NavigationPageRenderer.cs

using System.ComponentModel;
using Android.App;
using Clistr.Droid.Renderers;
using Xamarin.Forms;
using Xamarin.Forms.Platform.Android;
#if __APPCOMPAT__
using NavigationRenderer = Xamarin.Forms.Platform.Android.AppCompat.NavigationPageRenderer;
using Toolbar = Android.Support.V7.Widget.Toolbar;
#else
using NavigationRenderer = Xamarin.Forms.Platform.Android.NavigationRenderer;
using Toolbar = Android.App.ActionBar;
#endif

[assembly: ExportRenderer(typeof(NavigationPage), typeof(NavigationPageRenderer))]

namespace Clistr.Droid.Renderers
{
    public class NavigationPageRenderer : NavigationRenderer
    {
        private Toolbar toolbar;

        protected override void OnElementChanged(ElementChangedEventArgs<NavigationPage> e)
        {
            base.OnElementChanged(e);
            SetCustomView(e.NewElement.CurrentPage.GetType().Name);
        }

        private void SetCustomView(string view)
        {
            toolbar.Subtitle = " -> " + view;
        }

        protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
        {
            base.OnElementPropertyChanged(sender, e);
            if (e.PropertyName.Equals("CurrentPage"))
            {
                SetCustomView(((NavigationPage)sender).CurrentPage.GetType().Name);
            }
        }

        public override void OnViewAdded(Android.Views.View child)
        {
            base.OnViewAdded(child);
#if __APPCOMPAT__
            if (child.GetType() == typeof(Toolbar))
            {
                toolbar = (Toolbar)child;
            }
#else
            toolbar = ((Activity)Context).ActionBar;
#endif
        }
    }
}