title: How do I tell if a UIView is visible and on screen?
body: <p>If I have a <code>UIView</code> (or <code>UIView</code> subclass) that is visible, how can I tell if it's currently being shown on the screen (as opposed to, for example, being in a section of a scroll view that is currently off-screen)?</p>
  
  <p>To maybe give you a better idea of what I mean, <code>UITableView</code> has a couple of methods for determining the set of currently visible cells. I'm looking for some code that can make a similar determination for any given <code>UIView</code>.</p>