Swift webview: How to call correctly swift code from javascript?

Question

I'm trying to make my javascript interact with swift code but unfortunately i didn't succeed.

For the moment, i just tried to change the headers colors and display a message like you will see in the code below.

Here's my (index.html) code:

<!DOCTYPE html>
<html>
    <head>
        <title>Test</title>
        <meta charset="UTF-8">
    </head>
    <body>
        <h1>WebView Test</h1>
        <script type="text/javascript" src="main.js"></script>
    </body>
</html>

Here's my (main.js -JavaScript) code:

function callNativeApp () {
    try {
        webkit.messageHandlers.callbackHandler.postMessage("Send from JavaScript");
    } catch(err) {
        console.log('error');
    }
}

setTimeout(function () {
    callNativeApp();
}, 5000);

function redHeader() {
    document.querySelector('h1').style.color = "red";
}

Here's my (ViewController.swift) code:

import UIKit
import WebKit

class ViewController: UIViewController, WKScriptMessageHandler {

    @IBOutlet var containerView : UIView! = nil

    var webView: WKWebView?

    override func loadView() {
        super.loadView()

        var contentController = WKUserContentController();
        var userScript = WKUserScript(
            source: "redHeader()",
            injectionTime: WKUserScriptInjectionTime.AtDocumentEnd,
            forMainFrameOnly: true
        )
        contentController.addUserScript(userScript)
        contentController.addScriptMessageHandler(
            self,
            name: "callbackHandler"
        )

        var config = WKWebViewConfiguration()
        config.userContentController = contentController

        self.webView = WKWebView()
        self.view = self.webView!
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        var url = NSURL(fileURLWithPath: NSBundle.mainBundle().pathForResource("index", ofType: "html")!)
        var req = NSURLRequest(URL: url)
        self.webView!.loadRequest(req)
    }

    func userContentController(userContentController: WKUserContentController!,didReceiveScriptMessage message: WKScriptMessage!) {
            if(message.name == "callbackHandler") {
            println("JavaScript is sending a message \(message.body)")
            } }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }


}

Apple's Documentation for loadView developer.apple.com/documentation/uikit/uiviewcontroller/… says: "Your custom implementation of this method should not call super." That may not be obvious in the accepted answer. — robert
– robert, Commented Jan 2, 2019 at 8:26

Nate Cook · Accepted Answer · 2014-09-14 05:15:56Z

17

You have everything set up properly, but you aren't giving your WKWebViewConfiguration instance to the WKWebView. Since the configuration has the details of the Javascript/Swift bridge, you can't talk back and forth.

override func loadView() {
    // ...
    var config = WKWebViewConfiguration()
    config.userContentController = contentController

    self.webView = WKWebView(frame: self.view.frame, configuration: config)
    self.view = self.webView!
}

answered Sep 14, 2014 at 5:15

Nate Cook

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4 Comments

Dev Over a year ago

Please note calling self.view.frame in the loadView() method causes EXC_BAD_ACCESS crash.

Eduard Over a year ago

@Dev what should I call instead self.view.frame if it's casugin EXC_BAD_ACCESS

sandrom Over a year ago

@Dev it only does if you forget to call super.loadView() beforehand

Heitor Over a year ago

What about the MacOS version?

BananaAcid · Accepted Answer · 2015-12-21 16:43:17Z

my 2 cents, using a javascript callback with JSON ... for full class definition and layout, refer to adam's code

import UIKit
import WebKit

class ViewController: UIViewController, WKScriptMessageHandler {
    var webView: WKWebView?
    ...

then

override func loadView() {
    let theConfiguration = WKWebViewConfiguration()
    let contentController = theConfiguration.userContentController

    // alert fix, at start to allow a JS script to overwrite it
    contentController.addUserScript( WKUserScript(
        source: "window.alert = function(message){window.webkit.messageHandlers.messageBox.postMessage({message:message});};",
        injectionTime: WKUserScriptInjectionTime.AtDocumentStart,
        forMainFrameOnly: true
    ) )
    contentController.addScriptMessageHandler(self, name: "messageBox")

    self.webView = WKWebView(frame: self.view.frame, configuration: theConfiguration)

    // and here things like: self.webView!.navigationDelegate = self
    self.view = self.webView!  // fill controllers view
}

and specifically

func userContentController(userContentController: WKUserContentController, didReceiveScriptMessage message: WKScriptMessage) {

    if message.name == "messageBox" {
        let sentData = message.body as! Dictionary<String, String>

        let message:String? = sentData["message"]

        let alertController = UIAlertController(title: nil, message: message, preferredStyle: UIAlertControllerStyle.Alert)
        alertController.addAction(UIAlertAction(title: NSLocalizedString("OK", comment:"btnOK"), style: .Default, handler: nil))
        self.presentViewController(alertController, animated: true) {}
    }
}

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