How to update progressbar from customwebview renderer in xamarin forms for android?

I'm currently developing an app in Xamarin Forms with an Android background so I wanted to create an Android app first and an iOS app later.

I'm new to Xamarin Forms and I'm struggling on how to update a ProgressBar from a WebView using a custom renderer for the webview.

In android you can do something like this, with the progressbar and webview that are in the main_layout.xml

public class MainActivity extends Activity {

    private ProgressBar progressBar;
    private WebView webView;    

    @Override
    protected void onCreate(Bundle savedInstanceState) {     
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main_layout);

        progressBar = (ProgressBar) findViewById(R.id.progress);
        webView = (AdvancedWebView) findViewById(R.id.webView);
        // webview initialisation
        webView.setWebViewClient(new WebViewClient(this) {
            @Override
            public void onPageFinished(WebView view, String url) {
                // update progressbar
                progressBar.setVisibility(View.GONE);
            }
        });
    }
}

In Xamarin Forms I have this layout in MainPage.xaml in the shared project

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

<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="*" />
        <RowDefinition Height="*" />
        <RowDefinition Height="*" />
        <RowDefinition Height="*" />
    </Grid.RowDefinitions>

    <ProgressBar
        x:Name="progress"
        Grid.Row="3"
        HorizontalOptions="FillAndExpand"
        Progress="0"
        VerticalOptions="Center" />

    <WebView
        x:Name="webview"
        Grid.Row="0"
        Grid.RowSpan="4"
        Grid.Column="0"
        HorizontalOptions="FillAndExpand"
        IsVisible="False"
        Source="https://google.com"
        VerticalOptions="FillAndExpand" />

</Grid>

public partial class App : Application
{
    public App ()
    {
        InitializeComponent();

        MainPage = new MainPage(); 
    }
}

And this custom webview render for android in the android project

[assembly: ExportRenderer(typeof(WebView), typeof(CustomWebviewRenderer))]
namespace MyApp.Droid
{
    public class CustomWebviewRenderer : WebViewRenderer
    {
        private readonly Context context;

        public CustomWebviewRenderer(Context context) : base(context)
        {
            this.context = context;
        }

        protected override void OnElementChanged(ElementChangedEventArgs<WebView> e)
        {
            base.OnElementChanged(e);
            var formsWebView = e.NewElement as Xamarin.Forms.WebView;

            if (formsWebView != null)
            {
                var webView = Control as Android.Webkit.WebView;
                webView.SetWebViewClient(new CustomWebViewClient());           
                webView.Settings.LoadWithOverviewMode = true;
                webView.Settings.UseWideViewPort = true;
                SetNativeControl(webView);
            }
        }

        private class CustomWebViewClient : WebViewClient
        {
            public override void OnPageFinished(Android.Webkit.WebView view, string url)
            {
                // how to update progressbar?
                base.OnPageFinished(view, url);
            }

            public override void OnPageStarted(Android.Webkit.WebView view, string url, Bitmap favicon)
            {
                base.OnPageStarted(view, url, favicon);
            }

            public override bool ShouldOverrideUrlLoading(Android.Webkit.WebView view, IWebResourceRequest request)
            {
                return base.ShouldOverrideUrlLoading(view, request);
            }
        }
    }
}

How can I update the ProgressBar that I have in my MainPage.xaml from the OnPageFinished in the CustomWebviewRenderer class to show the webpage has finished loading? Should I use the MainActivity.cs in the Android project?

Can someone point me in the right direction on how to solve this?

from How to update progressbar from customwebview renderer in xamarin forms for android?