Determine if a subview is visible in a UIScrollView

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 sto开发者_高级运维ps any text views automatically updating their content when they are scrolled into view - so you have to send them the setNeedsDisplay message.

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?

Ta. Jools.

---

You have to do the calculation manually whenever the scroll view scrolls. This answer might help.