public ItemPage()
        {
            this.InitializeComponent();

            this.navigationHelper = new NavigationHelper(this);
            this.navigationHelper.LoadState += this.NavigationHelper_LoadState;
            this.navigationHelper.SaveState += this.NavigationHelper_SaveState;
        } 
        public PivotPage()
        {
            InitializeComponent();

            ViewModel = new ViewModel();
            this.DataContext = ViewModel;

            InitPivot();

            NavigationCacheMode = NavigationCacheMode.Required;

            _navigationHelper = new NavigationHelper(this);
            _navigationHelper.LoadState += NavigationHelper_LoadState;
            _navigationHelper.SaveState += NavigationHelper_SaveState;
        }