title: How to detect user input character in UITextView
body: <p>How to detect user input character in UITextView?</p>
  
  <p>For example:(in UITextView NOT UITextField)</p>
  
  <p>when user input letter "a", trigger an event. when user input "do it", trigger another event.
  or input "http://www.stackoverflow.com" trigger an event.</p>
  
  <p>Thanks</p>