title: Download file in chunks (Windows Phone)
body: <p>In my application I can download some media files from web. Normally I used <em>WebClient.OpenReadCompleted</em> method to download, decrypt and save the file to IsolatedStorage. It worked well and looked like that:</p>
  
  <pre><code> private void downloadedSong_OpenReadCompleted(object sender, OpenReadCompletedEventArgs e, SomeOtherValues someOtherValues) // delegate, uses additional values
          {
              // Some preparations
  
                  try
                  {
                     if (e.Result != null)
                     {
                      using (isolatedStorageFile = IsolatedStorageFile.GetUserStoreForApplication())
                      {
                          // working with the gained stream, decryption
                          // saving the decrypted file to isolatedStorage
                          isolatedStorageFileStream = new IsolatedStorageFileStream("SomeFileNameHere", FileMode.OpenOrCreate, isolatedStorageFile);
                          // and use it for MediaElement
                          mediaElement.SetSource(isolatedStorageFileStream);
                          mediaElement.Position = new TimeSpan(0);
                          mediaElement.MediaOpened += new RoutedEventHandler(mediaFile_MediaOpened);
  
                          // and some other work
                       }
                      }
                   }
                   catch(Exception ex) 
                   {
                    // try/catch stuff
                   }
             }
  </code></pre>
  
  <p>But after some investigation I found out that with large files(for me it's more than 100 MB) I'm getting <em>OutOfMemory</em> exception during downloading this file. I suppose that's because WebClient.OpenReadCompleted loads the whole stream into RAM and chokes... And I will need more memory to decrypt this stream.</p>
  
  <p>After another investigation, I've found how to divide large file into chunks after OpenReadCompleted event at saving this file to IsolatedStorage(or decryption and then saving in my ocasion), but this would help with only a part of problem... The primary problem is <strong>how to prevent phone chokes during download process</strong>. <strong>Is there a way to download large file in chunks?</strong> Then I could use the found solution to pass through decryption process. (and still I'd need to find a way to load such big file into mediaElement, but that would be another question)</p>
  
  <hr>
  
  <p>Answer:</p>
  
  <pre><code> private WebHeaderCollection headers;
   private int iterator = 0;
   private int delta = 1048576;
   private string savedFile = "testFile.mp3";
  
   // some preparations
   // Start downloading first piece
  
  
  using (IsolatedStorageFile isolatedStorageFile = IsolatedStorageFile.GetUserStoreForApplication())
                      {
                          if (isolatedStorageFile.FileExists(savedFile))
                              isolatedStorageFile.DeleteFile(savedFile);
                      }
  
                      headers = new WebHeaderCollection();
                      headers[HttpRequestHeader.Range] = "bytes=" + iterator.ToString() + '-' + (iterator + delta).ToString();
                      webClientReadCompleted = new WebClient();
                      webClientReadCompleted.Headers = headers;
                      webClientReadCompleted.OpenReadCompleted += downloadedSong_OpenReadCompleted;
                      webClientReadCompleted.OpenReadAsync(new Uri(song.Link));
                      // song.Link was given earlier
  
  private void downloadedSong_OpenReadCompleted(object sender, OpenReadCompletedEventArgs e)
          {
              try
              {
                  if (e.Cancelled == false)
                  {
                      if (e.Result != null)
                      {
                          ((WebClient)sender).OpenReadCompleted -= downloadedSong_OpenReadCompleted;
  
                          using (IsolatedStorageFile myIsolatedStorage = IsolatedStorageFile.GetUserStoreForApplication())
                          {
                              using (IsolatedStorageFileStream fileStream = new IsolatedStorageFileStream(savedFile, FileMode.Append, FileAccess.Write, myIsolatedStorage))
                              {
                                  int mediaFileLength = (int)e.Result.Length;
                                  byte[] byteFile = new byte[mediaFileLength];
                                  e.Result.Read(byteFile, 0, byteFile.Length);
                                  fileStream.Write(byteFile, 0, byteFile.Length); 
  
                                  // If there's something left, download it recursively
                                  if (byteFile.Length &gt; delta)
                                  {
                                      iterator = iterator + delta + 1;
  
                                      headers = new WebHeaderCollection();
                                      headers[HttpRequestHeader.Range] = "bytes=" + iterator.ToString() + '-' + (iterator + delta).ToString();
                                      webClientReadCompleted.Headers = headers;
                                      webClientReadCompleted.OpenReadCompleted += downloadedSong_OpenReadCompleted;
                                      webClientReadCompleted.OpenReadAsync(new Uri(song.Link));
                                  }
                              }
                          }
                      }
                  }
              }
  </code></pre>