ApplicationLifetimeSample.Utlitities.BackButtonManager.BackButtonManager C# (CSharp) Метод

        public BackButtonManager(Frame frame)
        {
            _frame = frame;
            _navigationManager = SystemNavigationManager.GetForCurrentView();
            _navigationManager.AppViewBackButtonVisibility = frame.CanGoBack ? AppViewBackButtonVisibility.Visible : AppViewBackButtonVisibility.Collapsed;
            _navigationManager.BackRequested += OnBackRequested;
        }