Implement TopLevel.OpenedPopups (#22074)

* Implement TopLevel.OpenedPopups

* Delete Headless `GetOpenPopups`

* Reorganize popup tests between Headless/Primitives layers

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

* Add Popup.OpenedPopups to keep opened popups in tree structure

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

* Help NUnit suppressing CS8777

* Update suppresions

---------

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

api/Avalonia.Headless.nupkg.xml

@@ -0,0 +1,16 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- https://learn.microsoft.com/dotnet/fundamentals/package-validation/diagnostic-ids -->
+<Suppressions xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
+  <Suppression>
+    <DiagnosticId>CP0002</DiagnosticId>
+    <Target>M:Avalonia.Headless.HeadlessWindowExtensions.GetOpenPopups(Avalonia.Controls.TopLevel)</Target>
+    <Left>baseline/Avalonia.Headless/lib/net10.0/Avalonia.Headless.dll</Left>
+    <Right>current/Avalonia.Headless/lib/net10.0/Avalonia.Headless.dll</Right>
+  </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0002</DiagnosticId>
+    <Target>M:Avalonia.Headless.HeadlessWindowExtensions.GetOpenPopups(Avalonia.Controls.TopLevel)</Target>
+    <Left>baseline/Avalonia.Headless/lib/net8.0/Avalonia.Headless.dll</Left>
+    <Right>current/Avalonia.Headless/lib/net8.0/Avalonia.Headless.dll</Right>
+  </Suppression>
+</Suppressions>

src/Avalonia.Controls/Primitives/Popup.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using System.ComponentModel;
 using System.Diagnostics.CodeAnalysis;
 using Avalonia.Reactive;
@@ -153,6 +154,7 @@ namespace Avalonia.Controls.Primitives
         private bool _isUsingOverlayLayer;
         private PopupOpenState? _openState;
         private Action<IPopupHost?>? _popupHostChangedHandler;
+        private List<Popup>? _openedPopups;
 
         /// <summary>
         /// Initializes static members of the <see cref="Popup"/> class.
@@ -177,6 +179,11 @@ namespace Avalonia.Controls.Primitives
 
         internal IPopupHost? Host => _openState?.PopupHost;
 
+        /// <summary>
+        /// Gets the popups that are currently open directly inside this popup, in the order they were opened.
+        /// </summary>
+        public IReadOnlyList<Popup> OpenedPopups => _openedPopups ?? (IReadOnlyList<Popup>)[];
+
         /// <summary>
         /// Gets or sets a hint to the window manager that a shadow should be added to the popup.
         /// </summary>
@@ -575,7 +582,12 @@ namespace Avalonia.Controls.Primitives
                 }
             }
 
-            _openState = new PopupOpenState(placementTarget, topLevel, popupHost, cleanupPopup);
+            _openState = new PopupOpenState(placementTarget, topLevel, popupHost, cleanupPopup, FindParentPopup(placementTarget));
+
+            if (_openState.ParentPopup is { } parentPopup)
+                parentPopup.AddOpenedPopup(this);
+            else
+                topLevel.AddOpenedPopup(this);
 
             WindowManagerAddShadowHintChanged(popupHost, WindowManagerAddShadowHint);
 
@@ -844,6 +856,11 @@ namespace Avalonia.Controls.Primitives
                 return;
             }
 
+            if (_openState.ParentPopup is { } parentPopup)
+                parentPopup.RemoveOpenedPopup(this);
+            else
+                _openState.TopLevel.RemoveOpenedPopup(this);
+
             _openState.Dispose();
             _openState = null;
 
@@ -1063,22 +1080,41 @@ namespace Avalonia.Controls.Primitives
             }
         }
 
+        internal void AddOpenedPopup(Popup popup) => (_openedPopups ??= new List<Popup>(capacity: 2)).Add(popup);
+
+        internal void RemoveOpenedPopup(Popup popup) => _openedPopups?.Remove(popup);
+
+        private static Popup? FindParentPopup(Visual placementTarget)
+        {
+            foreach (var visual in placementTarget.GetSelfAndVisualAncestors())
+            {
+                if (visual is IPopupHost)
+                    return (visual as StyledElement)?.Parent as Popup;
+            }
+
+            return null;
+        }
+
         private class PopupOpenState : IDisposable
         {
             private readonly IDisposable _cleanup;
             private IDisposable? _presenterCleanup;
             private Control _placementTarget;
 
-            public PopupOpenState(Control placementTarget, TopLevel topLevel, IPopupHost popupHost, IDisposable cleanup)
+            public PopupOpenState(Control placementTarget, TopLevel topLevel, IPopupHost popupHost, IDisposable cleanup,
+                Popup? parentPopup)
             {
                 PlacementTarget = placementTarget;
                 TopLevel = topLevel;
+                ParentPopup = parentPopup;
                 PopupHost = popupHost;
                 _cleanup = cleanup;
             }
 
             public TopLevel TopLevel { get; }
 
+            public Popup? ParentPopup { get; }
+
             public Control PlacementTarget
             {
                 get => _placementTarget;

src/Avalonia.Controls/Primitives/PopupRoot.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using Avalonia.Automation.Peers;
 using Avalonia.Controls.Primitives.PopupPositioning;
 using Avalonia.Diagnostics;
@@ -122,6 +123,8 @@ namespace Avalonia.Controls.Primitives
 
         public TopLevel ParentTopLevel { get; }
 
+        public override IReadOnlyList<Popup> OpenedPopups => (Parent as Popup)?.OpenedPopups ?? [];
+
         /// <inheritdoc/>
         public void Dispose()
         {

src/Avalonia.Controls/TopLevel.cs

@@ -132,6 +132,7 @@ namespace Avalonia.Controls
         private TargetWeakEventSubscriber<TopLevel, ResourcesChangedEventArgs>? _resourcesChangesSubscriber;
         private IStorageProvider? _storageProvider;
         private Screens? _screens;
+        private List<Popup>? _openedPopups;
         private readonly PresentationSource _source;
         private readonly TopLevelHost _topLevelHost;
         internal TopLevelHost TopLevelHost => _topLevelHost;
@@ -559,6 +560,14 @@ namespace Avalonia.Controls
         // TODO: Un-private
         private IPlatformSettings? PlatformSettings => AvaloniaLocator.Current.GetService<IPlatformSettings>();
 
+        /// <summary>
+        /// Gets the popups that are currently open directly in this top level, in the order they were opened.
+        /// </summary>
+        /// <remarks>
+        /// Use <see cref="Popup.OpenedPopups"/> for nested popups.
+        /// </remarks>
+        public virtual IReadOnlyList<Popup> OpenedPopups => _openedPopups ?? (IReadOnlyList<Popup>)[];
+
         /// <summary>
         /// Gets the <see cref="TopLevel" /> for which the given <see cref="Visual"/> is hosted in.
         /// </summary>
@@ -708,6 +717,7 @@ namespace Avalonia.Controls
 
             LayoutManager.Dispose();
             _platformImplBindings.Clear();
+            _openedPopups = null;
         }
 
         /// <summary>
@@ -724,6 +734,10 @@ namespace Avalonia.Controls
             Renderer.Resized(clientSize);
         }
 
+        internal void AddOpenedPopup(Popup popup) => (_openedPopups ??= new List<Popup>(capacity: 2)).Add(popup);
+
+        internal void RemoveOpenedPopup(Popup popup) => _openedPopups?.Remove(popup);
+
         /// <summary>
         /// Handles a window scaling change notification from 
         /// <see cref="ITopLevelImpl.ScalingChanged"/>.

src/Headless/Avalonia.Headless/AvaloniaHeadlessPlatform.cs

@@ -121,8 +121,6 @@ namespace Avalonia.Headless
 
         /// <summary>
         /// Embeds popups to the window when set to true. The default value is true.
-        /// When disabled, popups are hosted in dedicated headless top-levels that are not part of
-        /// the parent's visual tree; use <see cref="HeadlessWindowExtensions.GetOpenPopups"/> to access them.
         /// </summary>
         // TODO13: Change the default to false to match the other desktop platforms.
         public bool OverlayPopups { get; set; } = true;

src/Headless/Avalonia.Headless/HeadlessWindowExtensions.cs

@@ -115,18 +115,6 @@ public static class HeadlessWindowExtensions
         DragDropEffects effects, RawInputModifiers modifiers = RawInputModifiers.None) =>
         RunJobsOnImpl(topLevel, w => w.DragDrop(point, type, data, effects, modifiers));
 
-    /// <summary>
-    /// Returns the popups currently open directly above this toplevel, in z-order (bottom to top).
-    /// For popups nested in another popup, call this method on that popup's toplevel.
-    /// </summary>
-    /// <remarks>
-    /// Only popups hosted in dedicated headless top-levels are returned, which requires disabling
-    /// <see cref="AvaloniaHeadlessPlatformOptions.OverlayPopups"/>. Popups hosted in the overlay
-    /// layer are part of the parent's visual tree and are not tracked by the platform.
-    /// </remarks>
-    public static IReadOnlyList<TopLevel> GetOpenPopups(this TopLevel topLevel) =>
-        GetImpl(topLevel).GetOpenPopups();
-
     /// <summary>
     /// Changes the render scaling (DPI) of the headless window/toplevel.
     /// This simulates a DPI change, triggering scaling changed notifications and a layout pass.

src/Headless/Avalonia.Headless/HeadlessWindowImpl.cs

@@ -27,7 +27,6 @@ namespace Avalonia.Headless
         private readonly AvaloniaHeadlessPlatformOptions _options;
         private readonly HeadlessWindowImpl? _popupParent;
         private readonly IPopupPositioner? _popupPositioner;
-        private readonly List<HeadlessWindowImpl> _openPopups = new();
         public bool IsPopup { get; }
 
         public HeadlessWindowImpl(AvaloniaHeadlessPlatformOptions options)
@@ -60,7 +59,6 @@ namespace Avalonia.Headless
 
         public void Dispose()
         {
-            _popupParent?._openPopups.Remove(this);
             Closed?.Invoke();
             _lastRenderedFrame?.Dispose();
             _lastRenderedFrame = null;
@@ -101,9 +99,6 @@ namespace Avalonia.Headless
 
         public void Show(bool activate, bool isDialog)
         {
-            if (_popupParent != null && !_popupParent._openPopups.Contains(this))
-                _popupParent._openPopups.Add(this);
-
             if (activate)
             {
                 ZOrder = _nextGlobalZOrder++;
@@ -113,7 +108,6 @@ namespace Avalonia.Headless
 
         public void Hide()
         {
-            _popupParent?._openPopups.Remove(this);
             Dispatcher.UIThread.Post(() => Deactivated?.Invoke(), DispatcherPriority.Input);
         }
 
@@ -403,21 +397,6 @@ namespace Avalonia.Headless
 
         public IPopupImpl? CreatePopup() => _options.OverlayPopups ? null : new HeadlessWindowImpl(this);
 
-        public IReadOnlyList<TopLevel> GetOpenPopups()
-        {
-            if (_openPopups.Count == 0)
-                return Array.Empty<TopLevel>();
-
-            var result = new List<TopLevel>(_openPopups.Count);
-            foreach (var popup in _openPopups)
-            {
-                if (popup.InputRoot is PresentationSource { FocusRoot: TopLevel topLevel })
-                    result.Add(topLevel);
-            }
-
-            return result;
-        }
-
         public void SetWindowManagerAddShadowHint(bool enabled)
         {
             

src/Headless/Avalonia.Headless/IHeadlessWindow.cs

@@ -19,6 +19,5 @@ namespace Avalonia.Headless
         void MouseWheel(Point point, Vector delta, RawInputModifiers modifiers = RawInputModifiers.None);
         void DragDrop(Point point, RawDragEventType type, IDataTransfer data, DragDropEffects effects, RawInputModifiers modifiers = RawInputModifiers.None);
         void SetRenderScaling(double scaling);
-        IReadOnlyList<TopLevel> GetOpenPopups();
     }
 }

tests/Avalonia.Controls.UnitTests/Primitives/PopupTests.cs

@@ -1392,6 +1392,109 @@ namespace Avalonia.Controls.UnitTests.Primitives
             }
         }
 
+        [Fact]
+        public void Opened_Popup_Should_Be_In_OpenedPopups()
+        {
+            using (CreateServices())
+            {
+                var target = new Popup();
+                var window = PreparedWindow(target);
+
+                target.Open();
+
+                Assert.Equal(new[] { target }, window.OpenedPopups);
+
+                target.Close();
+
+                Assert.Empty(window.OpenedPopups);
+            }
+        }
+
+        [Fact]
+        public void Closing_Popup_With_IsOpen_Should_Remove_It_From_OpenedPopups()
+        {
+            using (CreateServices())
+            {
+                var target = new Popup();
+                var window = PreparedWindow(target);
+
+                target.IsOpen = true;
+
+                Assert.Equal(new[] { target }, window.OpenedPopups);
+
+                target.IsOpen = false;
+
+                Assert.Empty(window.OpenedPopups);
+            }
+        }
+
+        [Fact]
+        public void Closing_Window_Should_Clear_OpenedPopups()
+        {
+            using (CreateServices())
+            {
+                var target = new Popup();
+                var window = PreparedWindow(target);
+
+                target.Open();
+                window.Close();
+
+                Assert.Empty(window.OpenedPopups);
+            }
+        }
+
+        [Fact]
+        public void Nested_Popup_Should_Be_In_Parent_Popup_OpenedPopups()
+        {
+            using (CreateServices())
+            {
+                var nestedTarget = new Border { Width = 20, Height = 20 };
+                var nestedPopup = new Popup
+                {
+                    PlacementTarget = nestedTarget,
+                    Child = new Border { Width = 10, Height = 10 }
+                };
+                var target = new Border();
+                var popup = new Popup
+                {
+                    PlacementTarget = target,
+                    Child = new Panel { Children = { nestedTarget, nestedPopup } }
+                };
+                var window = PreparedWindow(new Panel { Children = { target, popup } });
+
+                popup.Open();
+
+                if (popup.Host is OverlayPopupHost host)
+                {
+                    //Need to measure/arrange for visual children to show up
+                    //in OverlayPopupHost
+                    host.Measure(Size.Infinity);
+                    host.Arrange(new Rect(host.DesiredSize));
+                }
+
+                nestedPopup.Open();
+
+                Assert.Equal([popup], window.OpenedPopups);
+                Assert.Equal([nestedPopup], popup.OpenedPopups);
+                Assert.Empty(nestedPopup.OpenedPopups);
+
+                if (popup.Host is PopupRoot popupRoot)
+                {
+                    // A popup root exposes the popups opened by its own popup.
+                    Assert.Equal([nestedPopup], popupRoot.OpenedPopups);
+                }
+
+                nestedPopup.Close();
+
+                Assert.Equal([popup], window.OpenedPopups);
+                Assert.Empty(popup.OpenedPopups);
+
+                popup.Close();
+
+                Assert.Empty(window.OpenedPopups);
+            }
+        }
+
         private IDisposable CreateServices()
         {
             return UnitTestApplication.Start(TestServices.StyledWindow.With(
@@ -1430,13 +1533,22 @@ namespace Avalonia.Controls.UnitTests.Primitives
                 {
                     if (UsePopupHost)
                         return null;
-                    return MockWindowingPlatform.CreatePopupMock(mock.Object).Object;
+                    return CreatePopupMock(mock.Object);
                 });
 
                 return mock.Object;
             }, null);
         }
 
+        private static IPopupImpl CreatePopupMock(IWindowBaseImpl parent)
+        {
+            var mock = MockWindowingPlatform.CreatePopupMock(parent);
+
+            mock.Setup(x => x.CreatePopup()).Returns(() => CreatePopupMock(mock.Object));
+
+            return mock.Object;
+        }
+
         private static Window PreparedWindow(object? content = null)
         {
             var w = new Window { Content = content };

tests/Avalonia.Headless.UnitTests/AssertHelper.cs

@@ -1,5 +1,7 @@
 #nullable enable
 
+using System.Diagnostics.CodeAnalysis;
+
 namespace Avalonia.Headless.UnitTests;
 
 internal static class AssertHelper
@@ -22,14 +24,26 @@ internal static class AssertHelper
 #endif
     }
 
-    public static void NotNull(object? value)
+    public static void Null(object? value)
+    {
+#if NUNIT
+        Assert.That(value, Is.Null);
+#elif XUNIT
+        Assert.Null(value);
+#endif
+    }
+
+    public static void NotNull([NotNull] object? value)
     {
 #if NUNIT
         Assert.That(value, Is.Not.Null);
 #elif XUNIT
         Assert.NotNull(value);
 #endif
+        // NUnit doesn't suppress CS8777 warning on its own
+#pragma warning disable CS8777 // Parameter must have a non-null value when exiting.
     }
+#pragma warning restore CS8777 // Parameter must have a non-null value when exiting.
 
     public static void Equal<T>(T expected, T actual)
     {

tests/Avalonia.Headless.UnitTests/MouseDeviceTests.cs

@@ -65,7 +65,11 @@ public class MouseDeviceTests
 
         // Pressing captures the pointer implicitly on the window's border.
         window.MouseDown(new Point(50, 50), MouseButton.Left);
-        window.GetOpenPopups()[0].MouseMove(new Point(40, 15));
+
+        var popupRoot = PopupTests.GetPopupTopLevel(popup);
+        AssertHelper.NotNull(popupRoot);
+
+        popupRoot.MouseMove(new Point(40, 15));
 
         AssertHelper.Same(TestApplication.UsesSharedMouseDevice ? target : popupChild, moveTarget);
 

tests/Avalonia.Headless.UnitTests/PopupTests.cs

@@ -32,7 +32,7 @@ public class PopupTests
 #elif XUNIT
     [AvaloniaFact]
 #endif
-    public void Popup_Uses_Dedicated_TopLevel_And_Is_Discoverable()
+    public void Popup_Uses_Dedicated_TopLevel()
     {
         var target = new Border { Background = Brushes.Red };
         var popup = new Popup
@@ -49,22 +49,22 @@ public class PopupTests
         window.Show();
         Dispatcher.UIThread.RunJobs();
 
-        AssertHelper.Equal(0, window.GetOpenPopups().Count);
+        AssertHelper.False(popup.IsOpen);
+        AssertHelper.False(popup.IsUsingOverlayLayer);
+        AssertHelper.Null(GetPopupTopLevel(popup));
 
         popup.Open();
         Dispatcher.UIThread.RunJobs();
 
         AssertHelper.True(popup.IsOpen);
         AssertHelper.False(popup.IsUsingOverlayLayer);
-        AssertHelper.Equal(1, window.GetOpenPopups().Count);
-        AssertHelper.True(window.GetOpenPopups()[0] is PopupRoot);
-
-        popup.Close();
-        Dispatcher.UIThread.RunJobs();
-
-        AssertHelper.Equal(0, window.GetOpenPopups().Count);
+        AssertHelper.True(GetPopupTopLevel(popup) is PopupRoot);
 
         window.Close();
+
+        AssertHelper.False(popup.IsOpen);
+        AssertHelper.False(popup.IsUsingOverlayLayer);
+        AssertHelper.Null(GetPopupTopLevel(popup));
     }
 
 #if NUNIT
@@ -72,31 +72,40 @@ public class PopupTests
 #elif XUNIT
     [AvaloniaFact]
 #endif
-    public void Can_Click_Button_Inside_Platform_Popup()
+    public void Popup_Placement_Respects_Window_Position()
     {
-        var clickCount = 0;
-        var button = new Button { Width = 80, Height = 30 };
-        button.Click += (_, _) => clickCount++;
-
-        var target = new Border { Background = Brushes.Red };
-        var popup = new Popup { PlacementTarget = target, Child = button };
+        var target = new Border
+        {
+            Width = 20,
+            Height = 20,
+            HorizontalAlignment = HorizontalAlignment.Left,
+            VerticalAlignment = VerticalAlignment.Top,
+            Background = Brushes.Red
+        };
+        var popup = new Popup
+        {
+            PlacementTarget = target,
+            Placement = PlacementMode.Bottom,
+            Child = new Border { Width = 20, Height = 20 }
+        };
         var window = new Window
         {
             Width = 100,
             Height = 100,
             Content = new Panel { Children = { target, popup } }
         };
+        window.Position = new PixelPoint(100, 200);
         window.Show();
         Dispatcher.UIThread.RunJobs();
 
         popup.Open();
         Dispatcher.UIThread.RunJobs();
 
-        var popupRoot = window.GetOpenPopups()[0];
-        popupRoot.MouseDown(new Point(40, 15), MouseButton.Left);
-        popupRoot.MouseUp(new Point(40, 15), MouseButton.Left);
+        var popupRoot = GetPopupTopLevel(popup);
+        AssertHelper.NotNull(popupRoot);
 
-        AssertHelper.Equal(1, clickCount);
+        var expected = target.PointToScreen(new Point(0, target.Bounds.Height));
+        AssertHelper.Equal(expected, popupRoot.PointToScreen(default));
 
         window.Close();
     }
@@ -106,38 +115,33 @@ public class PopupTests
 #elif XUNIT
     [AvaloniaFact]
 #endif
-    public void Popup_Placement_Respects_Window_Position()
+    public void Can_Click_Button_Inside_Platform_Popup()
     {
-        var target = new Border
-        {
-            Width = 20,
-            Height = 20,
-            HorizontalAlignment = HorizontalAlignment.Left,
-            VerticalAlignment = VerticalAlignment.Top,
-            Background = Brushes.Red
-        };
-        var popup = new Popup
-        {
-            PlacementTarget = target,
-            Placement = PlacementMode.Bottom,
-            Child = new Border { Width = 20, Height = 20 }
-        };
+        var clickCount = 0;
+        var button = new Button { Width = 80, Height = 30 };
+        button.Click += (_, _) => clickCount++;
+
+        var target = new Border { Background = Brushes.Red };
+        var popup = new Popup { PlacementTarget = target, Child = button };
         var window = new Window
         {
             Width = 100,
             Height = 100,
             Content = new Panel { Children = { target, popup } }
         };
-        window.Position = new PixelPoint(100, 200);
         window.Show();
         Dispatcher.UIThread.RunJobs();
 
         popup.Open();
         Dispatcher.UIThread.RunJobs();
 
-        var popupRoot = window.GetOpenPopups()[0];
-        var expected = target.PointToScreen(new Point(0, target.Bounds.Height));
-        AssertHelper.Equal(expected, popupRoot.PointToScreen(default));
+        var popupRoot = GetPopupTopLevel(popup);
+        AssertHelper.NotNull(popupRoot);
+
+        popupRoot.MouseDown(new Point(40, 15), MouseButton.Left);
+        popupRoot.MouseUp(new Point(40, 15), MouseButton.Left);
+
+        AssertHelper.Equal(1, clickCount);
 
         window.Close();
     }
@@ -147,7 +151,7 @@ public class PopupTests
 #elif XUNIT
     [AvaloniaFact]
 #endif
-    public void Nested_Popup_Is_Child_Of_Popup_Root()
+    public void Nested_Popup_Is_Owned_By_Parent_Popup()
     {
         var nestedTarget = new Border { Width = 20, Height = 20, Background = Brushes.Green };
         var nestedPopup = new Popup
@@ -175,11 +179,34 @@ public class PopupTests
         nestedPopup.Open();
         Dispatcher.UIThread.RunJobs();
 
-        var popupRoot = window.GetOpenPopups()[0];
-        AssertHelper.Equal(1, window.GetOpenPopups().Count);
-        AssertHelper.Equal(1, popupRoot.GetOpenPopups().Count);
-        AssertHelper.True(popupRoot.GetOpenPopups()[0] is PopupRoot);
+        AssertHelper.Equal(1, window.OpenedPopups.Count);
+        AssertHelper.Same(popup, window.OpenedPopups[0]);
+
+        AssertHelper.Equal(1, popup.OpenedPopups.Count);
+        AssertHelper.Same(nestedPopup, popup.OpenedPopups[0]);
+        AssertHelper.Equal(0, nestedPopup.OpenedPopups.Count);
+
+        // The nested popup is hosted in the parent popup's own top level.
+        AssertHelper.Same(GetPopupTopLevel(popup), TopLevel.GetTopLevel(nestedTarget));
+
+        nestedPopup.Close();
+        Dispatcher.UIThread.RunJobs();
+
+        AssertHelper.Equal(0, popup.OpenedPopups.Count);
+        AssertHelper.Equal(1, window.OpenedPopups.Count);
+
+        popup.Close();
+        Dispatcher.UIThread.RunJobs();
+
+        AssertHelper.Equal(0, window.OpenedPopups.Count);
 
         window.Close();
     }
+
+    internal static TopLevel GetPopupTopLevel(Popup popup)
+    {
+        AssertHelper.NotNull(popup.Child);
+        var topLevel = TopLevel.GetTopLevel(popup.Child);
+        return topLevel;
+    }
 }

tests/Avalonia.UnitTests/MockWindowingPlatform.cs

@@ -101,6 +101,7 @@ namespace Avalonia.UnitTests
             popupImpl.Setup(x => x.Compositor).Returns(compositor);
             popupImpl.Setup(x => x.ClientSize).Returns(() => clientSize);
             popupImpl.Setup(x => x.MaxAutoSizeHint).Returns(s_screenSize);
+            popupImpl.Setup(x => x.DesktopScaling).Returns(1);
             popupImpl.Setup(x => x.RenderScaling).Returns(1);
             popupImpl.Setup(x => x.PopupPositioner).Returns(positioner);
             popupImpl.Setup(x => x.Position).Returns(()=>position);