Pixiview/Pixiview.Android/Renderers/CardViewRenderer.cs

using Android.Content;
using Android.Graphics;
using Android.Views;
using Pixiview.Droid.Renderers;
using Pixiview.UI;
using Xamarin.Forms;
using Xamarin.Forms.Platform.Android;

[assembly: ExportRenderer(typeof(CardView), typeof(CardViewRenderer))]
namespace Pixiview.Droid.Renderers
{
    public class CardViewRenderer : VisualElementRenderer<CardView>
    {
        ViewOutlineProvider original;

        public CardViewRenderer(Context context) : base(context)
        {
        }

        protected override void OnElementChanged(ElementChangedEventArgs<CardView> e)
        {
            base.OnElementChanged(e);

            var element = e.NewElement;
            if (element != null)
            {
                var radius = element.CornerRadius;
                if (radius > 0)
                {
                    original = OutlineProvider;
                    OutlineProvider = new CornerRadiusOutlineProvider(element, radius);
                    ClipToOutline = true;
                }
            }
        }

        protected override void OnDetachedFromWindow()
        {
            OutlineProvider = original;
            base.OnDetachedFromWindow();
        }

        private class CornerRadiusOutlineProvider : ViewOutlineProvider
        {
            private readonly Element element;
            private readonly float radius;

            public CornerRadiusOutlineProvider(Element from, float r)
            {
                element = from;
                radius = r;
            }

            public override void GetOutline(Android.Views.View view, Outline outline)
            {
                var scale = view.Resources.DisplayMetrics.Density;
                var width = (double)element.GetValue(VisualElement.WidthProperty) * scale;
                var height = (double)element.GetValue(VisualElement.HeightProperty) * scale;

                var rect = new Rect(0, 0, (int)width, (int)height);
                outline.SetRoundRect(rect, radius * scale);
            }
        }
    }
}