Add support for Flyouts, ToolTips & ContextMenus

src/Avalonia.Controls/Diagnostics/IPopupHostProvider.cs

@@ -0,0 +1,23 @@
+using System;
+using Avalonia.Controls.Primitives;
+
+#nullable enable
+
+namespace Avalonia.Controls.Diagnostics
+{
+    /// <summary>
+    /// Diagnostics interface to retrieve an associated <see cref="IPopupHost"/>.
+    /// </summary>
+    public interface IPopupHostProvider
+    {
+        /// <summary>
+        /// The popup host.
+        /// </summary>
+        IPopupHost? PopupHost { get; }
+
+        /// <summary>
+        /// Raised when the popup host changes.
+        /// </summary>
+        event Action<IPopupHost?>? PopupHostChanged;
+    }
+}

src/Avalonia.Controls/Diagnostics/ToolTipDiagnostics.cs

@@ -0,0 +1,12 @@
+#nullable enable
+
+namespace Avalonia.Controls.Diagnostics
+{
+    /// <summary>
+    /// Helper class to provide some diagnostics insides into <see cref="ToolTip"/>.
+    /// </summary>
+    public static class ToolTipDiagnostics
+    {
+        public static AvaloniaProperty<ToolTip?> ToolTipProperty = ToolTip.ToolTipProperty;
+    }
+}

src/Avalonia.Controls/Flyouts/FlyoutBase.cs

@@ -1,16 +1,16 @@
 using System;
 using System.ComponentModel;
+using Avalonia.Controls.Diagnostics;
 using Avalonia.Input;
 using Avalonia.Input.Raw;
 using Avalonia.Layout;
 using Avalonia.Logging;
-using Avalonia.Rendering;
 
 #nullable enable
 
 namespace Avalonia.Controls.Primitives
 {
-    public abstract class FlyoutBase : AvaloniaObject
+    public abstract class FlyoutBase : AvaloniaObject, IPopupHostProvider
     {
         static FlyoutBase()
         {
@@ -55,6 +55,7 @@ namespace Avalonia.Controls.Primitives
         private Rect? _enlargedPopupRect;
         private PixelRect? _enlargePopupRectScreenPixelRect;
         private IDisposable? _transientDisposable;
+        private Action<IPopupHost?>? _popupHostChangedHandler;
 
         protected Popup? Popup { get; private set; }
 
@@ -94,6 +95,14 @@ namespace Avalonia.Controls.Primitives
             private set => SetAndRaise(TargetProperty, ref _target, value);
         }
 
+        IPopupHost? IPopupHostProvider.PopupHost => Popup?.Host;
+
+        event Action<IPopupHost?>? IPopupHostProvider.PopupHostChanged 
+        { 
+            add => _popupHostChangedHandler += value; 
+            remove => _popupHostChangedHandler -= value;
+        }
+
         public event EventHandler? Closed;
         public event EventHandler<CancelEventArgs>? Closing;
         public event EventHandler? Opened;
@@ -322,9 +331,11 @@ namespace Avalonia.Controls.Primitives
 
         private void InitPopup()
         {
-            Popup = new Popup();
-            Popup.WindowManagerAddShadowHint = false;
-            Popup.IsLightDismissEnabled = true;
+            Popup = new Popup
+            {
+                WindowManagerAddShadowHint = false,
+                IsLightDismissEnabled = true
+            };
 
             Popup.Opened += OnPopupOpened;
             Popup.Closed += OnPopupClosed;
@@ -333,11 +344,15 @@ namespace Avalonia.Controls.Primitives
         private void OnPopupOpened(object sender, EventArgs e)
         {
             IsOpen = true;
+
+            _popupHostChangedHandler?.Invoke(Popup!.Host);
         }
 
         private void OnPopupClosed(object sender, EventArgs e)
         {
             HideCore();
+
+            _popupHostChangedHandler?.Invoke(null);
         }
 
         private void PositionPopup(bool showAtPointer)

src/Avalonia.Controls/ToolTip.cs

@@ -1,9 +1,8 @@
 #nullable enable
 using System;
-using System.Reactive.Linq;
+using Avalonia.Controls.Diagnostics;
 using Avalonia.Controls.Metadata;
 using Avalonia.Controls.Primitives;
-using Avalonia.VisualTree;
 
 namespace Avalonia.Controls
 {
@@ -17,7 +16,7 @@ namespace Avalonia.Controls
     /// assigning the content that you want displayed.
     /// </remarks>
     [PseudoClasses(":open")]
-    public class ToolTip : ContentControl
+    public class ToolTip : ContentControl, IPopupHostProvider
     {
         /// <summary>
         /// Defines the ToolTip.Tip attached property.
@@ -61,7 +60,8 @@ namespace Avalonia.Controls
         internal static readonly AttachedProperty<ToolTip?> ToolTipProperty =
             AvaloniaProperty.RegisterAttached<ToolTip, Control, ToolTip?>("ToolTip");
 
-        private IPopupHost? _popup;
+        private IPopupHost? _popupHost;
+        private Action<IPopupHost?>? _popupHostChangedHandler;
 
         /// <summary>
         /// Initializes static members of the <see cref="ToolTip"/> class.
@@ -251,35 +251,45 @@ namespace Avalonia.Controls
 
             tooltip.RecalculatePosition(control);
         }
+        
+        IPopupHost? IPopupHostProvider.PopupHost => _popupHost;
+
+        event Action<IPopupHost?>? IPopupHostProvider.PopupHostChanged 
+        { 
+            add => _popupHostChangedHandler += value; 
+            remove => _popupHostChangedHandler -= value;
+        }
 
         internal void RecalculatePosition(Control control)
         {
-            _popup?.ConfigurePosition(control, GetPlacement(control), new Point(GetHorizontalOffset(control), GetVerticalOffset(control)));
+            _popupHost?.ConfigurePosition(control, GetPlacement(control), new Point(GetHorizontalOffset(control), GetVerticalOffset(control)));
         }
 
         private void Open(Control control)
         {
             Close();
 
-            _popup = OverlayPopupHost.CreatePopupHost(control, null);
-            _popup.SetChild(this);
-            ((ISetLogicalParent)_popup).SetParent(control);
+            _popupHost = OverlayPopupHost.CreatePopupHost(control, null);
+            _popupHost.SetChild(this);
+            ((ISetLogicalParent)_popupHost).SetParent(control);
             
-            _popup.ConfigurePosition(control, GetPlacement(control), 
+            _popupHost.ConfigurePosition(control, GetPlacement(control), 
                 new Point(GetHorizontalOffset(control), GetVerticalOffset(control)));
 
-            WindowManagerAddShadowHintChanged(_popup, false);
+            WindowManagerAddShadowHintChanged(_popupHost, false);
 
-            _popup.Show();
+            _popupHost.Show();
+            _popupHostChangedHandler?.Invoke(_popupHost);
         }
 
         private void Close()
         {
-            if (_popup != null)
+            if (_popupHost != null)
             {
-                _popup.SetChild(null);
-                _popup.Dispose();
-                _popup = null;
+                _popupHost.SetChild(null);
+                _popupHost.Dispose();
+                _popupHost = null;
+                _popupHostChangedHandler?.Invoke(null);
             }
         }
 

src/Avalonia.Diagnostics/Diagnostics/ViewModels/TreeNode.cs

@@ -4,6 +4,7 @@ using System.Collections.Specialized;
 using System.Reactive;
 using System.Reactive.Linq;
 using Avalonia.Controls;
+using Avalonia.Controls.Diagnostics;
 using Avalonia.Controls.Primitives;
 using Avalonia.LogicalTree;
 using Avalonia.Media;
@@ -19,12 +20,11 @@ namespace Avalonia.Diagnostics.ViewModels
 
         protected TreeNode(IVisual visual, TreeNode? parent)
         {
+            _classes = string.Empty;
             Parent = parent;
             Type = visual.GetType().Name;
             Visual = visual;
-            _classes = string.Empty;
-
-            FontWeight = Visual is TopLevel || Visual is Popup ? FontWeight.Bold : FontWeight.Normal;
+            FontWeight = IsRoot ? FontWeight.Bold : FontWeight.Normal;
 
             if (visual is IControl control)
             {
@@ -56,6 +56,11 @@ namespace Avalonia.Diagnostics.ViewModels
             }
         }
 
+        private bool IsRoot => Visual is TopLevel || 
+                               Visual is Popup ||
+                               Visual is ContextMenu ||
+                               Visual is IPopupHost;
+
         public FontWeight FontWeight { get; }
 
         public abstract TreeNodeCollection Children

src/Avalonia.Diagnostics/Diagnostics/ViewModels/VisualTreeNode.cs

@@ -1,5 +1,10 @@
 using System;
+using System.Reactive.Disposables;
+using System.Reactive.Linq;
+using System.Security.Cryptography.X509Certificates;
 using Avalonia.Collections;
+using Avalonia.Controls;
+using Avalonia.Controls.Diagnostics;
 using Avalonia.Controls.Primitives;
 using Avalonia.Styling;
 using Avalonia.VisualTree;
@@ -13,7 +18,7 @@ namespace Avalonia.Diagnostics.ViewModels
         {
             Children = new VisualTreeNodeCollection(this, visual);
 
-            if ((Visual is IStyleable styleable))
+            if (Visual is IStyleable styleable)
             {
                 IsInTemplate = styleable.TemplatedParent != null;
             }
@@ -25,13 +30,15 @@ namespace Avalonia.Diagnostics.ViewModels
 
         public static VisualTreeNode[] Create(object control)
         {
-            return control is IVisual visual ? new[] { new VisualTreeNode(visual, null) } : Array.Empty<VisualTreeNode>();
+            return control is IVisual visual ?
+                new[] { new VisualTreeNode(visual, null) } :
+                Array.Empty<VisualTreeNode>();
         }
 
         internal class VisualTreeNodeCollection : TreeNodeCollection
         {
             private readonly IVisual _control;
-            private IDisposable? _subscription;
+            private readonly CompositeDisposable _subscriptions = new CompositeDisposable(2);
 
             public VisualTreeNodeCollection(TreeNode owner, IVisual control)
                 : base(owner)
@@ -41,33 +48,79 @@ namespace Avalonia.Diagnostics.ViewModels
 
             public override void Dispose()
             {
-                _subscription?.Dispose();
+                _subscriptions.Dispose();
             }
 
-            protected override void Initialize(AvaloniaList<TreeNode> nodes)
+            private static IObservable<IControl?>? GetHostedPopupRootObservable(IVisual visual)
             {
-                if (_control is Popup p)
+                static IObservable<IControl?> GetPopupHostObservable(IPopupHostProvider popupHostProvider)
                 {
-                    _subscription = p.GetObservable(Popup.ChildProperty).Subscribe(child =>
-                    {
-                        if (child != null)
-                        {
-                            nodes.Add(new VisualTreeNode(child, Owner));
-                        }
-                        else
-                        {
-                            nodes.Clear();
-                        }
-
-                    });
+                    return Observable.FromEvent<IPopupHost?>(
+                            x => popupHostProvider.PopupHostChanged += x,
+                            x => popupHostProvider.PopupHostChanged -= x)
+                        .StartWith(popupHostProvider.PopupHost)
+                        .Select(x => x is IControl c ? c : null);
                 }
-                else
+
+                return visual switch
                 {
-                    _subscription = _control.VisualChildren.ForEachItem(
+                    Popup p => p.GetObservable(Popup.ChildProperty),
+                    Control c => Observable.CombineLatest(
+                            c.GetObservable(Control.ContextFlyoutProperty),
+                            c.GetObservable(Control.ContextMenuProperty),
+                            c.GetObservable(FlyoutBase.AttachedFlyoutProperty),
+                            c.GetObservable(ToolTipDiagnostics.ToolTipProperty),
+                            (ContextFlyout, ContextMenu, AttachedFlyout, ToolTip) =>
+                            {
+                                if (ContextMenu != null)
+                                {
+                                    //Note: ContextMenus are special since all the items are added as visual children.
+                                    //So we don't need to go via Popup
+                                    return Observable.Return<IControl?>(ContextMenu);
+                                }
+
+                                if ((ContextFlyout ?? (IPopupHostProvider?) AttachedFlyout ?? ToolTip) is { } popupHostProvider)
+                                {
+                                    return GetPopupHostObservable(popupHostProvider);
+                                }
+
+                                return Observable.Return<IControl?>(null);
+                            })
+                        .Switch(),
+                    _ => null
+                };
+            }
+
+            protected override void Initialize(AvaloniaList<TreeNode> nodes)
+            {
+                _subscriptions.Clear();
+
+                if (GetHostedPopupRootObservable(_control) is { } popupRootObservable)
+                {
+                    VisualTreeNode? childNode = null;
+
+                    _subscriptions.Add(
+                        popupRootObservable
+                            .Subscribe(root =>
+                            {
+                                if (root != null)
+                                {
+                                    childNode = new VisualTreeNode(root, Owner);
+
+                                    nodes.Add(childNode);
+                                }
+                                else if (childNode != null)
+                                {
+                                    nodes.Remove(childNode);
+                                }
+                            }));
+                }
+
+                _subscriptions.Add(
+                    _control.VisualChildren.ForEachItem(
                         (i, item) => nodes.Insert(i, new VisualTreeNode(item, Owner)),
                         (i, item) => nodes.RemoveAt(i),
-                        () => nodes.Clear());
-                }
+                        () => nodes.Clear()));
             }
         }
     }