ISupportIncrementalLoading on UI thread

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices.WindowsRuntime;
using System.Threading;
using System.Threading.Tasks;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Windows.UI.Core;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Controls.Primitives;
using Windows.UI.Xaml.Data;
using Windows.UI.Xaml.Input;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Navigation;

// The Blank Page item template is documented at http://go.microsoft.com/fwlink/?LinkId=402352&clcid=0x409

namespace TestIncremental
{
    /// <summary>
    /// An empty page that can be used on its own or navigated to within a Frame.
    /// </summary>
    public sealed partial class MainPage : Page
    {
        public MainPage()
        {
            this.InitializeComponent();

            List.ItemsSource = new TestCollection();
        }
    }

    public abstract class SemaphoreCollection<T> : ObservableCollection<T>, ISupportIncrementalLoading
    {
        private CoreDispatcher _dispatcher;
        private SemaphoreSlim _wait;

        public bool HasMoreItems { get; set; }

        public SemaphoreCollection()
        {
            _dispatcher = Window.Current.Dispatcher;
            _wait = new SemaphoreSlim(0);

            HasMoreItems = true;
        }

        public IAsyncOperation<LoadMoreItemsResult> LoadMoreItemsAsync(uint count)
        {
            return Task.Run(() =>
            {
                LoadMoreItemsInternal(count);
                _wait.Wait();

                return new LoadMoreItemsResult { Count = count };
            }).AsAsyncOperation();
        }

        private async void LoadMoreItemsInternal(uint count)
        {
            await _dispatcher.RunAsync(CoreDispatcherPriority.Normal, async () =>
            {
                await LoadMoreItems(count);
                _wait.Release();
            });
        }

        protected abstract Task LoadMoreItems(uint count);
    }

    public class TestCollection : SemaphoreCollection<string>
    {
        protected override async Task LoadMoreItems(uint count)
        {
            await Task.Delay(1000);
            for (int i = 0; i < count; i++)
            {
                Add($"Item {Count}");
            }
        }
    }
}