xamarin 'Forms.Context' is obsolete: 'Context is obsolete as of version 2.5. Please use a local context instead.'

Question

using Android.App;
using Xamarin.Forms;
using xfRutero;

[assembly: Xamarin.Forms.Dependency(typeof(Salir))]

namespace xfRutero
{
    public class Salir : ISalir
    {
        public void closeApplication()
        {

            var activity = (Activity)Forms.Context;
            activity.FinishAffinity();
        }
    }
}

I don't understand where i have to add Android.Content.Context, i have to fix this application, and iam not sure