this.Master = new Master();
this.Detail = new NavigationPage(new Detail());

<?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>

[XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class MainPage : TabbedPage
    {
        public MainPage ()
        {
            InitializeComponent ();

            NavigationPage.SetHasNavigationBar(this, true);

            //this.Master = new Master();

           // NavigationPage.BarBackgroundColorProperty. = Color.Gray;
        }
    }