UIGravityBehavior &&UICollisionBehavior

import UIKit

class ViewController: UIViewController {

@IBOutlet weak var imageView: UIImageView!

var dynamicAnimator = UIDynamicAnimator()

override func viewDidAppear(animated: Bool) {

super.viewDidAppear(animated)

dynamicAnimator =

UIDynamicAnimator(referenceView: self.view)

//创建并添加重力行为

let gravityBehavior = UIGravityBehavior(items: [self.imageView])

dynamicAnimator.addBehavior(gravityBehavior)

//创建并添加碰撞行为let collisionBehavior =

UICollisionBehavior(items: [self.imageView])

collisionBehavior.translatesReferenceBoundsIntoBoundary = true

dynamicAnimator.addBehavior(collisionBehavior)

}

}