From 804d70e44868bc9de59cd61bf0403b482fd366ad Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@gmail.com>
Date: Tue, 7 Apr 2020 14:59:54 +0200
Subject: [PATCH 1/2] Add failing test for #2680.

---
 .../Shapes/PathTests.cs                        | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/tests/Avalonia.Controls.UnitTests/Shapes/PathTests.cs b/tests/Avalonia.Controls.UnitTests/Shapes/PathTests.cs
index 05224c2495..5a9ca410e4 100644
--- a/tests/Avalonia.Controls.UnitTests/Shapes/PathTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/Shapes/PathTests.cs
@@ -1,4 +1,6 @@
 using Avalonia.Controls.Shapes;
+using Avalonia.Media;
+using Avalonia.UnitTests;
 using Xunit;
 
 namespace Avalonia.Controls.UnitTests.Shapes
@@ -12,5 +14,21 @@ namespace Avalonia.Controls.UnitTests.Shapes
 
             target.Measure(Size.Infinity);
         }
+
+        [Fact]
+        public void Subscribes_To_Geometry_Changes()
+        {
+            using var app = UnitTestApplication.Start(TestServices.MockPlatformRenderInterface);
+
+            var geometry = new EllipseGeometry { Rect = new Rect(0, 0, 10, 10) };
+            var target = new Path { Data = geometry };
+
+            target.Measure(Size.Infinity);
+            Assert.True(target.IsMeasureValid);
+
+            geometry.Rect = new Rect(0, 0, 20, 20);
+
+            Assert.False(target.IsMeasureValid);
+        }
     }
 }

From 608efb11403be129f73ca0871aa348df1ad99c30 Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@gmail.com>
Date: Tue, 7 Apr 2020 15:06:28 +0200
Subject: [PATCH 2/2] Invalidate path on geometry change.

Fixes #2680.
---
 src/Avalonia.Controls/Shapes/Path.cs | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/src/Avalonia.Controls/Shapes/Path.cs b/src/Avalonia.Controls/Shapes/Path.cs
index 84c3ededa5..3fd84c0c7b 100644
--- a/src/Avalonia.Controls/Shapes/Path.cs
+++ b/src/Avalonia.Controls/Shapes/Path.cs
@@ -1,3 +1,5 @@
+using System;
+using Avalonia.Data;
 using Avalonia.Media;
 
 namespace Avalonia.Controls.Shapes
@@ -10,6 +12,7 @@ namespace Avalonia.Controls.Shapes
         static Path()
         {
             AffectsGeometry<Path>(DataProperty);
+            DataProperty.Changed.AddClassHandler<Path>((o, e) => o.DataChanged(e));
         }
 
         public Geometry Data
@@ -19,5 +22,26 @@ namespace Avalonia.Controls.Shapes
         }
 
         protected override Geometry CreateDefiningGeometry() => Data;
+
+        private void DataChanged(AvaloniaPropertyChangedEventArgs e)
+        {
+            var oldGeometry = (Geometry)e.OldValue;
+            var newGeometry = (Geometry)e.NewValue;
+
+            if (oldGeometry is object)
+            {
+                oldGeometry.Changed -= GeometryChanged;
+            }
+
+            if (newGeometry is object)
+            {
+                newGeometry.Changed += GeometryChanged;
+            }
+        }
+
+        private void GeometryChanged(object sender, EventArgs e)
+        {
+            InvalidateGeometry();
+        }
     }
 }