Loading an image from a Base64 string in Windows Phone and Windows 8

MyPage.xaml.cs

using System;
using System.IO;
using System.Threading.Tasks;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Media.Imaging;
using Windows.UI.Xaml.Navigation;
using Windows.Web.Http;

// The Blank Page item template is documented at http://go.microsoft.com/fwlink/?LinkID=390556

namespace MyApp
{
    public sealed partial class MyPage : Page
    {
    	public MyPage()
    	{
    	    this.InitializeComponent();
        }
	        
	// # # #
	// Other page logic here
	// # # #

        private string base64Url = "https://gist.githubusercontent.com/asyncwords/c9c5e956396327a2e605/raw/8cb72ef38241851607375aa7edda2dda504e4438/";
        private bool gettingImage = false;

        private async void ImageButton_Click(object sender, RoutedEventArgs e)
        {
            //Check the locking bool so we don't download images multiple times
            if (!gettingImage)
            {
                gettingImage = true;

                //Get the button and change it's text to let the user know what's happening
                var button = sender as Button;
                button.Content = "Getting New Image";

                // TODO: Download or get your Base64 string. I'm using the base64 string located here: 
                // https://gist.githubusercontent.com/asyncwords/c9c5e956396327a2e605/raw/8cb72ef38241851607375aa7edda2dda504e4438/
                
                string base64String = await DownloadImageAsBase64();

                //xaml images cannot use a base64 string as their source. We'll need to create a bitmap image instead. 
                var bitmap = new BitmapImage();

                //Bitmap images use a URI or a stream as their source, so let's convert our base64 string to a stream
                using (var stream = new MemoryStream(Convert.FromBase64String(base64String)))
                {
                    //We're using WinRT (Windows Phone or Windows 8 app) in this example. Bitmaps in WinRT use an IRandomAccessStream as their source
                    await bitmap.SetSourceAsync(stream.AsRandomAccessStream());
                }

                //Bitmap is ready, set it as our image's source
                this.MyImage.Source = bitmap;

                //Set the locking bool to false so the user can download another image
                gettingImage = false;

                //Reset button text
                button.Content = "Get New Image";
            }
        }

        private async Task<string> DownloadImageAsBase64()
        {
            //Create an httpclient and download the string
            var client = new HttpClient();
            var base64String = await client.GetStringAsync(new Uri(base64Url));

            return base64String;
        }
    }
}