Xamarin BoxRenderer

BoxRenderer_Android.cs

[assembly: ExportRenderer(typeof(Sample.CustomBoxView), typeof(SABoxViewRenderer))]
namespace Sample.Droid.UIRenderers
{
    public class SABoxViewRenderer : BoxRenderer
    {
        public SABoxViewRenderer(Android.Content.Context context) : base(context)
        {

        }
        protected override void OnElementChanged(ElementChangedEventArgs<BoxView> e)
        {
           
            base.OnElementChanged(e);
            if (e.NewElement != null)
            {
                SetWillNotDraw(false);

                e.NewElement.SizeChanged += (sender, er) =>
                {
                    var box = e.NewElement as CustomBoxView;

                    if (box.IsCircular)
                    {
                        bool takeWidth = box.Height <= box.Width;

                        box.HeightRequest = takeWidth ? box.Width : box.Height;
                        box.WidthRequest = takeWidth ? box.Width : box.Height;
                    }

                    Invalidate();
                };

                Invalidate();
            }
        }

        protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
        {
            base.OnElementPropertyChanged(sender, e);
            if (Element == null || e == null) { return; }
            if (e.PropertyName == CustomBoxView.CornerRadiusProperty.PropertyName)
            {
                Invalidate();
            } 
        }
        public override void Draw(Canvas canvas)
        {

            var box = Element as CustomBoxView;
            var cRadiou = (Math.Abs(box.CornerRadius - -9) < 1) ? box.Width / 2 : box.CornerRadius;

            if (box.IsCircular)
            {
                bool takeWidth = box.Height <= box.Width;

                box.HeightRequest = takeWidth ? box.Width : box.Height;
                box.WidthRequest = takeWidth ? box.Width : box.Height;

                cRadiou = box.WidthRequest / 2;
                Invalidate();
            }


            var rect = new Rect();

            var paint = new Paint()
            {
                Color = box.BackgroundColor.ToAndroid(),
                AntiAlias = true,
            };

            GetDrawingRect(rect);
            var radius = (float)(rect.Width() / box.Width * cRadiou);

            //if (box.ClassId?.ToString() == "right") { }
            //var radiusX = radius;
            //var radiusY = radius;

            canvas.DrawRoundRect(new RectF(rect), radius, radius, paint);
            //x,y
        }
    }

BoxRenderer_IOS.cs

[assembly: ExportRenderer(typeof(Sample.CustomBoxView), typeof(SABoxViewRenderer))]
namespace Sample.iOS.UIRenderers
{
    public class SABoxViewRenderer : BoxRenderer
    {
        protected override void OnElementChanged(ElementChangedEventArgs<BoxView> e)
        {
            base.OnElementChanged(e);

            if (Element != null)
            {
                Layer.MasksToBounds = true;
                e.NewElement.SizeChanged += (sender, er) => { UpdateCornerRadius(Element as CustomBoxView); };
                UpdateCornerRadius(Element as CustomBoxView);
            }
        }

        protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
        {
            base.OnElementPropertyChanged(sender, e);

            if (e.PropertyName == CustomBoxView.CornerRadiusProperty.PropertyName)
            {
                UpdateCornerRadius(Element as CustomBoxView);
            }
        }

        void UpdateCornerRadius(CustomBoxView box)
        {
            if (box.IsCircular)
            {
                Layer.CornerRadius = (nfloat)box.Width / 2;
            }
            else
            { 
                Layer.CornerRadius = (nfloat)box.CornerRadius;   
            }
        }
    }
}

BoxRenderer_Pcl.cs

namespace Sample 
{
    public class CustomBoxView : BoxView
    {
        public static readonly BindableProperty CornerRadiusProperty =
         BindableProperty.Create("CornerRadius", typeof(double), typeof(SABoxView), 0.0);

        /// <summary>
        /// Gets or sets the corner radius.
        /// </summary>
        public double CornerRadius
        {
            get { return (double)GetValue(CornerRadiusProperty); }
            set { SetValue(CornerRadiusProperty, value); }
        }
       
        public bool IsCircular { get; set; } 

    }
}