Migrating from UIWebView to WKWebView

Migrating UIWebView to WKWebView, Swift 4:

Equivalent of shouldStartLoadWithRequest:

func webView(_ webView: WKWebView, decidePolicyFor navigationAction: WKNavigationAction, decisionHandler: @escaping (WKNavigationActionPolicy) -> Void) {
    var action: WKNavigationActionPolicy?

    defer {
        decisionHandler(action ?? .allow)
    }

    guard let url = navigationAction.request.url else { return }

    print(url)

    if navigationAction.navigationType == .linkActivated, url.absoluteString.hasPrefix("http://www.example.com/open-in-safari") {
        action = .cancel                  // Stop in WebView
        UIApplication.shared.openURL(url) // Open in Safari
    }
}

Equivalent of webViewDidStartLoad:

func webView(_ webView: WKWebView, didStartProvisionalNavigation navigation: WKNavigation!) {
    print(String(describing: webView.url))
}

Equivalent of didFailLoadWithError:

func webView(_ webView: WKWebView, didFail navigation: WKNavigation!, withError error: Error) {
    let nserror = error as NSError
    if nserror.code != NSURLErrorCancelled {
        webView.loadHTMLString("404 - Page Not Found", baseURL: URL(string: "http://www.example.com/"))
    }
}

Equivalent of webViewDidFinishLoad:

func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
    print(String(describing: webView.url))
}

Here is the Objective-C methods for the migration:

1. shouldStartLoadWithRequest -> decidePolicyForNavigationAction

Remember to call the decisionHandler:

- (void)webView:(WKWebView *)webView decidePolicyForNavigationAction:(WKNavigationAction *)navigationAction decisionHandler:(void (^)(WKNavigationActionPolicy))decisionHandler {
       if (navigationAction.navigationType == WKNavigationTypeLinkActivated) {

       }
       NSString *url = [navigationAction.request.URL query];
                
       decisionHandler(WKNavigationActionPolicyAllow);
}

2. webViewDidStartLoad -> didStartProvisionalNavigation

- (void)webView:(WKWebView *)webView didStartProvisionalNavigation:(WKNavigation *)navigation {
}

3. webViewDidFinishLoad -> didFinishNavigation

- (void)webView:(WKWebView *)webView didFinishNavigation:(WKNavigation *)navigation {
}

4. didFailLoadWithError -> didFailNavigation

- (void)webView:(WKWebView *)webView didFailNavigation:(WKNavigation *)navigation withError:(NSError *)error {
}

UIWebView => WKWebView Equivalent

UIWebViewDelegate => WKNavigationDelegate

delegate => navigationDelegate
didFailLoadWithError => didFailNavigation
webViewDidFinishLoad => didFinishNavigation
webViewDidStartLoad => didStartProvisionalNavigation
shouldStartLoadWithRequest => decidePolicyForNavigationAction

About shouldStartLoadWithRequest you can write:

func webView(_ webView: WKWebView, decidePolicyFor navigationAction: WKNavigationAction, decisionHandler: @escaping (WKNavigationActionPolicy) -> Void) {
    print("webView:\(webView) decidePolicyForNavigationAction:\(navigationAction) decisionHandler:\(decisionHandler)")
    
    switch navigationAction.navigationType {
        case .linkActivated:
        if navigationAction.targetFrame == nil {
            self.webView?.loadRequest(navigationAction.request)
        }
        if let url = navigationAction.request.url, !url.absoluteString.hasPrefix("http://www.myWebSite.com/example") {
            UIApplication.shared.open(url)
            print(url.absoluteString)
            decisionHandler(.cancel)
        return
        }
        default:
            break
    }
    
    if let url = navigationAction.request.url {
        print(url.absoluteString)
    }
    decisionHandler(.allow)
}

And for the didFailLoadWithError:

func webView(_ webView: WKWebView, didFail navigation: WKNavigation!, withError error: Error) {
    print("webView:\(webView) didFailNavigation:\(navigation) withError:\(error)")
    let testHTML = Bundle.main.path(forResource: "back-error-bottom", ofType: "jpg")
    let baseUrl = URL(fileURLWithPath: testHTML!)

    let htmlString = "myErrorInHTML"
    self.webView.loadHTMLString(htmlString, baseURL: baseUrl)
}