Cleanup Points collection usage, make it use IList

src/Avalonia.Base/Media/PolyLineSegment.cs

@@ -10,8 +10,8 @@ namespace Avalonia.Media
         /// <summary>
         /// Defines the <see cref="Points"/> property.
         /// </summary>
-        public static readonly StyledProperty<Points> PointsProperty
+        public static readonly StyledProperty<IList<Point>> PointsProperty
-            = AvaloniaProperty.Register<PolyLineSegment, Points>(nameof(Points));
+            = AvaloniaProperty.Register<PolyLineSegment, IList<Point>>(nameof(Points));
 
         /// <summary>
         /// Gets or sets the points.
@@ -19,7 +19,7 @@ namespace Avalonia.Media
         /// <value>
         /// The points.
         /// </value>
-        public Points Points
+        public IList<Point> Points
         {
             get => GetValue(PointsProperty);
             set => SetValue(PointsProperty, value);
@@ -37,9 +37,9 @@ namespace Avalonia.Media
         /// Initializes a new instance of the <see cref="PolyLineSegment"/> class.
         /// </summary>
         /// <param name="points">The points.</param>
-        public PolyLineSegment(IEnumerable<Point> points) : this()
+        public PolyLineSegment(IEnumerable<Point> points)
         {
-            Points.AddRange(points);
+            Points = new Points(points);
         }
 
         protected internal override void ApplyTo(StreamGeometryContext ctx)

src/Avalonia.Base/Media/PolylineGeometry.cs

@@ -14,8 +14,8 @@ namespace Avalonia.Media
         /// <summary>
         /// Defines the <see cref="Points"/> property.
         /// </summary>
-        public static readonly DirectProperty<PolylineGeometry, Points> PointsProperty =
+        public static readonly DirectProperty<PolylineGeometry, IList<Point>> PointsProperty =
-            AvaloniaProperty.RegisterDirect<PolylineGeometry, Points>(nameof(Points), g => g.Points, (g, f) => g.Points = f);
+            AvaloniaProperty.RegisterDirect<PolylineGeometry, IList<Point>>(nameof(Points), g => g.Points, (g, f) => g.Points = f);
 
         /// <summary>
         /// Defines the <see cref="IsFilled"/> property.
@@ -23,13 +23,13 @@ namespace Avalonia.Media
         public static readonly StyledProperty<bool> IsFilledProperty =
             AvaloniaProperty.Register<PolylineGeometry, bool>(nameof(IsFilled));
 
-        private Points _points;
+        private IList<Point> _points;
         private IDisposable? _pointsObserver;
 
         static PolylineGeometry()
         {
             AffectsGeometry(IsFilledProperty);
-            PointsProperty.Changed.AddClassHandler<PolylineGeometry>((s, e) => s.OnPointsChanged(e.NewValue as Points));
+            PointsProperty.Changed.AddClassHandler<PolylineGeometry>((s, e) => s.OnPointsChanged(e.NewValue as IList<Point>));
         }
 
         /// <summary>
@@ -43,9 +43,9 @@ namespace Avalonia.Media
         /// <summary>
         /// Initializes a new instance of the <see cref="PolylineGeometry"/> class.
         /// </summary>
-        public PolylineGeometry(IEnumerable<Point> points, bool isFilled) : this()
+        public PolylineGeometry(IEnumerable<Point> points, bool isFilled)
         {
-            Points.AddRange(points);
+            _points = new Points(points);
             IsFilled = isFilled;
         }
 
@@ -56,7 +56,7 @@ namespace Avalonia.Media
         /// The points.
         /// </value>
         [Content]
-        public Points Points
+        public IList<Point> Points
         {
             get => _points;
             set => SetAndRaise(PointsProperty, ref _points, value);
@@ -97,10 +97,10 @@ namespace Avalonia.Media
             return geometry;
         }
 
-        private void OnPointsChanged(Points? newValue)
+        private void OnPointsChanged(IList<Point>? newValue)
         {
             _pointsObserver?.Dispose();
-            _pointsObserver = newValue?.ForEachItem(
+            _pointsObserver = (newValue as IAvaloniaList<Point>)?.ForEachItem(
                 _ => InvalidateGeometry(),
                 _ => InvalidateGeometry(),
                 InvalidateGeometry);

src/Avalonia.Base/Points.cs

@@ -1,6 +1,18 @@
+using System.Collections.Generic;
 using Avalonia.Collections;
 
 namespace Avalonia
 {
-    public sealed class Points : AvaloniaList<Point> { }
+    public sealed class Points : AvaloniaList<Point>
+    {
+        public Points()
+        {
+            
+        }
+
+        public Points(IEnumerable<Point> points) : base(points)
+        {
+            
+        }
+    }
 }

src/Avalonia.Controls/Shapes/Polygon.cs

@@ -1,21 +1,27 @@
+using System.Collections.Generic;
 using Avalonia.Media;
 
 namespace Avalonia.Controls.Shapes
 {
     public class Polygon : Shape
     {
-        public static readonly StyledProperty<Points?> PointsProperty =
+        public static readonly StyledProperty<IList<Point>> PointsProperty =
-            AvaloniaProperty.Register<Polygon, Points?>("Points");
+            AvaloniaProperty.Register<Polygon, IList<Point>>("Points");
 
         static Polygon()
         {
             AffectsGeometry<Polygon>(PointsProperty);
         }
 
-        public Points? Points
+        public Polygon()
         {
-            get { return GetValue(PointsProperty); }
+            Points = new Points();
-            set { SetValue(PointsProperty, value); }
+        }
+        
+        public IList<Point> Points
+        {
+            get => GetValue(PointsProperty);
+            set => SetValue(PointsProperty, value);
         }
 
         protected override Geometry CreateDefiningGeometry()

src/Avalonia.Controls/Shapes/Polyline.cs

@@ -5,8 +5,8 @@ namespace Avalonia.Controls.Shapes
 {
     public class Polyline: Shape
     {
-        public static readonly StyledProperty<Points?> PointsProperty =
+        public static readonly StyledProperty<IList<Point>> PointsProperty =
-            AvaloniaProperty.Register<Polyline, Points?>("Points");
+            AvaloniaProperty.Register<Polyline, IList<Point>>("Points");
 
         static Polyline()
         {
@@ -14,10 +14,15 @@ namespace Avalonia.Controls.Shapes
             AffectsGeometry<Polyline>(PointsProperty);
         }
 
-        public Points? Points
+        public Polyline()
         {
-            get { return GetValue(PointsProperty); }
+            Points = new Points();
-            set { SetValue(PointsProperty, value); }
+        }
+
+        public IList<Point> Points
+        {
+            get => GetValue(PointsProperty);
+            set => SetValue(PointsProperty, value);
         }
 
         protected override Geometry CreateDefiningGeometry()