1details.axml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
   <include
            android:id="@+id/toolbar"
            layout="@layout/toolbar" />
  <FrameLayout
      android:layout_width="fill_parent"
      android:layout_height="0dp"
      android:layout_weight="1"
      android:id="@+id/fragment_frame_layout"/>
</LinearLayout>

2detailsactivity.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using ImageSearch.ViewModel;
using Android.Support.V7.App;

using Toolbar = Android.Support.V7.Widget.Toolbar;
using Xamarin.Forms;
using ImageSearch.Shared.View;
using Xamarin.Forms.Platform.Android.AppCompat;
using Xamarin.Forms.Platform.Android;

namespace ImageSearch.Droid
{
    [Activity(Label = "Details", Icon = "@drawable/icon")]
    public class DetailsActivity : AppCompatActivity
    {

        public static ImageSearchViewModel ViewModel { get; set; }

        protected override void OnCreate(Bundle bundle)
        {
            base.OnCreate(bundle);
            SetContentView(Resource.Layout.details);

            Xamarin.Forms.Forms.Init(this, bundle);

            var toolbar = FindViewById<Toolbar>(Resource.Id.toolbar);
            SetSupportActionBar(toolbar);


            SupportActionBar.Title = ViewModel.SelectedImage.Title;
            // #1 Initialize
            Forms.Init(this, null);
            // #2 Use it
            var frag = new DetailsPage(ViewModel.SelectedImage, ViewModel).CreateFragment(this);

            var ft = FragmentManager.BeginTransaction();
            ft.Replace(Resource.Id.fragment_frame_layout, frag, "main");
            ft.Commit();

        }
    }
}

3navigate.cs

// Now all we need to do is navigate.
adapter.ItemClick += (sender, args) =>
{
    var image = viewModel.Images[args.Position];
    viewModel.SelectedImage = image;
    DetailsActivity.ViewModel = viewModel;

    StartActivity(typeof(DetailsActivity));
};