public MainPage()
        {
            this.InitializeComponent();
            SystemNavigationManager.GetForCurrentView().AppViewBackButtonVisibility = AppViewBackButtonVisibility.Visible;
            SystemNavigationManager.GetForCurrentView().BackRequested += (s, e) =>
            {
                if (Frame.CanGoBack)
                {
                    Frame.GoBack();
                    e.Handled = true;
                }
            };
        }