如果不在viewWillDisappear中执行此操作，我如何使NSTimer无效/取消？

var faderTimer: NSTimer?
override func viewDidLoad() {
    super.viewDidLoad()

    self.faderTimer = NSTimer.scheduledTimerWithTimeInterval(self.fadeTime, target: self, selector: Selector("fadeBackground"), userInfo: nil, repeats: true)
}
var faderTimer: NSTimer?
override func viewDidL