Windows Store App and PDF Viewer (C#)

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using Windows.Devices.Geolocation;
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;

using Windows.Storage;
using Windows.Storage.AccessCache;
using Windows.Storage.Pickers;
using Windows.Storage.Provider;
using Windows.Storage.Streams;

using Windows.Data.Pdf;
using System.ComponentModel;
using Windows.ApplicationModel;
using System.Collections.ObjectModel;
using Windows.UI.Xaml.Media.Imaging;

// The Blank Page item template is documented at http://go.microsoft.com/fwlink/?LinkId=234238

namespace WindowsStoreApps
{
    /// <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();
        }

        ObservableCollection<FData> items = new ObservableCollection<FData>();

        private void VirtualizingStackPanel_CleanUpVirtualizedItemEvent(object sender, CleanUpVirtualizedItemEventArgs e)
        {
            var item = e.Value as FData;
            item.Dispose();
        }

        private async void btnBrowse_Click(object sender, RoutedEventArgs e)
        {
            FileOpenPicker openPicker = new FileOpenPicker();
            openPicker.ViewMode = PickerViewMode.List;
            openPicker.SuggestedStartLocation = PickerLocationId.DocumentsLibrary;
            openPicker.FileTypeFilter.Add(".pdf");
            StorageFile pdfFile = await openPicker.PickSingleFileAsync();
			if(pdfFile != null)
			{
				var pdfDocument = await PdfDocument.LoadFromFileAsync(pdfFile);
				for (int i = 0; i < pdfDocument.PageCount; i++)
				{
					items.Add(new FData() { PageNumber = i, PdfDoc = pdfDocument, Width = Window.Current.Bounds.Width, Height = Window.Current.Bounds.Height });
				}
				myFlipView.ItemsSource = items;
			}
        }

    }

    public class FData : INotifyPropertyChanged
    {

        public int PageNumber { get; set; }
        public PdfDocument PdfDoc { get; set; }
        public double Height { get; set; }
        public double Width { get; set; }
        private ImageSource _image = null;
        public ImageSource Image
        {
            get
            {
                if (_image == null)
                    Rendering();
                return _image;
            }
            set
            {
                _image = value;
            }
        }

        private async void Rendering()
        {
            using (var page = PdfDoc.GetPage((uint)PageNumber))
            {
                var renderOption = new PdfPageRenderOptions();
                BitmapImage img = new BitmapImage();
                renderOption.DestinationHeight = (uint)(Height);
                InMemoryRandomAccessStream stream = new InMemoryRandomAccessStream();
                await page.RenderToStreamAsync(stream, renderOption);
                img.SetSource(stream);
                _image = img;
                if (PropertyChanged != null)
                    PropertyChanged(this, new PropertyChangedEventArgs("Image"));
                _image = null;
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;

        internal void Dispose()
        {
            _image = null;
        }
    }
}