Merge pull request #8455 from ltetak/effectiveViewportChangedListeners

EffectiveViewportChangedListeners thread safety improved

src/Avalonia.Base/Layout/LayoutManager.cs

@@ -350,7 +350,7 @@ namespace Avalonia.Layout
                 {
                     for (var i = 0; i < count; ++i)
                     {
-                        var l = _effectiveViewportChangedListeners[i];
+                        var l = listeners[i];
 
                         if (!l.Listener.IsAttachedToVisualTree)
                         {
@@ -362,7 +362,7 @@ namespace Avalonia.Layout
                         if (viewport != l.Viewport)
                         {
                             l.Listener.EffectiveViewportChanged(new EffectiveViewportChangedEventArgs(viewport));
-                            _effectiveViewportChangedListeners[i] = new EffectiveViewportChangedListener(l.Listener, viewport);
+                            l.Viewport = viewport;
                         }
                     }
                 }
@@ -414,7 +414,7 @@ namespace Avalonia.Layout
             }
         }
 
-        private readonly struct EffectiveViewportChangedListener
+        private class EffectiveViewportChangedListener
         {
             public EffectiveViewportChangedListener(ILayoutable listener, Rect viewport)
             {
@@ -423,7 +423,7 @@ namespace Avalonia.Layout
             }
 
             public ILayoutable Listener { get; }
-            public Rect Viewport { get; }
+            public Rect Viewport { get; set; }
         }
     }
 }

tests/Avalonia.Base.UnitTests/Layout/LayoutableTests_EffectiveViewportChanged.cs

@@ -312,6 +312,30 @@ namespace Avalonia.Base.UnitTests.Layout
             });
         }
 
+        [Fact]
+        public async Task Event_Unsubscribed_While_Inside_Callback()
+        {
+            await RunOnUIThread.Execute(async () =>
+            {
+                var root = CreateRoot();
+                var target = new Canvas();
+                var raised = 0;
+
+                void OnTargetOnEffectiveViewportChanged(object s, EffectiveViewportChangedEventArgs e)
+                {
+                    target.EffectiveViewportChanged -= OnTargetOnEffectiveViewportChanged;
+                    ++raised;
+                }
+                target.EffectiveViewportChanged += OnTargetOnEffectiveViewportChanged;
+
+                root.Child = target;
+
+                await ExecuteInitialLayoutPass(root);
+
+                Assert.Equal(1, raised);
+            });
+        }
+
         private TestRoot CreateRoot() => new TestRoot { Width = 1200, Height = 900 };
 
         private Task ExecuteInitialLayoutPass(TestRoot root)