Merge pull request #11233 from AvaloniaUI/fixes/7706-scrollbar-stuck

Fix scrollbar getting stuck in certain situations

src/Avalonia.Base/Layout/LayoutManager.cs

@@ -21,6 +21,7 @@ namespace Avalonia.Layout
         private readonly Layoutable _owner;
         private readonly LayoutQueue<Layoutable> _toMeasure = new LayoutQueue<Layoutable>(v => !v.IsMeasureValid);
         private readonly LayoutQueue<Layoutable> _toArrange = new LayoutQueue<Layoutable>(v => !v.IsArrangeValid);
+        private readonly List<Layoutable> _toArrangeAfterMeasure = new();
         private readonly Action _executeLayoutPass;
         private List<EffectiveViewportChangedListener>? _effectiveViewportChangedListeners;
         private bool _disposed;
@@ -266,9 +267,14 @@ namespace Avalonia.Layout
 
                 if (!control.IsArrangeValid)
                 {
-                    Arrange(control);
+                    if (Arrange(control) == ArrangeResult.AncestorMeasureInvalid)
+                        _toArrangeAfterMeasure.Add(control);
                 }
             }
+
+            foreach (var i in _toArrangeAfterMeasure)
+                InvalidateArrange(i);
+            _toArrangeAfterMeasure.Clear();
         }
 
         private bool Measure(Layoutable control)
@@ -304,19 +310,19 @@ namespace Avalonia.Layout
             return true;
         }
 
-        private bool Arrange(Layoutable control)
+        private ArrangeResult Arrange(Layoutable control)
         {
             if (!control.IsVisible || !control.IsAttachedToVisualTree)
-                return false;
+                return ArrangeResult.NotVisible;
 
             if (control.VisualParent is Layoutable parent)
             {
-                if (!Arrange(parent))
+                if (Arrange(parent) is var parentResult && parentResult != ArrangeResult.Arranged)
-                    return false;
+                    return parentResult;
             }
 
             if (!control.IsMeasureValid)
-                return false;
+                return ArrangeResult.AncestorMeasureInvalid;
 
             if (!control.IsArrangeValid)
             {
@@ -332,7 +338,7 @@ namespace Avalonia.Layout
                 }
             }
 
-            return true;
+            return ArrangeResult.Arranged;
         }
 
         private void QueueLayoutPass()
@@ -435,5 +441,12 @@ namespace Avalonia.Layout
             public Layoutable Listener { get; }
             public Rect Viewport { get; set; }
         }
+
+        private enum ArrangeResult
+        {
+            Arranged,
+            NotVisible,
+            AncestorMeasureInvalid,
+        }
     }
 }

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

@@ -547,5 +547,38 @@ namespace Avalonia.Base.UnitTests.Layout
             Assert.True(root.IsMeasureValid);
             Assert.True(root.IsArrangeValid);
         }
+
+        [Fact]
+        public void GreatGrandparent_Can_Invalidate_Grandparent_Measure_During_Arrange()
+        {
+            // Issue #7706 (second part: scrollbar gets stuck)
+            var child = new LayoutTestControl();
+            var parent = new LayoutTestControl { Child = child };
+            var grandparent = new LayoutTestControl { Child = parent };
+            var greatGrandparent = new LayoutTestControl { Child = grandparent };
+            var root = new LayoutTestRoot { Child = greatGrandparent };
+
+            root.LayoutManager.ExecuteInitialLayoutPass();
+
+            greatGrandparent.DoArrangeOverride = (_, s) =>
+            {
+                grandparent.InvalidateMeasure();
+                return s;
+            };
+
+            child.InvalidateArrange();
+            greatGrandparent.InvalidateArrange();
+
+            root.LayoutManager.ExecuteLayoutPass();
+
+            Assert.True(child.IsMeasureValid);
+            Assert.True(child.IsArrangeValid);
+            Assert.True(parent.IsMeasureValid);
+            Assert.True(parent.IsArrangeValid);
+            Assert.True(greatGrandparent.IsMeasureValid);
+            Assert.True(greatGrandparent.IsArrangeValid);
+            Assert.True(root.IsMeasureValid);
+            Assert.True(root.IsArrangeValid);
+        }
     }
 }