In Windows Phone 7 how can I save a BitmapImage to local storage?

Question

In Windows Phone 7 how can I save a BitmapImage to local storage? I need to save the image for caching and reload if it is requested again in the next few days.

Answer 1

If you save the file into IsolatedStorage you can set a relative path to view it from there.

Here's a quick example saving a file that was included in the XAP (as a resource) into Isolated Storage.

using (IsolatedStorageFile isoStore = IsolatedStorageFile.GetUserStoreForApplication())
{
  if (!isoStore.FileExists(fileName)
  {
    var sr = Application.GetResourceStream(new Uri(fileName, UriKind.Relative));

    using (var br = new BinaryReader(sr.Stream))
    {
      byte[] data = br.ReadBytes((int)sr.Stream.Length);
      string strBaseDir = string.Empty;
      const string DelimStr = "/";
      char[] delimiter = DelimStr.ToCharArray();
      string[] dirsPath = fileName.Split(delimiter);

      // Recreate the directory structure
      for (int i = 0; i < dirsPath.Length - 1; i++)
      {
          strBaseDir = Path.Combine(strBaseDir, dirsPath[i]);
          isoStore.CreateDirectory(strBaseDir);
      }

      using (BinaryWriter bw = new BinaryWriter(isoStore.CreateFile(fileName)))
      {
          bw.Write(data);
      }
    }
  }
}

You may also be interested in the image caching converters created by Ben Gracewood and Peter Nowaks. They both show saving images into isolated storage and loading them from there.

Answer 2

Hi Jamey,

Another approach I've used is to pass the stream you retrieve for the image in your xap straight into an isolated storage file. Not a lot of moving parts.

        using (var isoStore = IsolatedStorageFile.GetUserStoreForApplication()) {

            var bi = new BitmapImage();
            bi.SetSource(picStreamFromXap);
            var wb = new WriteableBitmap(bi);

            using (var isoFileStream = isoStore.CreateFile("pic.jpg")) 
                Extensions.SaveJpeg(wb, isoFileStream, wb.PixelWidth, wb.PixelHeight, 0, 100);

        }