public MainPageViewModel()
        {
            _todoListRepository = new Repositories.TodoListRepository();

            if (Windows.ApplicationModel.DesignMode.DesignModeEnabled)
            {
                // designtime sample data
                var data = _todoListRepository.Sample().Select(x => new ViewModels.TodoListViewModel(x));
                this.TodoLists = new ObservableCollection <ViewModels.TodoListViewModel>(data);
            }
            else
            {
                // update commands
                this.PropertyChanged += (s, e) =>
                {
                    this.AddListCommand.RaiseCanExecuteChanged();
                    this.RemoveListCommand.RaiseCanExecuteChanged();
                };
            }
        }
        public MainPageViewModel()
        {
            _todoListRepository = Repositories.TodoListRepository.GetDefault();

            if (Windows.ApplicationModel.DesignMode.DesignModeEnabled)
            {
                // designtime sample data
                var data = _todoListRepository.Sample().Select(x => new ViewModels.TodoListViewModel(x));
                this.TodoLists = new ObservableCollection<ViewModels.TodoListViewModel>(data);
            }
            else
            {
                // update commands
                this.PropertyChanged += (s, e) =>
                {
                    this.AddListCommand.RaiseCanExecuteChanged();
                    this.RemoveListCommand.RaiseCanExecuteChanged();
                };
            }
        }