工作与文件选择器在windows phone 8.1中选择的图像

我想在windows phone 8.1中使用文件选择器挑选的图像。我选择了一个图像使用以下代码

  private async void gallery_Tapped(object sender, TappedRoutedEventArgs e)
    {
        FileOpenPicker openPicker = new FileOpenPicker();
        openPicker.ViewMode = PickerViewMode.Thumbnail;
        openPicker.SuggestedStartLocation = PickerLocationId.PicturesLibrary;
        openPicker.FileTypeFilter.Add(".jpg");
        openPicker.FileTypeFilter.Add(".jpeg");
        openPicker.FileTypeFilter.Add(".png");
        // Launch file open picker and caller app is suspended and may be terminated if required
        openPicker.PickSingleFileAndContinue();
   }

 public async void ContinueFileOpenPicker(FileOpenPickerContinuationEventArgs args)
        {
            if (args.Files.Count > 0)
            {
                StorageFile file=args.Files[0];
                IRandomAccessStream fileStream = await                     file.OpenAsync(Windows.Storage.FileAccessMode.Read);
                BitmapImage bitmapImage = new BitmapImage();
                bitmapImage.SetSource(fileStream);
                MyImage.Source=bitmapImage;
  }
            else
            {
            }
}

ContinueFileOpenPicker不执行我尝试了这个，但无法理解。这里有谁能一步一步地指导我，我该怎么做才能成功?由于

 protected override void OnActivated(IActivatedEventArgs args)
        {
            var root = Window.Current.Content as Frame;
            var mainPage = root.Content as MainPage;
            if (mainPage != null && args is FileOpenPickerContinuationEventArgs)
            {
                mainPage.ContinueFileOpenPicker(args as FileOpenPickerContinuationEventArgs);
            }
        }