Xamarin Dependency Service - Can't get OnActivityResult to be fired.

IDoWork.cs

namespace DependencyServiceDemo.Droid
{
    public interface IDoWork
    {
        void DoSomething();
    }
}

MainActivity.cs

using System;

using Android.App;
using Android.Content.PM;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Android.OS;
using Android.Content;
using DependencyServiceDemo.Droid;

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

namespace DependencyServiceDemo.Droid
{
    [Activity(Label = "DependencyServiceDemo", Icon = "@drawable/icon", Theme = "@style/MainTheme", MainLauncher = true, ConfigurationChanges = ConfigChanges.ScreenSize | ConfigChanges.Orientation)]
    public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsAppCompatActivity, IDoWork
    {
        public void DoSomething()
        {
            System.Diagnostics.Debug.WriteLine("Doing something...");
        }

        protected override void OnCreate(Bundle bundle)
        {
            TabLayoutResource = Resource.Layout.Tabbar;
            ToolbarResource = Resource.Layout.Toolbar;

            base.OnCreate(bundle);

            global::Xamarin.Forms.Forms.Init(this, bundle);
            LoadApplication(new DependencyServiceDemo.App());
        }

        protected override void OnActivityResult(int requestCode, Result resultCode, Intent data)
        {
            base.OnActivityResult(requestCode, resultCode, data);

            System.Diagnostics.Debug.WriteLine("On Activity Result...");
        }
    }
}

MainPage.xaml

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:local="clr-namespace:DependencyServiceDemo"
             x:Class="DependencyServiceDemo.MainPage">

    <Label Text="Welcome to Xamarin Forms!"
           VerticalOptions="Center"
           HorizontalOptions="Center" />

    <Button Text="Click Me" Clicked="onClicked" />
</ContentPage>

MainPage.xaml.cs

using DependencyServiceDemo.Droid;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Xamarin.Forms;

namespace DependencyServiceDemo
{
    public partial class MainPage : ContentPage
    {
        public MainPage()
        {
            InitializeComponent();
        }

        private void onClicked(object sender, EventArgs e)
        {
            //DisplayAlert("No Camera Found", "No Camera Found/Available", "Close");
            DependencyService.Get<IDoWork>().DoSomething();
        }
    }
}