fix(controls): Fix NullReferenceException in Arc

src/Wpf.Ui/Controls/Arc/Arc.cs

@@ -26,8 +26,6 @@ namespace Wpf.Ui.Controls;
 /// </example>
 public class Arc : Shape
 {
-    private Viewbox? _rootLayout;
-
     /// <summary>Identifies the <see cref="StartAngle"/> dependency property.</summary>
     public static readonly DependencyProperty StartAngleProperty = DependencyProperty.Register(
         nameof(StartAngle),
@@ -59,6 +57,12 @@ static Arc()
             typeof(Arc),
             new FrameworkPropertyMetadata(PenLineCap.Round, PropertyChangedCallback)
         );
+
+        // Modify the metadata of the StrokeEndLineCap dependency property.
+        StrokeEndLineCapProperty.OverrideMetadata(
+            typeof(Arc),
+            new FrameworkPropertyMetadata(PenLineCap.Round, PropertyChangedCallback)
+        );
     }
 
     /// <summary>
@@ -93,17 +97,6 @@ public SweepDirection SweepDirection
     /// </summary>
     public bool IsLargeArc { get; internal set; } = false;
 
-    private void EnsureRootLayout()
-    {
-        if (_rootLayout != null)
-        {
-            return;
-        }
-
-        _rootLayout = new Viewbox { SnapsToDevicePixels = true };
-        AddVisualChild(_rootLayout);
-    }
-
     /// <inheritdoc />
     protected override Geometry DefiningGeometry => DefinedGeometry();
 
@@ -196,45 +189,12 @@ protected static void PropertyChangedCallback(DependencyObject d, DependencyProp
         control.InvalidateVisual();
     }
 
-    protected override Visual? GetVisualChild(int index)
-    {
-        if (index != 0)
-        {
-            throw new ArgumentOutOfRangeException(nameof(index), "Arc should have only 1 child");
-        }
-
-        EnsureRootLayout();
-
-        return _rootLayout;
-    }
-
-    protected override Size MeasureOverride(Size availableSize)
-    {
-        EnsureRootLayout();
-
-        _rootLayout!.Measure(availableSize);
-        return _rootLayout.DesiredSize;
-    }
-
     protected override Size ArrangeOverride(Size finalSize)
     {
-        EnsureRootLayout();
-
-        _rootLayout!.Arrange(new Rect(default, finalSize));
-        return finalSize;
-    }
-
-    /// <summary>Overrides the default OnRender method to draw the <see cref="Arc" /> element.</summary>
-    /// <param name="drawingContext">A <see cref="DrawingContext" /> object that is drawn during the rendering pass of this <see cref="System.Windows.Shapes.Shape" />.</param>
-    protected override void OnRender(DrawingContext drawingContext)
-    {
-        base.OnRender(drawingContext);
-        Pen pen = new(Stroke, StrokeThickness)
-        {
-            StartLineCap = StrokeStartLineCap,
-            EndLineCap = StrokeStartLineCap,
-        };
+        // Geometry calculations depend on RenderSize, so we need to invalidate visual when size changes.
+        // The base Shape class doesn't do this automatically for custom-sized geometries.
+        InvalidateVisual();
 
-        drawingContext.DrawGeometry(Stroke, pen, DefinedGeometry());
+        return base.ArrangeOverride(finalSize);
     }
 }