IOS TabBarItem Badge

Hi,

On one of our items on the tabbedPage menu we want to show a badge value on IOS devices.
I know there is no standard function for this in Xamarin forms and we need to use a Custom Render but how do we implement this?
There is one example on this forum but I think our situation is a little different:
http://forums.xamarin.com/discussion/comment/70217/#Comment_70217

We have one mainPage which derives from TabbedPage.

public partial class MainPage : TabbedPage
    {
        ShoppingCartPage shopCartPage;
        public MainPage()
        {
            InitializeComponent();
            shopCartPage = GetShoppingCartPage();
            this.Children.Add(new NavigationPage(GetActionsPage()) { Title = "Acties" });
            this.Children.Add(new NavigationPage(GetScanPage()) { Title = "Scannen" });
            this.Children.Add(new NavigationPage(GetMainSearchPage()) { Title = "Winkelen" });
            this.Children.Add(new NavigationPage(shopCartPage) { Title = "Winkelmandje" });
            this.Children.Add(new NavigationPage(GetProfilePage()) { Title = "Profiel" });
        }

On the shopCartPage menu item we want to show a badge.
This is the ShopcartPage:

public partial class ShoppingCartPage : ContentPage
    {
        private ShoppingCartListView lvProducts;
        public ShoppingCartPage()
        {
            InitializeComponent();
            LoadProductListViewDetails();
        }

Nothing special going on there.

So I build a custom render for this page:
`[assembly: ExportRenderer(typeof(ShoppingCartPage), typeof(ShoppingCartRender))]

namespace NinaEasyOrderApp.IOS
{

public class ShoppingCartRender : PageRenderer
{
    ShoppingCartPage shoppingCartPage;

    public ShoppingCartRender()
    {

    }

    public override void ViewDidLoad()
    {
        base.ViewDidLoad();
         this.TabBarItem = new UITabBarItem("Initial Title", UIImage.FromBundle("Icon-Small.png"), 4);
        this.TabBarItem.BadgeValue = "3";
        //var navigationCtrller = ViewController as UIViewController;
        //navigationCtrller.TabBarItem = 
        //navigationCtrller.TabBarItem.BadgeValue = "5";
        // BadgeValue did get initialized, but it's not changed 
        // if later on blueNavigationPage.Title gets changed. 
        // **How to update BadgeValue?** 
    }


    protected override void OnElementChanged(VisualElementChangedEventArgs e)
    {
        base.OnElementChanged(e);
        shoppingCartPage = e.NewElement as ShoppingCartPage;

        this.TabBarItem.Title = "Test";

    }
}

}`

But there is no badge and also the title is still "Winkelmandje".....
Anyone knows a solution?