title: change UIButton default action by gesture recognizer
body: <p>I can't understand the expression in <a href="https://developer.apple.com/library/content/documentation/EventHandling/Conceptual/EventHandlingiPhoneOS/GestureRecognizer_basics/GestureRecognizer_basics.html#//apple_ref/doc/uid/TP40009541-CH2-SW21" rel="nofollow">Event Handling Guide for iOS－Interacting with Other User Interface Controls</a> </p>
  
  <blockquote>
    <p>If you have a custom subclass of one of these controls and you want to change the >default action, attach a gesture recognizer directly to the control instead of to >the parent view. Then, the gesture recognizer receives the touch event first. </p>
  </blockquote>
  
  <p>anyone can give me some example? thx</p>