title: how to perform action when collision happens in swift? (i'm not using sprite kit)
body: <pre><code> var animator0: UIDynamicAnimator!
  var gravity0: UIGravityBehavior!
  var collision0: UICollisionBehavior!
  </code></pre>
  
  <p>after adding these I made my view fall but when the collision happens I want an action to be performed, I tried as well writing an if statement in the viewdidappear function : if the y coordinate of the view is at an exact point perform action but it didn't work either.</p>