Display a loading icon while a network resource is being downloaded
<p>I'm trying to display a loading icon while my iPhone app downloads a network resource, but I can't figure out how to make it show up correctly.</p>

<p>I searched around and found some details on the UIActivityViewer class, but the available example source code didn't work, and the documentation is kind of terse.</p>

<p>Could someone provide a simple example on how to use this class?</p>
