iPhone的UITextView - 你怎么知道你追加的文字何时不在视野范围内

I have a UITextView that I am appending texts to from time to time, but I am unable to find an API that tells me whether the text I am appending is out of view or not so I can send a scrollToRange message to UITextView. Is there a way to do this?I have a UITextView that I am appending texts t