自定义 UINavigation的 UIBarButtonItem 动作报错

运行时报错:

2015-08-09 12:01:24.743 MeApp[32055:3225029] -[MeApp.FeedBackViewController commit]: unrecognized selector sent to instance 0x7fe36155d9c0

    override func viewDidLoad() {
        super.viewDidLoad()
        self.descTextView.delegate = self
        self.navigationItem.setHidesBackButton(false, animated: true)

        descTextView.layer.borderWidth = 1.0
        descTextView.layer.borderColor = UIColor.grayColor().CGColor
        descTextView.text = "问题描述(必填)"
        descTextView.textColor = UIColor.lightGrayColor()

        var rightBtn = UIBarButtonItem(barButtonSystemItem: UIBarButtonSystemItem.Cancel,
            target: self, action: "commit")
        self.navigationItem.setRightBarButtonItems([rightBtn], animated: true)
    }

    private func commit() {
        logger.debug("commit..........")
    }

去掉 commit 的 private 又会正常, 不明白为什么

2015-08-09 12:020