title: Detecting touch event outside certain UIView
body: <p>In my app, to click a button will pop up a UIView, now I want to click anywhere outside of the UIView to dismiss the UIView.<br>
  I have tried adding a large transparent button under the UIView, invoke the button action to dismiss the UIView, but the button can't be expanded to Fullscreen because of the top navigationbar and bottom tabbar<br>
  Is any other way to achieve?</p>