public abstract class NavigationItem<T> : NavigationItem
    {
        public NavigationItem(NavigationData data)
            : base(data)
        {
            Items = new ObservableCollection<T>();
        }
        public ObservableCollection<T> Items { get; private set; }
        protected abstract Task<IEnumerable<T>> GetItems(CancellationToken token);
        protected override async Task DoLoad(CancellationToken token)
        {
            var items = await GetItems(token);
            token.ThrowIfCancellationRequested();
            if (items != null)
            {
                await Task.Run(() =>
                {
                    DispatcherLocator.Dispatcher.Invoke(() =>
                    {
                        foreach (var item in items)
                        {
                            Items.Add(item);
                            if (token.IsCancellationRequested)
                                break;
                        }
                    });
                });
            }
        }
        protected override async Task DoUnload()
        {
            await Task.Run(() => DispatcherLocator.Dispatcher.Invoke(() => Items.Clear()));
        }
    }