title: How to detect touch on UICollectionView?
body: <p>I want to disable UICollectionViewController's autorotation whenever there's a finger on the screen, as the iPhone photo app does.</p>
  
  <p>How to do that? </p>
  
  <ul>
  <li>If use tap gesture, how to distinguish different touch states? (The state should be <code>touching</code>, even after finger moving.)</li>
  <li>If use <code>touchBegan:withEvent:</code>, where to put that code? (The hit view can be any subview of UICollectionView.)</li>
  </ul>