UIKitDynamics - Gravity_Collision

var dynamicAnimator   : UIDynamicAnimator!
var gravityBehavior   : UIGravityBehavior!
var collisionBehavior : UICollisionBehavior!

dynamicAnimator = UIDynamicAnimator(referenceView: self.view) //1

gravityBehavior = UIGravityBehavior(items: [button]) //2
dynamicAnimator.addBehavior(gravityBehavior) //3

collisionBehavior = UICollisionBehavior(items: [button]) //4
collisionBehavior.translatesReferenceBoundsIntoBoundary = true //5
dynamicAnimator.addBehavior(collisionBehavior) //6