Xamarin.Forms-Samples/FormulaOneApp/FormulaOneApp.WinPhone/App.xaml

<Application
    x:Class="FormulaOneApp.WinPhone.App"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:phone="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone"
    xmlns:shell="clr-namespace:Microsoft.Phone.Shell;assembly=Microsoft.Phone">

    <!--Recursos de la aplicación-->
    <Application.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="Themes/Pivot.xaml" />
            </ResourceDictionary.MergedDictionaries>
            <local:LocalizedStrings xmlns:local="clr-namespace:FormulaOneApp.WinPhone" x:Key="LocalizedStrings"/>
        </ResourceDictionary>
    </Application.Resources>

    <Application.ApplicationLifetimeObjects>
        <!--Objeto requerido que controla los eventos de duración de la aplicación-->
        <shell:PhoneApplicationService
            Launching="Application_Launching" Closing="Application_Closing"
            Activated="Application_Activated" Deactivated="Application_Deactivated"/>
    </Application.ApplicationLifetimeObjects>

</Application>