title: Determine if a subview is visible in a UIScrollView
body: <p>I've added a view to my app, that contains a UIScrollView, with a number of UITextViews in it's content view. This works perfectly on OS 3.0 and up, but when I test it on my 2.2.1 iPod touch, there is a UITextView bug that stops any text views automatically updating their content when they are scrolled into view - so you have to send them the setNeedsDisplay message.</p>
  
  <p>However, I only want to do this when they start to become visible during the scroll - how do I determine, in the UIScrollView's scrollViewDidScroll delegate method, whether a UITextView is visible in the UIScrollView's frame?</p>
  
  <p>Ta.
  Jools.</p>