             fixedSpace
         ]
         toolbarItems = items
-       
+
         if let navigationController = navigationController {
             navigationController.toolbar.barStyle = navigationController.navigationBar.barStyle
             navigationController.toolbar.tintColor = navigationController.navigationBar.tintColor
         }
     }
-    
+
     public override func viewWillAppear(animated: Bool) {
         super.viewWillAppear(animated)
-       
+
         navigationController?.setToolbarHidden(false, animated: animated)
     }
-    
+
     public override func viewWillDisappear(animated: Bool) {
         super.viewWillDisappear(animated)
-        
+
         navigationController?.setToolbarHidden(true, animated: animated)
     }
-    
+
     public override func viewDidDisappear(animated: Bool) {
         super.viewDidDisappear(animated)
-        
+
         UIApplication.sharedApplication().networkActivityIndicatorVisible = false
     }
-    
+
     public override func viewDidLoad() {
         super.viewDidLoad()
-       
+
         updateToolBarItems()
     }
 }
 
 // MARK: WKNavigationDelegate
 extension SimpleWebViewController: WKNavigationDelegate {
-    public func webView(webView: WKWebView, didCommitNavigation navigation: WKNavigation!) {
+    public func webView(webView: WKWebView, didStartProvisionalNavigation navigation: WKNavigation!) {
         UIApplication.sharedApplication().networkActivityIndicatorVisible = true
         updateToolBarItems()
     }
-    
+
     public func webView(webView: WKWebView, didFinishNavigation navigation: WKNavigation!) {
         navigationItem.title = webView.title
         UIApplication.sharedApplication().networkActivityIndicatorVisible = false
         updateToolBarItems()
     }
-    
+
     public func webView(webView: WKWebView, didFailNavigation navigation: WKNavigation!, withError error: NSError) {
         UIApplication.sharedApplication().networkActivityIndicatorVisible = false
         updateToolBarItems()

        webView.allowsBackForwardNavigationGestures = true
        return webView
    }()
    
    lazy private var backBarButtonItem: UIBarButtonItem = {
        let bundle = NSBundle(forClass: self.classForCoder)
        let image = UIImage(named: "SimpleWebViewController.bundle/back", inBundle: bundle, compatibleWithTraitCollection: nil)

    lazy var webView: WKWebView = {
        let webView = WKWebView()
        self.view.addSubview(webView)

        webView.translatesAutoresizingMaskIntoConstraints = false
        self.view.addConstraints([
            NSLayoutConstraint.init(
