Enable navigationbar or create a panel on top of tabpage xamarin.form

I have this page (TabbedPage) that creates two tabs:

<?xml version="1.0" encoding="utf-8" ?>
<TabbedPage xmlns="http://xamarin.com/schemas/2014/forms"
            xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
            xmlns:views="clr-namespace:Operacional.Views"
            x:Class="Operacional.Views.MainPage">

    <TabbedPage.Children> 
        <NavigationPage Title="Indicadores">
            <NavigationPage.Icon>
                <OnPlatform x:TypeArguments="FileImageSource">
                    <On Platform="iOS" Value="tab_about.png"/>
                </OnPlatform>
            </NavigationPage.Icon>
            <x:Arguments>
                <views:Indicadores />
            </x:Arguments>
        </NavigationPage>
        <NavigationPage Title="Paineis">
            <NavigationPage.Icon>
                <OnPlatform x:TypeArguments="FileImageSource">
                    <On Platform="iOS" Value="tab_feed.png"/>
                </OnPlatform>
            </NavigationPage.Icon>
            <x:Arguments>
                <views:PaineisPage />
            </x:Arguments>
        </NavigationPage>
    </TabbedPage.Children>
</TabbedPage>

What happens is that I'm not able to enable NavigationBar or at least create a panel above the tabpages . The ideal would be to enable NavigationBar , this would be ideal for me. How it works. When you open App , it drops to a login screen. When you log in, you enter MainPage and TabPages on it. If I try to exclude NavigationBar it does not give any errors, but it does not display. Either she is hide or the TabPages are "killing" her. Below my codes. MainPage

[XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class MainPage : TabbedPage
    {
        public MainPage ()
        {
            InitializeComponent ();
            NavigationPage.SetHasNavigationBar(this, true);            
        }
    }

the login screen

public  void Login_Clicked(object sender, EventArgs e)
        {
            LoginService svc = new LoginService();
            LoginRS res = svc.Login(txtUsuario.Text, txtSenha.Text);
            if (res != null && res.Success  )
            {
                App.LooggedUser = res;
                Application.Current.MainPage = new MainPage();
            }
            else if(res != null && ! res.Success)
            {
                lblErroLogin.Text = res.Exception;
            }
            else
            {
                lblErroLogin.Text = "Não foi possível realizar o Login, por favor verifique sua conexão com a Internet";
            }
        }

and my App.xaml.cs

public App()
        {
            InitializeComponent();

            if (!IsUserLoggedIn)
            {
                MainPage = new NavigationPage(new LoginPage());
            }
            else
            {
                MainPage = new NavigationPage(new MainPage());
            }
        }