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.

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); } 

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);