ElasticViewController.swift

class ViewController: UIViewController {
  @IBAction func handlePan(recognizer: UIPanGestureRecognizer) {
    let currentPoint = recognizer.translationInView(self.view)

    if let stateMachine = self.stateMachine {
        switch recognizer.state {
        case .Began, .Changed:
            stateMachine.keepMoving(currentPoint)
        default:
            stateMachine.stopMoving()
        }
    }
  }
}