判断ScrollView上下滑动

 func scrollViewDidScroll(_ scrollView: UIScrollView) {
        let vel = scrollView.panGestureRecognizer.velocity(in: scrollView)
        if vel.y > 0 {
            //向上滑动
            setToolBarHidden(false)
        }
        else if vel.y < 0 {
            //向下滑动
            setToolBarHidden(true)
        }
    }