Caching Images downloaded from web on Windows Phone Isolated storage

I was helping on a Windows Phone application where the requirement was to cache the images the phone downloads on the isolated storage for offline viewing.
I wanted a solution which was simple and as transparent as possible. While researching I found  someone wrote a Silverlight converter for loading images from isolated storage. Taking that as a base I created a converted which can

1. Load image from web (http + https), and persist it to isolated storage.
2. In case of network connectivity issues can load the same image from isolated storage. It does that by mapping the http url to a isolated storage location.
3. In case the network is down and the image is neither there in cache, loads a default image, passed as parameter to converter.

Here is the gist for the implementation.

	using System;
	using System.Net;
	using System.Windows;
	using System.Windows.Controls;
	using System.Windows.Documents;
	using System.Windows.Ink;
	using System.Windows.Input;
	using System.Windows.Media;
	using System.Windows.Media.Animation;
	using System.Windows.Shapes;
	using System.Windows.Data;
	using System.IO.IsolatedStorage;
	using System.IO;
	using System.Windows.Media.Imaging;
	namespace Util.Converters
	{
	/// <summary>
	/// Caches the image that gets downloaded as part of Image control Source property.
	/// </summary>
	public class CacheImageFileConverter : IValueConverter
	{
	private static IsolatedStorageFile _storage = IsolatedStorageFile.GetUserStoreForApplication();
	private const string imageStorageFolder = "TempImages";
	public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
	{
	string path = value as string;
	if (String.IsNullOrEmpty(path)) return null;
	Uri imageFileUri = new Uri(path);
	if (imageFileUri.Scheme == "http" || imageFileUri.Scheme == "https")
	{
	if (!Phone.GetIsNetworkAvailable())
	{
	if (_storage.FileExists(GetFileNameInIsolatedStorage(imageFileUri)))
	{
	return ExtractFromLocalStorage(imageFileUri);
	}
	else
	{
	return LoadDefaultIfPassed(imageFileUri, (parameter ?? string.Empty).ToString());
	}
	}
	else
	{
	return DownloadFromWeb(imageFileUri);
	}
	}
	else
	{
	BitmapImage bm = new BitmapImage(imageFileUri);
	return bm;
	}
	}
	private static object LoadDefaultIfPassed(Uri imageFileUri, string defaultImagePath)
	{
	string defaultImageUri = (defaultImagePath ?? string.Empty).ToString();
	if (!string.IsNullOrEmpty(defaultImageUri))
	{
	BitmapImage bm = new BitmapImage(new Uri(defaultImageUri,UriKind.Relative)); //Load default Image
	return bm;
	}
	else
	{
	BitmapImage bm = new BitmapImage(imageFileUri);
	return bm;
	}
	}
	private static object DownloadFromWeb(Uri imageFileUri)
	{
	WebClient m_webClient = new WebClient(); //Load from internet
	BitmapImage bm = new BitmapImage();
	m_webClient.OpenReadCompleted += (o, e) =>
	{
	if (e.Error != null || e.Cancelled) return;
	WriteToIsolatedStorage(IsolatedStorageFile.GetUserStoreForApplication(), e.Result, GetFileNameInIsolatedStorage(imageFileUri));
	bm.SetSource(e.Result);
	e.Result.Close();
	};
	m_webClient.OpenReadAsync(imageFileUri);
	return bm;
	}
	private static object ExtractFromLocalStorage(Uri imageFileUri)
	{
	string isolatedStoragePath = GetFileNameInIsolatedStorage(imageFileUri); //Load from local storage
	using (var sourceFile = _storage.OpenFile(isolatedStoragePath, FileMode.Open, FileAccess.Read))
	{
	BitmapImage bm = new BitmapImage();
	bm.SetSource(sourceFile);
	return bm;
	}
	}
	public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
	{
	throw new NotImplementedException();
	}
	private static void WriteToIsolatedStorage(IsolatedStorageFile storage, System.IO.Stream inputStream, string fileName)
	{
	IsolatedStorageFileStream outputStream = null;
	try
	{
	if (!storage.DirectoryExists(imageStorageFolder))
	{
	storage.CreateDirectory(imageStorageFolder);
	}
	if (storage.FileExists(fileName))
	{
	storage.DeleteFile(fileName);
	}
	outputStream = storage.CreateFile(fileName);
	byte[] buffer = new byte[32768];
	int read;
	while ((read = inputStream.Read(buffer, 0, buffer.Length)) > 0)
	{
	outputStream.Write(buffer, 0, read);
	}
	outputStream.Close();
	}
	catch
	{
	//We cannot do anything here.
	if (outputStream != null) outputStream.Close();
	}
	}
	/// <summary>
	/// Gets the file name in isolated storage for the Uri specified. This name should be used to search in the isolated storage.
	/// </summary>
	/// <param name="uri">The URI.</param>
	/// <returns></returns>
	public static string GetFileNameInIsolatedStorage(Uri uri)
	{
	return imageStorageFolder + "\\" + uri.AbsoluteUri.GetHashCode() + ".img";
	}
	}
	}

view raw CacheImageFileConverter.cs hosted with ❤ by GitHub

To use the converter

1. Import the name space.
2. Declare the converter as resource.
3. Set the Image Source Property to use this converter like this