UITextView自动向下滚动

textView.scrollRangeToVisible(NSMakeRange(textView.text.count - 1, 1))

extension UITextView {
    func scrollToBottom() {
        let bottom = NSMakeRange(text.count - 1, 1)
        scrollRangeToVisible(bottom)
    }
}

// 在需要滚动到底部时调用
textView.scrollToBottom()

let bottom = NSMakeRange(textView.text.count - 1, 1)
textView.layoutManager.scrollToCharacterAtIndex(bottom.location)

let bottomOffset = CGPointMake(0, textView.contentSize.height - textView.bounds.size.height)
textView.setContentOffset(bottomOffset, animated: true)