title: implementing UIActivityIndicatorView while NSData dataWithContentsOfURL is downloading
body: <p>I am downloading an mp3 using NSData dataWithContentsOfURL:url. This takes a while and while the file is downloading the application hangs. I want to handle well and ideal would like to show the download progress but can't find methods for this.</p>
  
  <p>It is in a UIViewController and I have made a first attempt by putting in a UIActivityIndicatorView and start it spinning before I start the download, then stop it spinning after but nothing appears.</p>
  
  <p>So my question really is please could someone tell me what the best way to handle this is? Thanks so much</p>