UIView.animateWithDuration(0.2, 
animations: 
{ self.marker.layer.position.y -= 30 },
completion: {(finished) in UIView.animateWithDuration(0.5, delay: 0,
usingSpringWithDamping: 0.2,
initialSpringVelocity: 5.0,
options: UIViewAnimationOptions.CurveEaseOut,
animations: {//弹性参数的调教，可以参见本文的“参考”部分 
self.marker.layer.position.y += 30 }, 
completion: nil)})

var animator : UIDynamicAnimator?override func viewDidLoad() { 
super.viewDidLoad() 
animator = UIDynamicAnimator(referenceView: view)}
override func viewDidAppear(animated: Bool) { 
let gravity = UIGravityBehavior(items: [marker2])//重力 
let elastic = UIDynamicItemBehavior(items: [marker2])//弹性 
elastic.elasticity = 0.6 let collision = UICollisionBehavior(items: [marker2])//边缘 
let endY = marker2.frame.origin.y + marker2.frame.height//
记录marker2的底部坐标 
collision.addBoundaryWithIdentifier("floor", fromPoint: CGPoint(x: 0, y: endY),
toPoint: CGPoint(x: UIScreen.mainScreen().bounds.width, y: endY))//在marker2的底部画一条线，从屏幕左边到屏幕右边 
animator!.addBehavior(collision) 
animator!.addBehavior(gravity) 
animator!.addBehavior(elastic)}

UIView.animateWithDuration(0.2, 
animations: { 
self.marker2.layer.position.y -= 30 }, 
completion: {(finished : Bool) in 
self.animator!.updateItemUsingCurrentState(self.marker2)//如果不update，则animator不知道它的位置被移动过了})