var url: String?
  var progresslayer = CALayer()
  var webView: WKWebView?
  var button: UIButton?
convenience init(title: String, url: String) {
    self.init()
    self.title = title
    self.url = url
  }

func setupUI() {
    webView = WKWebView(frame: CGRect.init(x: 0, y: 0, width: screenWidth, height: screenHeight-64.0))

    if url == "" {
      url = "http:www.baidu.com"
    }
    let request = URLRequest(url: URL(string: url ?? "http:www.baidu.com")!)
    webView?.load(request)
    webView?.uiDelegate = self
    webView?.navigationDelegate = self;
    view.addSubview(webView!)

    //添加属性监听
    webView?.addObserver(self, forKeyPath: "estimatedProgress", options: .new, context: nil)
    progresslayer.frame = CGRect.init(x: 0, y: 0, width: screenWidth * 0.1, height: 3)
    progresslayer.backgroundColor = UIColor.green.cgColor
    view.layer.addSublayer(progresslayer)
  }

override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
    if keyPath == "estimatedProgress" {
      progresslayer.opacity = 1
      let float = (change?[NSKeyValueChangeKey.newKey] as! NSNumber).floatValue
      progresslayer.frame = CGRect.init(x: 0, y: 0, width: (screenWidth * CGFloat(float)) , height: 3)
      if float == 1 {
        weak var weakself = self
        DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 0.2, execute: {
          weakself?.progresslayer.opacity = 0
        })
        DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 0.8, execute: {
          weakself?.progresslayer.frame = CGRect.init(x: 0, y: 0, width: 0, height: 3);
        })
      }
    }else{
      super.observeValue(forKeyPath: keyPath, of: object, change: change, context: context)
    }
  }

extension KKWebView : WKUIDelegate, WKNavigationDelegate {
  func webView(_ webView: WKWebView, didFailProvisionalNavigation navigation: WKNavigation!, withError error: Error) {
    guard let btn = button else {
      button = UIButton(type: .system)
      button?.frame = CGRect.init(x: 0, y: 3, width: screenWidth, height: screenHeight-64-3)
      button?.backgroundColor = UIColor.white
      button?.setTitleColor(UIColor.darkText, for: .normal)
      button?.setTitle("点击重新加载", for: .normal)
      button?.addTarget(self, action: #selector(loadURL), for: .touchUpInside)
      view.addSubview(button!)
      return
    }
    btn.isHidden = false
  }
}

 func loadURL() {
    button?.isHidden = true
    if url == "" {
      url = "http:www.baidu.com"
    }
    let request = URLRequest(url: URL(string: url ?? "http:www.baidu.com")!)
    webView?.load(request)
  }

deinit {
    webView!.removeObserver(self, forKeyPath: "estimatedProgress")
  }