eShopOnContainers/src/eShopOnContainers.Core/Effects/ThemeEffects.cs

using System.Collections.Generic;
using System.Linq;
using Xamarin.Forms;

namespace eShopOnContainers.Core.Effects
{
    public static class ThemeEffects
    {
        public static readonly BindableProperty CircleProperty =
            BindableProperty.CreateAttached("Circle", typeof(bool), typeof(ThemeEffects), false, propertyChanged: OnChanged<CircleEffect, bool>);

        public static bool GetCircle(BindableObject view)
        {
            return (bool)view.GetValue(CircleProperty);
        }

        public static void SetCircle(BindableObject view, bool circle)
        {
            view.SetValue(CircleProperty, circle);
        }


        private static void OnChanged<TEffect, TProp>(BindableObject bindable, object oldValue, object newValue)
            where TEffect : Effect, new()
        {
            var view = bindable as View;
            if (view == null)
            {
                return;
            }

            if (EqualityComparer<TProp>.Equals(newValue, default(TProp)))
            {
                var toRemove = view.Effects.FirstOrDefault(e => e is TEffect);
                if (toRemove != null)
                {
                    view.Effects.Remove(toRemove);
                }
            }
            else
            {
                view.Effects.Add(new TEffect());
            }
        }

        private class CircleEffect : RoutingEffect
        {
            public CircleEffect()
                : base("eShopOnContainers.CircleEffect")
            {
            }
        }
    }
}