Displaying activity indicator on WKWebView using swift

As commented, you forgot to set the webView delegate:

override func loadView() {    super.loadView()    self.webView = WKWebView()    self.webView.navigationDelegate = self    self.view = self.webView}

You should use the delegate methods for all other purposes, but key path monitoring works fine for this one purpose.

Here is a Swift 4 implementation that works fine.

// Somewhere in your view controllerprivate var loadingObservation: NSKeyValueObservation?private lazy var loadingIndicator: UIActivityIndicatorView = {    let spinner = UIActivityIndicatorView()    spinner.translatesAutoresizingMaskIntoConstraints = false    spinner.color = .black    return spinner}()override func viewDidLoad() {    super.viewDidLoad()    // Setup...    loadingObservation = webView.observe(\.isLoading, options: [.new, .old]) { [weak self] (_, change) in        guard let strongSelf = self else { return }        // this is fine        let new = change.newValue!        let old = change.oldValue!        if new && !old {            strongSelf.view.addSubview(strongSelf.loadingIndicator)            strongSelf.loadingIndicator.startAnimating()            NSLayoutConstraint.activate([strongSelf.loadingIndicator.centerXAnchor.constraint(equalTo: strongSelf.view.centerXAnchor),                                         strongSelf.loadingIndicator.centerYAnchor.constraint(equalTo: strongSelf.view.centerYAnchor)])            strongSelf.view.bringSubview(toFront: strongSelf.loadingIndicator)        }        else if !new && old {            strongSelf.loadingIndicator.stopAnimating()            strongSelf.loadingIndicator.removeFromSuperview()        }    }}

Please, below code which is working fine[Swift 4.2].

@IBOutlet weak var wv: WKWebView!@IBOutlet weak var activityIndicator: UIActivityIndicatorView!override func viewDidLoad() {    super.viewDidLoad()     loadYoutube(videoID: "KqNS7uAvOxk")     }

Now load Youtube Video

 func loadYoutube(videoID:String) {    guard let youtubeURL = URL(string: "https://www.youtube.com/embed/\(videoID)")        else { return }    wv.load( URLRequest(url: youtubeURL) )    wv.navigationDelegate = self}

Implement below this function:

 func showActivityIndicator(show: Bool) {    if show {        activityIndicator.startAnimating()    } else {        activityIndicator.stopAnimating()    }}

Implement below these three delegate method:

   func webView(_ webView: WKWebView, didFinish navigation:     WKNavigation!) {    showActivityIndicator(show: false)}   func webView(_ webView: WKWebView, didStartProvisionalNavigation    navigation: WKNavigation!) {    showActivityIndicator(show: true)}   func webView(_ webView: WKWebView, didFail navigation:    WKNavigation!, withError error: Error) {    showActivityIndicator(show: false)}

Let me know if it is not working.