WKWebView didn't finish loading, when didFinishNavigation is called - Bug in WKWebView?

Question

Goal: To take a screenshot of WKWebView after the website finished loading

Method employed:

• Defined a WKWebView var in UIViewController

• Created an extension method called screen capture() that takes image of WKWebView

• Made my UIViewController to implement WKNavigationDelegate

• Set the wkwebview.navigationDelegate = self ( in the UIViewController init)

• Implemented the didFinishNavigation delegation func in UIViewcontroller to call screen capture extension method for WKWebView

func webView(webView: WKWebView, didFinishNavigation navigation: WKNavigation!) {
    let img = webView.screenCapture()
}

Questions:

• When I debug i simulator, I notice that the control reaches the didFinishNavigation() func even though the website has not yet rendered in the WKWebView
• Correspondingly the image screenshot taken is a white blob.

What am I missing here? I looked at all possible delegate functions for WKWebView and nothing else seem to represent the completion of content loading in WKWebView. Would appreciate help on if there is a work around

---

Update: Adding screenshot code that I am using to take a screenshot for web view

class func captureEntireUIWebViewImage(webView: WKWebView) -> UIImage? {

    var webViewFrame = webView.scrollView.frame
    if (webView.scrollView.contentSize != CGSize(width: 0,height: 0)){
    webView.scrollView.frame = CGRectMake(webViewFrame.origin.x, webViewFrame.origin.y, webView.scrollView.contentSize.width, webView.scrollView.contentSize.height)

    UIGraphicsBeginImageContextWithOptions(webView.scrollView.contentSize, webView.scrollView.opaque, 0)
    webView.scrollView.layer.renderInContext(UIGraphicsGetCurrentContext())
     var image:UIImage = UIGraphicsGetImageFromCurrentImageContext()
     UIGraphicsEndImageContext()

     webView.scrollView.frame = webViewFrame         
     return image
    }

    return nil
 }

Answer 1

WKWebView doesn't use delegation to let you know when content loading is complete (that's why you can't find any delegate method that suits your purpose). The way to know whether a WKWebView is still loading is to use KVO (key-value observing) to watch its loading property. In this way, you receive a notification when loading changes from true to false.

Here's a looping animated gif showing what happens when I test this. I load a web view and respond to its loading property through KVO to take a snapshot. The upper view is the web view; the lower (squashed) view is the snapshot. As you can see, the snapshot does capture the loaded content:

[NSTimer scheduledTimerWithTimeInterval:1.0 repeats:YES block:^(NSTimer * _Nonnull timer) {
    if (self->_webKitView.isLoading == true) {
        NSLog(@"Still loading...");
    }else {
        NSLog(@"Finished loading...");
        [timer invalidate];
        dispatch_async(dispatch_get_main_queue(), ^{
            [self->_activityIndicator stopAnimating];
        });
    }
}];

Answer 2

For those still looking for an answer to this, the marked answer is BS, he just forced his way into getting it accepted.

Using property,

"loading"

and

webView(webView: WKWebView, didFinishNavigation navigation: WKNavigation!)

both do the same thing, indicate if the main resource is loaded.

Now, that does not mean the entire webpage/website is loaded, because it really depends on the implementation of the website. If it needs to load scripts and resources (images, fonts etc) to make itself visible, you'll still see nothing after the navigation is completed, because the network calls made by the website are not tracked by the webview, only the navigation is tracked, so it wouldn't really know when the website loaded completely.

Answer 3

Here is how I solved it:

class Myweb: WKWebView {

    func setupWebView(link: String) {
        let url = NSURL(string: link)
        let request = NSURLRequest(URL: url!)
        loadRequest(request)
        addObserver(self, forKeyPath: "loading", options: .New, context: nil)
    }

    override func observeValueForKeyPath(keyPath: String?, ofObject object: AnyObject?, change: [String : AnyObject]?, context: UnsafeMutablePointer<Void>) {
        guard let _ = object as? WKWebView else { return }
        guard let keyPath = keyPath else { return }
        guard let change = change else { return }
        switch keyPath {
        case "loading":
            if let val = change[NSKeyValueChangeNewKey] as? Bool {
                if val {
                } else {
                    print(self.loading)
                    //do something!
                }
            }
        default:break
        }
    }

    deinit {
        removeObserver(self, forKeyPath: "loading")
    }
}

Update Swift 3.1

override public func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {

    guard let _ = object as? WKWebView else { return }
    guard let keyPath = keyPath else { return }
    guard let change = change else { return }

    switch keyPath {
    case "loading":
        if let val = change[NSKeyValueChangeKey.newKey] as? Bool {
            //do something!
        }
    default:
        break
    }
}

Answer 4

Lots of hand waiving in here, for incomplete solutions. The observer on "loading" is not reliable because when it's switched to NO, the layout hasn't happened yet and you can't get an accurate reading on page size.

The injection of JS into the view to report page size can also be problematic depending on actual page content.

The WKWebView uses, obviously, a scroller (a "WKWebScroller" subclass to be exact). So, your best bet is to monitor that scroller's contentSize.

    - (void) viewDidLoad {
    //...super etc
    [self.webKitView.scrollView addObserver: self
                                 forKeyPath: @"contentSize"
                                    options: NSKeyValueObservingOptionNew
                                    context: nil];
    }

    - (void) dealloc
    {
        // remove observer
        [self.webKitView.scrollView removeObserver: self
                                        forKeyPath: @"contentSize"];
    }

    - (void) observeValueForKeyPath: (NSString*) keyPath
                           ofObject: (id) object
                             change: (NSDictionary<NSKeyValueChangeKey,id>*) change
                            context: (void*) context
    {
        if ([keyPath isEqualToString: @"contentSize"])
        {
            UIScrollView*   scroller    =   (id) object;
            CGSize          scrollFrame =   scroller.contentSize;

            NSLog(@"scrollFrame = {%@,%@}",
                  @(scrollFrame.width), @(scrollFrame.height));
        }
    }

Watch out for the contentSize: it gets triggered A LOT. If your webView is embedded into another scrolling area (like if you're using it as a form element) then when you scroll your entire view, that subview webView will trigger the changes for the same values. So, make sure you dont resize needlessly or cause needless refreshes.

This solution tested on iOS 12 on iPad Air 2 sim off High Sierra XCode 10.

Answer 5

It's not a good choice to check if the page content loaded from swift or objective-c especially for very complex page with many dynamic content.

A better way to inform you ios code from webpage's javascript. This make it very flexible and effective, you can notify ios code when a dom or the page is loaded.

You can check my post here for further info.

Answer 6

You can inject JavaScript into the web view to either wait for onDOMContentLoaded or check the document.readyState state. I have an app that has been doing this for years, and it was the only reliable way to wait for the DOM to be populated. If you need all the images and other resources to be loaded, then you need to wait for the load event using JavaScript. Here are some docs:

https://developer.mozilla.org/en-US/docs/Web/API/Window/DOMContentLoaded_event https://developer.mozilla.org/en-US/docs/Web/API/Window/load_event https://developer.mozilla.org/en-US/docs/Web/API/Document/readyState