CatEffectDroid.cs

using System;
using SampleApp.Droid.Effects;
using Xamarin.Forms;
using Xamarin.Forms.Platform.Android;

[assembly: ResolutionGroupName("SuperAwesome")]
[assembly: ExportEffect(typeof(CatEffect), "CatEffect")]
namespace SampleApp.Droid.Effects
{
    public class CatEffect : PlatformEffect
    {
        protected override void OnAttached()
        {
            try
            {
                if (Control is EntryEditText)
                {
                    Control.SetBackgroundResource(Resource.Drawable.cat);
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine("Cannot set property on attached control. Error: ", ex.Message);
            }
        }

        protected override void OnDetached()
        {
            // Back to white.
            Control.SetBackgroundColor(Android.Graphics.Color.White);
        }
    }
}