如何通过"下拉和释放"手势刷新UIWebView？

class CustomUIWebView: UIWebView {
    var startY: CGFloat = 0
    var isRefreshing = false

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        if let touch = touches.first {
            startY = touch.location(in: self).y
        }
    }

    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        if isRefreshing {
            return
        }

        if let touch = touches.first {
            let currentY = touch.location(in: self).y
            let offsetY = currentY - startY

            if offsetY > 0 {
                // 下拉刷新
            }
        }
    }

    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        if isRefreshing {
            return
        }

        if let touch = touches.first {
            let currentY = touch.location(in: self).y
            let offsetY = currentY - startY

            if offsetY > 0 {
                // 释放刷新
                isRefreshing = true
                // 调用刷新方法
                refresh()
            }
        }
    }

    func refresh() {
        // 刷新逻辑
        isRefreshing = false
    }
}

func refresh() {
    // 刷新逻辑
    isRefreshing = false
}

class ViewController: UIViewController {
    var customWebView: CustomUIWebView!

    override func viewDidLoad() {
        super.viewDidLoad()

        customWebView = CustomUIWebView(frame: view.bounds)
        view.addSubview(customWebView)

        // 加载网页内容
        if let url = URL(string: "https://www.example.com") {
            let request = URLRequest(url: url)
            customWebView.loadRequest(request)
        }
    }
}