demo-xf-app-1a/MobileApp1/Views/FlyoutMenuPage.xaml.cs

using MobileApp1.Models;
using System.Threading.Tasks;
using Xamarin.Forms;
using Xamarin.Forms.Xaml;

namespace MobileApp1.Views
{
    [XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class FlyoutMenuPage : ContentPage
    {
        public FlyoutMenuPage()
        {
            InitializeComponent();

            listView1.ItemSelected += listView1_ItemSelected;
        }

        private async void listView1_ItemSelected(object sender, SelectedItemChangedEventArgs e)
        {
            await Task.Run(() =>
            {
                var item = e.SelectedItem as FlyoutPageItem;
                if (item == null)
                {
                    return;
                }

                MainPage mainPage = ContentPageHelper.GetMainPage(this);
                if (mainPage == null)
                {
                    return;
                }

                ContentPageHelper.SetDetailPage(this, item.TargetType);

                Device.BeginInvokeOnMainThread(() =>
                {
                    listView1.SelectedItem = null;

                    mainPage.IsPresented = false;
                });
            });
        }


    }
}