MasterDetailPage doesn't show

Hi,
I'm trying to make a masterdetailpage but I can't figure out why it doesn't work.
Can someone tell me what I'm doing wrong?

that's my code

App.xaml.cs

                public App() : this(null) { }

                public App(IPlatformInitializer initializer) : base(initializer) { }

                protected override async void OnInitialized()
                {
                    InitializeComponent();

                    await NavigationService.NavigateAsync("Navigation/MainPage");
                }

                protected override void RegisterTypes(IContainerRegistry containerRegistry)
                {
                    containerRegistry.RegisterForNavigation<NavigationPage>("Navigation");
                    containerRegistry.RegisterForNavigation<MainPage>();
                    containerRegistry.RegisterForNavigation<Page1>();
                    containerRegistry.RegisterForNavigation<Page2>();
                    containerRegistry.RegisterForNavigation<Page3>();
                    containerRegistry.RegisterForNavigation<MasterPage>("Index");
                }

MasterPage.xaml

<MasterDetailPage xmlns="http://xamarin.com/schemas/2014/forms"
                  xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
                  xmlns:prism="clr-namespace:Prism.Mvvm;assembly=Prism.Forms"
                  prism:ViewModelLocator.AutowireViewModel="True"
                  x:Class="masterDetailPagePrism.Views.MasterPage">

    <MasterDetailPage.Master>
        <NavigationPage>
            <x:Arguments>
                <ContentPage Title="Menu">
                    <StackLayout Padding="20">
                        <!-- TODO: // Update the Layout and add some real menu items  -->
                        <Button Text="ViewA" Command="{Binding ViewA}"/>
                        <Button Text="ViewA" Command="{Binding ViewB}"/>
                        <Button Text="ViewA" Command="{Binding ViewC}"/>
                    </StackLayout>
                </ContentPage>
            </x:Arguments>
        </NavigationPage>

    </MasterDetailPage.Master>

</MasterDetailPage>

MainPageViewModel.cs

    public class MainPageViewModel : ViewModelBase
    {
        public DelegateCommand goTo { get; set; }

        INavigationService _navService;

        public MainPageViewModel(INavigationService navigationService)
            : base(navigationService)
        {
            Title = "Main Page";

            _navService = navigationService;

            goTo = new DelegateCommand(goToNext);
        }

        public void goToNext()
        {
            _navService.NavigateAsync("/Index/Navigation/Page1");
        }
    }

I'm using Xamarin.Forms 3.2 with Prism

Thanks