How to get JSContext from WKWebView

Question

In UIWebView, I can get JSContext through:

[webView valueForKeyPath:@"documentView.webView.mainFrame.javaScriptContext"]

The same way doesn't work in WKWebView and app crashes when it arrives this line of code.

Is there a way to get JSContext in WKWebView?

thanks in advance.

Unyielding

did you find any solutions for JS callbacks? – Errancy

Answer 1

You cannot obtain the context, because layout and javascript is handled on another process.

Instead, add scripts to your webview configuration, and set your view controller (or another object) as the script message handler.

Now, send messages from JavaScript like so:

window.webkit.messageHandlers.interOp.postMessage(message)

Your script message handler will receive a callback:

- (void)userContentController:(WKUserContentController *)userContentController 
                            didReceiveScriptMessage:(WKScriptMessage *)message{
    NSLog(@"%@", message.body);
}

Farceur

yep, I've already used this method although binding native object to js context is more convenient to handle js callback. I can call js callback through evaluateJavaScript – Unyielding

Make sure to open a bug report. Apple can do some magic in the middle and still give the functionality. Since the project is open source, someone could do it and post a pull request. – Owing

Downside to this is there doesn't seem to be a way to get information about JavaScript errors that occur during execution. – Calvaria

@MasonG.Zhwiti Wrap your JavaScript in try/catch blocks and pass the exceptions to your native code. – Owing

I'm having trouble translating this answer to my specific situation, any suggestions? #58514292 – Pamper

Answer 2

configure your wkwebview like this and add handler accordingly and post message from script in similar pattern

NSString *myScriptSource = @"alert('Hello, World!')";


WKUserScript *s = [[WKUserScript alloc] initWithSource:myScriptSource injectionTime:WKUserScriptInjectionTimeAtDocumentStart forMainFrameOnly:YES];
WKUserContentController *c = [[WKUserContentController alloc] init];
[c addUserScript:s];
// Add a script message handler for receiving  "buttonClicked" event notifications posted from the JS document using window.webkit.messageHandlers.buttonClicked.postMessage script message
[c addScriptMessageHandler:self name:@"buttonClicked"];

WKWebViewConfiguration *conf = [[WKWebViewConfiguration alloc] init];
conf.userContentController = c;

WKWebView *webview = [[WKWebView alloc] initWithFrame:self.view.bounds configuration:conf];
[self.view addSubview:webview];
webview.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
// Do any additional setup after loading the view, typically from a nib.
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://google.com"]];
[webview loadRequest:request];

implement script message handler "WKScriptMessageHandler" with method name

#pragma mark -WKScriptMessageHandler
- (void)userContentController:(WKUserContentController *)userContentController didReceiveScriptMessage:(WKScriptMessage *)message          {
if ([message.name isEqualToString:@"buttonClicked"]) {
self.buttonClicked ++;
}

// JS objects are automatically mapped to ObjC objects
id messageBody = message.body;
if ([messageBody isKindOfClass:[NSDictionary class]]) {
NSString* idOfTappedButton = messageBody[@"ButtonId"];
[self updateColorOfButtonWithId:idOfTappedButton];
}
}

and post the message form js like this

var button = document.getElementById("clickMeButton");
button.addEventListener("click", function() {
    var messgeToPost = {'ButtonId':'clickMeButton'};
    window.webkit.messageHandlers.buttonClicked.postMessage(messgeToPost);
},false);

Aimeeaimil