Could not implement NavigationPageRenderer Custom renderer xamarin form

Question

I have google a lot about building CustomRenderer to display custom navigationpage on xamarin form (to display gradient on navigationbar) but did not succeed. here is my code:

using System;
using System.Collections.Generic;
using System.Text;
using Xamarin.Forms;

namespace BillerApp
{
    public class GradientNavigationBar: NavigationPage
    {
        public GradientNavigationBar(Page page): base(page)
        {

        }
        public GradientNavigationBar() : base()
        {

        }

        public static readonly BindableProperty StartColorProperty = BindableProperty.Create(
            nameof(StartColor),
            typeof(Color),
            typeof(GradientNavigationBar),
            Color.Default);

        public static readonly BindableProperty EndColorProperty = BindableProperty.Create(
            nameof(EndColor),
            typeof(Color),
            typeof(GradientNavigationBar),
            Color.Default);

        public Color StartColor {
            get { return (Color)GetValue(StartColorProperty); }
            set { SetValue(StartColorProperty, value); }
        }

        public Color EndColor
        {
            get { return (Color)GetValue(EndColorProperty); }
            set { SetValue(EndColorProperty, value); }
        }


    }
}

and following is the renderer on Xamarin.Droid

using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Xamarin.Forms;
using BillerApp;
using Xamarin.Forms.Platform.Android;
using Android.Graphics.Drawables;
using BillerApp.Droid;
using System.ComponentModel;

[assembly: ExportRenderer(typeof(GradientNavigationBar), typeof(GrandientNavigationBarRenderer))]
namespace BillerApp.Droid
{    
    [Activity(Name = "com.companyname.BillerApp.MainActivity")]
    public class GrandientNavigationBarRenderer: Xamarin.Forms.Platform.Android.AppCompat.NavigationPageRenderer
    {

        //public GrandientNavigationBarRenderer(Context context): base(context){} //can not use this constructor

        protected override void OnElementChanged(ElementChangedEventArgs<NavigationPage> e)
        {
            base.OnElementChanged(e);       // I got Invalid Cast Exception if Inherit from NavigationRenderer

            if (e.OldElement != null || Element == null)
            {
                return;
            }

            var p = this.Element as GradientNavigationBar;
            var context = (Activity)this.Context;


            var sc = new int[] { p.StartColor.ToAndroid(), p.EndColor.ToAndroid() };
            var grad = new GradientDrawable(GradientDrawable.Orientation.TopBottom, sc);

            var t = context.ActionBar;   // here i got null       
            t.SetSplitBackgroundDrawable(grad);

            context.ActionBar.SetBackgroundDrawable(grad);
        }

    }
}

this is what i am trying to achieve:

I am using VS 2015 Community edition and have updated SDK tools to date

Answer 1

I would do it simply by adding something like this to your layout folder:

toolbar_gradient.xml

<gradient
android:type="linear"
android:startColor="#F3A183"
android:endColor="#EC6F66"
android:angle="270"/>
</shape>

Then in your Toolbar.xml add this line of code:

android:background="@layout/toolbar_gradient"