TagEffect.cs

namespace BeatlesApp
{
  public class TagEffect : RoutingEffect
  {
    public TagEffect() : base("BeatlesApp.TagEffect") {}

    public static readonly BindableProperty TagProperty =
      BindableProperty.CreateAttached("Tag", typeof(int), typeof(TagEffect), 0, propertyChanged: OnTagChanged);

    public static int GetTag(BindableObject view)
    {
      return (int)view.GetValue(TagProperty);
    }

    public static void SetTag(BindableObject view, int value)
    {
      view.SetValue(TagProperty, value);
    }

    static void OnTagChanged(BindableObject bindable, object oldValue, object newValue)
    {
      var view = bindable as View;
      if (view == null) { return ; }

      var tag = (int)newValue;
      if (tag > 0)
      {
        view.Effects.Add(new TagEffect());
      }
      else
      {
        var toRemove = view.Effects.FirstOrDefault(e => e is TagEffect);
        if (toRemove != null)
        {
          view.Effects.Remove(toRemove);
        }
      }
    }
  }
}

TagEffect.iOS.cs

[assembly: ResolutionGroupName("BeatlesApp")]
[assembly: ExportEffect(typeof(TagEffect), "TagEffect")]
namespace BeatlesApp.iOS
{
  public class TagEffect : PlatformEffect
  {
    private System.nint _tag;

    protected override void OnAttached()
    {
      _tag = Control.Tag;
      Control.Tag = BeatlesApp.TagEffect.GetTag(Element);
    }

    protected override void OnDetached()
    {
      Control.Tag = _tag;
    }
  }
}