UIScrollView暂停NSTimer直到滚动完成

class ViewController: UIViewController, UIScrollViewDelegate {
    var timer: NSTimer?
    var scrollView: UIScrollView!

    override func viewDidLoad() {
        super.viewDidLoad()

        // 创建一个UIScrollView
        scrollView = UIScrollView(frame: view.bounds)
        scrollView.delegate = self
        view.addSubview(scrollView)

        // 创建一个NSTimer
        timer = NSTimer.scheduledTimerWithTimeInterval(1.0, target: self, selector: "timerFired", userInfo: nil, repeats: true)
    }

    // UIScrollViewDelegate方法，当滚动开始时暂停NSTimer
    func scrollViewWillBeginDragging(scrollView: UIScrollView) {
        timer?.pause()
    }

    // UIScrollViewDelegate方法，当滚动结束时恢复NSTimer
    func scrollViewDidEndDragging(scrollView: UIScrollView, willDecelerate decelerate: Bool) {
        if !decelerate {
            timer?.resume()
        }
    }

    // UIScrollViewDelegate方法，当滚动结束时恢复NSTimer
    func scrollViewDidEndDecelerating(scrollView: UIScrollView) {
        timer?.resume()
    }

    // NSTimer的定时器方法
    func timerFired() {
        // 在这里执行定时器的代码
    }
}

extension NSTimer {
    func pause() {
        self.fireDate = NSDate.distantFuture() as Date
    }

    func resume() {
        self.fireDate = NSDate.distantPast() as Date
    }
}