1. 监听WKWebView滑动

 public func settingArrow() {
        self.scrollView.rx.observe(CGPoint.self, #keyPath(UIScrollView.contentOffset)).asObservable().subscribe(onNext: { [weak self] (contentOffset) in
            self?.observeWebScroll(contentOffset: contentOffset ?? CGPoint.zero)
        }).disposed(by: self.disposeBag)
    }

2. 通过WKWebViewm,estimatedProgress属性判断是否加载完成

    private func observeWebScroll(contentOffset: CGPoint) {
        if self.estimatedProgress == 1.0 {
            if self.scrollView.contentSize.height > self.bounds.height + 5 {
                if scrollView.contentOffset.y > 0 {
                    topImgV.isHidden = false
                } else {
                    topImgV.isHidden = true
                }
                if scrollView.contentOffset.y + self.bounds.height > self.scrollView.contentSize.height - 1 {
                    bottomImgV.isHidden = true
                } else {
                    bottomImgV.isHidden = false
                }
            } else {
                topImgV.isHidden = true
                bottomImgV.isHidden = true
            }
        }
    }