UIWebView delegate method shouldStartLoadWithRequest: equivalent in WKWebView?

I have a module inside my iOS 7+ app which is a UIWebView. The html page loads a javascript that creates custom-shaped buttons (using the Raphaeljs library). With UIWebView, I set delegate to self. The delegate method webView: shouldStartLoadWithRequest: navigationType: is called each time one of my custom button is pressed. The requests should not be handled by the html, but rather by the iOS code. So I used a request convention (read somewhere here on stackoverflow) using "inapp" as the scheme of my requests. I then check for the host and take the appropriate action.

This code works fine on iOS 7. But the web views appear blank on iOS 8 (bug?), so I decided to use WKWebView for iOS 8 devices. The web views now render fine (and amazingly faster!), but my buttons have no effect.

I tried using - (WKNaviation *)loadRequest:(NSURLRequest *)request, but it's not called.

I can't find a direct equivalent of the UIWebView delegate method webView: shouldStartLoadWithRequest: navigationType:. What's the best way of handling those requests with WKWebView?

I've been looking for a good explanation myself, but haven't found one. I've used the following in my app and everything seems to work (Edit: updated based on ccoroom's comment):

UIWebViewDelegate     - webView:shouldStartLoadWithRequest:navigationType:
WKNavigationDelegate  - webView:decidePolicyForNavigationAction:decisionHandler:

Here's the other UIWebViewDelegate methods:

UIWebViewDelegate     - webViewDidStartLoad:
WKNavigationDelegate  - webView:didCommitNavigation:

UIWebViewDelegate     - webViewDidFinishLoad:
WKNavigationDelegate  - webView:didFinishNavigation:

UIWebViewDelegate     - webView:didFailLoadWithError:
WKNavigationDelegate  - webView:didFailNavigation:withError:
                      - webView:didFailProvisionalNavigation:withError:

I'd love for someone to confirm this for me though.

Edit: Actually, I've answered the question you had in the title (although I'm no longer confident that webView:didCommitNavigation: is called at the exact same point in the lifecycle), but re-reading your description it looks like what you actually need to know about is how to reimplement a Javascript/Objective-C bridge using WKWebView. So have a look at my other answer.

To answer the original question, the equivalent of webView:shouldStartLoadWithRequest:navigationType: in UIWebView is webView:decidePolicyForNavigationAction:decisionHandler: in WKWebView. These methods are called before each request is made (including the initial request) and provide the ability to allow/disallow it.

Just use the following method , it's a part of WKNavigationDelegate

- (void)webView:(WKWebView *)webView decidePolicyForNavigationAction:(WKNavigationAction *)navigationAction decisionHandler:(void (^)(WKNavigationActionPolicy))decisionHandler {
    
    NSURLRequest *request = navigationAction.request;
    NSString *url = [[request URL]absoluteString];
   
    decisionHandler(WKNavigationActionPolicyAllow);
}

Re-reading your description it looks like what you actually need to know about is how to reimplement a Javascript/Objective-C bridge using WKWebView.

I've just done this myself, following the tutorial at http://tetontech.wordpress.com/2014/07/17/objective-c-wkwebview-to-javascript-and-back/ and the info at http://nshipster.com/wkwebkit/

WKWebView has a built-in way of communicating between Javascript and Objective-C/Swift: WKScriptMessageHandler.

First, include the WebKit headers and WKScriptMessageHandler protocol in your view controller's header:

#import <UIKit/UIKit.h>
#import <WebKit/WebKit.h>
@interface ViewController : UIViewController <WKScriptMessageHandler>

@end

The when initialising your WKWebView, you need to configure it with a script message handler. Name it whatever you want, but to me it seems like naming it for your app makes sense.

    WKWebViewConfiguration *theConfiguration = 
          [[WKWebViewConfiguration alloc] init];
    [theConfiguration.userContentController 
          addScriptMessageHandler:self name:@"myApp"];

    _theWebView = [[WKWebView alloc] initWithFrame:self.view.frame 
                      configuration:theConfiguration];
    [_theWebView loadRequest:request];
    [self.view addSubview:_theWebView];

Now, implement userContentController:didReceiveScriptMessage:. This fires when your webview receives a message, so it does the work you were previously doing with webView:shouldStartLoadWithRequest:navigationType:.

- (void)userContentController:(WKUserContentController *)userContentController 
                        didReceiveScriptMessage:(WKScriptMessage *)message {
    NSDictionary *sentData = (NSDictionary *)message.body;
    NSString *messageString = sentData[@"message"];
    NSLog(@"Message received: %@", messageString);
}

You're now ready to receive messages from Javascript. The function call you need to add to your Javascript is this:

window.webkit.messageHandlers.myApp.postMessage({"message":"Hello there"});

In Swift you can do something like this:

func webView(webView: WKWebView, decidePolicyForNavigationAction navigationAction: WKNavigationAction, decisionHandler: (WKNavigationActionPolicy) -> Void) {
    
    switch navigationAction.request.URLString {
    case "http://action.is.needed/some-action":
        self.someFunc()
        decisionHandler(.Cancel)
        break
    default:
        decisionHandler(.Allow)
        break
    }
    
}

And this is the link in web page:

<a href="http://action.is.needed/some-action">Hello world!</a>

for swift 4.2: (taking from Yifei He 何一非. )

 func webView(_ webView: WKWebView, decidePolicyFor navigationAction: WKNavigationAction, decisionHandler: (WKNavigationActionPolicy) -> Void) {
        
        let url = navigationAction.request.url
        let urlStr = url?.absoluteString
        switch urlStr {
        case BASE_URL:
            //self.someFunc()
            decisionHandler(.cancel)
            break
        default:
            decisionHandler(.allow)
            break
        }
        
    }

You can add Observer for your WKWebView

 static void* keyValueObservingContext = &keyValueObservingContext;

[webView addObserver:self forKeyPath:@"URL" options:0 context:keyValueObservingContext];


- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
 {

if ([keyPath isEqualToString:@"URL"]){
// do something
  }
}

Don't forget to remove it in viewWillDisappear

-(void)viewWillDisappear:(BOOL)animated{
[super viewWillDisappear:animated];
[webView removeObserver:self forKeyPath:@"URL"];
}