Xamarin forms Shadow on Frame in Android

It can be very easy in Android platform, but first of all, you need to create your shadow under Drawable folder of Android resources. For example:

<?xml version="1.0" encoding="utf-8" ?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
  <item>
    <shape android:shape="rectangle">
      <solid android:color="#CABBBBBB" />
      <corners android:radius="2dp" />
    </shape>
  </item>

  <item
      android:left="0dp"
      android:right="0dp"
      android:top="0dp"
      android:bottom="2dp">
    <shape android:shape="rectangle">
      <solid android:color="@android:color/white" />
      <corners android:radius="2dp" />
    </shape>
  </item>
</layer-list>

Name this file as "shadow.xml" and place it under the Drawable folder of Android project, then in your RatingInfoFrameRenderer:

public class RatingInfoFrameRenderer : FrameRenderer
{
    protected override void OnElementChanged(ElementChangedEventArgs<Frame> e)
    {
        base.OnElementChanged(e);
        if (e.NewElement != null)
        {
            ViewGroup.SetBackgroundResource(Resource.Drawable.shadow);
        }
    }
}

To change the style of shadow, you can modify the shadow.xml file, for more information about this, you may refer to google's official document: LayerList.

I know this question is old, but there is an updated way of getting a better shadow effect then the accepted answer. inherit from Xamarin.Forms.Platform.Android.FastRenderers.FrameRenderer and then use SetOutlineSpotShadowColor(Color color) to set the shadow color. You can use CardElevation to determine the strength and spread of the shadow as well.

[assembly: ExportRenderer(typeof(Myframe), typeof(MyFrameRenderer))]
namespace MyApp.Droid.Renderers
{
    public class MyFrameRenderer: Xamarin.Forms.Platform.Android.FastRenderers.FrameRenderer
    {
        public MyFrameRenderer(Context context) : base(context)
        {
        }

        protected override void OnElementChanged(ElementChangedEventArgs<Frame> e)
        {
            base.OnElementChanged(e);

            CardElevation = 10;

            if(((App)Application.Current).Theme != Core.Enums.Theme.Dark)
            {
                SetOutlineSpotShadowColor(Xamarin.Forms.Color.Gray.ToAndroid());
            }
            else
            {
                SetOutlineSpotShadowColor(Xamarin.Forms.Color.HotPink.ToAndroid());
            }
        }
    }
}

Hope this helps someone who stumbles in here like I did.