swift版webview加载网页进度条效果

import UIKitimport WebKitimport SnapKitclass CMWebVC:UIViewController, WKNavigationDelegate {  var webUrl: String? var webView: WKWebView =WKWebView() var progressView:UIProgressView = UIProgressView() var closeBtn: UIButton!  override func initVC() {  webView.addObserver(self, forKeyPath:"estimatedProgress", options: NSKeyValueObservingOptions.new, context:nil)  webView.navigationDelegate =self }  deinit {  webView.removeObserver(self, forKeyPath:"estimatedProgress")  webView.navigationDelegate =nil }  override func viewDidLoad() {  super.viewDidLoad()    // webview  view.addSubview(webView)  webView.snp.makeConstraints { (make)in   make.width.height.equalToSuperview()  }    // progressview  view.addSubview(progressView)  progressView.snp.makeConstraints { (make)in   make.width.equalToSuperview()   make.height.equalTo(3)   make.top.equalToSuperview()  }  progressView.tintColor =UIColor.ColorBgTheme()  progressView.isHidden =true    // load url  if webUrl !=nil {   webView.load(URLRequest(url:URL(string: webUrl!)!))  }    // shear  self.showRightItem(image:"nav_share") {     } }  override func viewWillAppear(_ animated:Bool) {  super.viewWillAppear(animated)  self.closeButton() }  override func viewWillDisappear(_ animated:Bool) {  self.closeBtn.removeFromSuperview() }  func closeButton() {  if self.closeBtn ==nil {   self.closeBtn =UIButton(frame: CGRect(x:44, y: 0, width:44, height: 44))   self.closeBtn.setTitle("关闭", for: .normal)   self.closeBtn.setTitleColor(UIColor.black, for: .normal)   self.closeBtn.addAction({ (button)in    self.navigationController!.popViewController(animated:true)   })   self.navigationController?.navigationBar.addSubview(self.closeBtn)  } }  override func observeValue(forKeyPath keyPath:String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {  // 加载进度  if keyPath == "estimatedProgress" {   let newprogress = change?[.newKey]!as! Float   let oldprogress = change?[.oldKey]as? Float ??0.0      //不要让进度条倒着走...有时候goback会出现这种情况   if newprogress < oldprogress {    return   }      if newprogress == 1 {    progressView.isHidden =true    progressView.setProgress(0, animated:false)   }   else {    progressView.isHidden =false    progressView.setProgress(newprogress, animated:true)   }  } }  func webView(_ webView:WKWebView, didFinish navigation: WKNavigation!) {  progressView.isHidden =true  progressView.setProgress(0, animated:false) }  func webView(_ webView:WKWebView, didFail navigation: WKNavigation!, withError error: Error) {  progressView.isHidden =true  progressView.setProgress(0, animated:false) }  override func navigateBack() {  if webView.canGoBack {   webView.goBack()  }  else {   super.navigateBack()  } }}