UWP useful fragments

PdfViewer.xaml.cs

using System;
using System.Collections.Generic;
using Windows.UI.Xaml;

namespace IbercajaPay.UWP.Controls
{
    using System.Collections.ObjectModel;
    using System.Reactive.Linq;
    using System.Threading.Tasks;
    using Windows.Data.Pdf;
    using Windows.Storage;
    using Windows.Storage.Streams;
    using Windows.UI.Xaml.Media.Imaging;

    public sealed partial class PdfViewer
    {
        public PdfViewer()
        {
            this.InitializeComponent();
            Unloaded += OnUnloaded;
        }

        public static readonly DependencyProperty SourceProperty = DependencyProperty.Register(
            "Uri", typeof(Uri), typeof(PdfViewer), new PropertyMetadata(default(Uri), OnSourceChangedAsync));

        private static IDisposable imageAdder;

        private static async void OnSourceChangedAsync(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs dependencyPropertyChangedEventArgs)
        {

            var target = (PdfViewer)dependencyObject;
            var targetSource = target.Source;

            if (targetSource == null)
            {
                return;
            }

            var pdf = await GetPdfDocument(targetSource);
            
            var imageObs = PdfPages(pdf)
                .ToObservable()
                .SelectMany(GetBitmapFromPage);

            imageAdder = imageObs
                .ObserveOnDispatcher()
                .Subscribe(image => target.Bitmaps.Add(image));
        }

        private void OnUnloaded(object sender, RoutedEventArgs routedEventArgs)
        {
            imageAdder?.Dispose();
            Unloaded -= OnUnloaded;
        }

        private static IEnumerable<PdfPage> PdfPages(PdfDocument pdf)
        {
            for (uint i = 0; i < pdf.PageCount; i++)
            {
                yield return pdf.GetPage(i);
            }
        }

        public ObservableCollection<BitmapSource> Bitmaps { get; } = new ObservableCollection<BitmapSource>();

        private static async Task<PdfDocument> GetPdfDocument(Uri uri)
        {
            var stream = await StorageFile.CreateStreamedFileFromUriAsync("temp.pdf", uri, null);
            var doc = await PdfDocument.LoadFromStreamAsync(await stream.OpenReadAsync());
            return doc;
        }

        private static async Task<BitmapImage> GetBitmapFromPage(PdfPage page)
        {
            var bitmapImage = new BitmapImage();

            using (var pageStream = new InMemoryRandomAccessStream())
            {
                await page.RenderToStreamAsync(pageStream);
                await bitmapImage.SetSourceAsync(pageStream);
            }
            return bitmapImage;
        }

        public Uri Source
        {
            get { return (Uri)GetValue(SourceProperty); }
            set { SetValue(SourceProperty, value); }
        }
    }
}