
 namespace Avalonia.Automation.Provider
 {
+    /// <summary>
+    /// Exposes methods and properties to support UI Automation client access to the root of an
+    /// automation tree.
+    /// </summary>
+    /// <remarks>
+    /// This interface is implemented by the <see cref="AutomationPeer"/> class, and should only
+    /// be implemented on true root elements, such as Windows. To embed an automation tree, use
+    /// <see cref="IEmbeddedRootProvider"/> instead.
+    /// </remarks>
     public interface IRootProvider
     {
+        /// <summary>
+        /// Gets the platform implementation of the TopLevel for the element.
+        /// </summary>
         ITopLevelImpl? PlatformImpl { get; }
+
+        /// <summary>
+        /// Gets the currently focused element.
+        /// </summary>
         AutomationPeer? GetFocus();
+
+        /// <summary>
+        /// Gets the element at the specified point, expressed in top-level coordinates.
+        /// </summary>
+        /// <param name="p">The point.</param>
         AutomationPeer? GetPeerFromPoint(Point p);
+
+        /// <summary>
+        /// Raised by the automation peer when the focus changes.
+        /// </summary>
         event EventHandler? FocusChanged;
     }
 }

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

@@ -54,25 +54,11 @@ namespace Avalonia.Win32.Automation
             _runtimeId = new int[] { 3, GetHashCode() };
             Peer = peer;
             s_nodes.Add(peer, this);
-            peer.ChildrenChanged += Peer_ChildrenChanged;
-            peer.PropertyChanged += Peer_PropertyChanged;
-        }
-
-        private void Peer_ChildrenChanged(object? sender, EventArgs e)
-        {
-            ChildrenChanged();
-        }
+            peer.ChildrenChanged += OnPeerChildrenChanged;
+            peer.PropertyChanged += OnPeerPropertyChanged;
 
-        private void Peer_PropertyChanged(object? sender, AutomationPropertyChangedEventArgs e)
-        {
-            if (s_propertyMap.TryGetValue(e.Property, out var id))
-            {
-                UiaCoreProviderApi.UiaRaiseAutomationPropertyChangedEvent(
-                    this,
-                    (int)id,
-                    e.OldValue as IConvertible,
-                    e.NewValue as IConvertible);
-            }
+            if (Peer.GetProvider<AAP.IEmbeddedRootProvider>() is { } embeddedRoot)
+                embeddedRoot.FocusChanged += OnEmbeddedRootFocusChanged;
         }
 
         public AutomationPeer Peer { get; protected set; }
@@ -95,15 +81,6 @@ namespace Avalonia.Win32.Automation
         public virtual IRawElementProviderSimple? HostRawElementProvider => null;
         public ProviderOptions ProviderOptions => ProviderOptions.ServerSideProvider;
 
-        public void ChildrenChanged()
-        {
-            UiaCoreProviderApi.UiaRaiseStructureChangedEvent(
-                this,
-                StructureChangeType.ChildrenInvalidated,
-                null,
-                0);
-        }
-
         [return: MarshalAs(UnmanagedType.IUnknown)]
         public virtual object? GetPatternProvider(int patternId)
         {
@@ -250,6 +227,21 @@ namespace Avalonia.Win32.Automation
             throw new NotSupportedException();
         }
 
+        protected void RaiseChildrenChanged()
+        {
+            UiaCoreProviderApi.UiaRaiseStructureChangedEvent(
+                this,
+                StructureChangeType.ChildrenInvalidated,
+                null,
+                0);
+        }
+
+        protected void RaiseFocusChanged(AutomationNode? focused)
+        {
+            UiaCoreProviderApi.UiaRaiseAutomationEvent(
+                focused,
+                (int)UiaEventId.AutomationFocusChanged);
+        }
 
         private AutomationNode? GetRoot()
         {
@@ -267,6 +259,29 @@ namespace Avalonia.Win32.Automation
             return peer is object ? GetOrCreate(peer) : null;
         }
 
+        private void OnPeerChildrenChanged(object? sender, EventArgs e)
+        {
+            RaiseChildrenChanged();
+        }
+
+        private void OnPeerPropertyChanged(object? sender, AutomationPropertyChangedEventArgs e)
+        {
+            if (s_propertyMap.TryGetValue(e.Property, out var id))
+            {
+                UiaCoreProviderApi.UiaRaiseAutomationPropertyChangedEvent(
+                    this,
+                    (int)id,
+                    e.OldValue as IConvertible,
+                    e.NewValue as IConvertible);
+            }
+        }
+
+        private void OnEmbeddedRootFocusChanged(object? sender, EventArgs e)
+        {
+            if (Peer.GetProvider<AAP.IEmbeddedRootProvider>() is { } embeddedRoot)
+                RaiseFocusChanged(GetOrCreate(embeddedRoot.GetFocus()));
+        }
+
         private static AutomationNode Create(AutomationPeer peer)
         {
             return peer.GetProvider<AAP.IRootProvider>() is object ?

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

@@ -9,18 +9,14 @@ using Avalonia.Win32.Interop.Automation;
 namespace Avalonia.Win32.Automation
 {
     [RequiresUnreferencedCode("Requires .NET COM interop")]
-    internal class RootAutomationNode : AutomationNode,
-        IRawElementProviderFragmentRoot,
-        IRawElementProviderAdviseEvents
+    internal class RootAutomationNode : AutomationNode, IRawElementProviderFragmentRoot
     {
-        private int _raiseFocusChanged;
-
         public RootAutomationNode(AutomationPeer peer)
             : base(peer)
         {
             Peer = base.Peer.GetProvider<IRootProvider>() ?? throw new AvaloniaInternalException(
                 "Attempt to create RootAutomationNode from peer which does not implement IRootProvider.");
-            Peer.FocusChanged += FocusChanged;
+            Peer.FocusChanged += OnRootFocusChanged;
         }
 
         public override IRawElementProviderFragmentRoot? FragmentRoot => this;
@@ -44,41 +40,6 @@ namespace Avalonia.Win32.Automation
             return GetOrCreate(focus);
         }
 
-        void IRawElementProviderAdviseEvents.AdviseEventAdded(int eventId, int[] properties)
-        {
-            switch ((UiaEventId)eventId)
-            {
-                case UiaEventId.AutomationFocusChanged:
-                    ++_raiseFocusChanged;
-                    break;
-            }
-        }
-
-        void IRawElementProviderAdviseEvents.AdviseEventRemoved(int eventId, int[] properties)
-        {
-            switch ((UiaEventId)eventId)
-            {
-                case UiaEventId.AutomationFocusChanged:
-                    --_raiseFocusChanged;
-                    break;
-            }
-        }
-
-        protected void RaiseFocusChanged(AutomationNode? focused)
-        {
-            if (_raiseFocusChanged > 0)
-            {
-                UiaCoreProviderApi.UiaRaiseAutomationEvent(
-                    focused,
-                    (int)UiaEventId.AutomationFocusChanged);
-            }
-        }
-
-        public void FocusChanged(object? sender, EventArgs e)
-        {
-            RaiseFocusChanged(GetOrCreate(Peer.GetFocus()));
-        }
-
         public Rect ToScreen(Rect rect)
         {
             if (WindowImpl is null)
@@ -101,5 +62,10 @@ namespace Avalonia.Win32.Automation
                 return result;
             }
         }
+
+        private void OnRootFocusChanged(object? sender, EventArgs e)
+        {
+            RaiseFocusChanged(GetOrCreate(Peer.GetFocus()));
+        }
     }
 }