Customrenderer for TabbedPage

Question

I'm currently trying to use a custom renderer for my TabbedPage. My Page:

<TabbedPage xmlns="http://xamarin.com/schemas/2014/forms"
        xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
        xmlns:d="http://xamarin.com/schemas/2014/forms/design"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        mc:Ignorable="d"
        xmlns:views="clr-namespace:***.Views"
        x:Class="***.Views.MainPage"
        xmlns:utils="clr-namespace:***.Utils"
        BarBackgroundColor="Black" BarTextColor="White"
        xmlns:android="clr-namespace:Xamarin.Forms.PlatformConfiguration.AndroidSpecific;assembly=Xamarin.Forms.Core"
        android:TabbedPage.ToolbarPlacement="Bottom"
        android:TabbedPage.BarTextColor="White"
        android:TabbedPage.BarItemColor="Gray"
        android:TabbedPage.BarSelectedItemColor="White"
        android:TabbedPage.IsSwipePagingEnabled="False"
        CurrentPageChanged="changeTab"
        x:Name="mainTabbedView">

<TabbedPage.Children>
    <NavigationPage Title="1" HeightRequest="20">
        <NavigationPage.Icon>
            <OnPlatform x:TypeArguments="FileImageSource" >
                <On Platform="iOS" Value="pic1"/>
                <On Platform="Android" Value="pic1"/>
            </OnPlatform>
        </NavigationPage.Icon>
        <x:Arguments>
            <views:NewPage />
        </x:Arguments>
    </NavigationPage>

    <NavigationPage Title="2">
        <NavigationPage.Icon>
            <OnPlatform x:TypeArguments="FileImageSource">
                <On Platform="iOS" Value="pic2"/>
                <On Platform="Android" Value="pic2"/>
            </OnPlatform>
        </NavigationPage.Icon>
        <x:Arguments>
            <views:OtherPage />
        </x:Arguments>
    </NavigationPage>

    <NavigationPage Title="3">
        <NavigationPage.Icon>
            <OnPlatform x:TypeArguments="FileImageSource">
                <On Platform="iOS" Value="pic3"/>
                <On Platform="Android" Value="pic3"/>
            </OnPlatform>
        </NavigationPage.Icon>
        <x:Arguments>
            <views:LastPage />
        </x:Arguments>
    </NavigationPage>
</TabbedPage.Children>

And the Renderer:

using Xamarin.Forms;
using Xamarin.Forms.Platform.Android;
using ***.Droid;
using Android.Content;


[assembly: ExportRenderer(typeof(TabbedPage), typeof(CustomTabbedPageRenderer))]

namespace ***.Droid
{
    class CustomTabbedPageRenderer : TabbedRenderer
    {
        public CustomTabbedPageRenderer(Context context) : base(context)
        {
        }
    }
}

I actually want to use the renderer to change the font of the tabs. Unfortunately the tabbar is not visible when I'm using the renderer. Without the renderer the tabbar is shown. Did I forget something?