@IBOutlet var tableView: UITableView!
    @IBOutlet var imageViewHeader: UIView!

    //在view出现时添加特性
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        let color = UIColor(white: 1, alpha: 1)
        //添加渐变效果并跟踪着哪个View
        self.navigationController?.navigationBar.ch_addGradient(by: self.tableView,
                                                                barColor: color)

        //添加缩放视差效果并跟踪着哪个View
        self.imageViewHeader.ch_addParallax(by: self.tableView)
    }

    //在view消失时移除特性
    override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)

        //当控制器是消失时，把绑定的跟踪移除
        self.navigationController?.navigationBar.ch_removeGradient()
        self.imageViewHeader.ch_removeParallax()
    }