public AppShell()
        {
            this.Loaded += (sender,args) => {
                Current = this;
            };

            this.InitializeComponent();
            DataContext = new MainPageViewModel();

            this.RootSplitView.RegisterPropertyChangedCallback(
            SplitView.DisplayModeProperty,
            (s, a) =>
            {
                            // Ensure that we update the reported size of the TogglePaneButton when the SplitView's
                            // DisplayMode changes.
                            this.CheckTogglePaneButtonSizeChanged();
            });

            SystemNavigationManager.GetForCurrentView().BackRequested += SystemNavigationManager_BackRequested;
        }