class RotationViewController: UIViewController {

    @IBOutlet weak var wheel: UIImageView!

    override func viewDidLoad() {

        super.viewDidLoad()

        // Do any additional setup after loading the view.

    }

    override func didReceiveMemoryWarning() {

        super.didReceiveMemoryWarning()

        // Dispose of any resources that can be recreated.

    }

    override func viewDidAppear(animated: Bool) {

        super.viewDidAppear(animated)

        UIView.animateWithDuration(1, animations: {

        self.wheel.transform = CGAffineTransformMakeRotation(<#CGFloat#>(M_PI))

        })

    }

}

求解答？？？谢谢了。