iOS 上滑隐藏导航,下滑显示导航,仿斗鱼导航效果

func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
        let pan = scrollView.panGestureRecognizer
        let velocity = pan.velocity(in: scrollView).y
        
        if velocity < -15 {
            //上滑
            self.navigationController?.setNavigationBarHidden(true, animated: true)
            //状态栏颜色为黑色
            UIApplication.shared.statusBarStyle = .default
            NotificationCenter.default.post(name: NSNotification.Name(rawValue: kUpdateTitleFreamNote), object: nil)
            
        } else if velocity > 15 {
            //下滑
            self.navigationController?.setNavigationBarHidden(false, animated: true)
            //状态栏颜色为白色
            UIApplication.shared.statusBarStyle = .lightContent
            NotificationCenter.default.post(name: NSNotification.Name(rawValue: kInUpdateTitleFreamNote), object: nil)
        }
    }