WkWebView Message handler doesn't return the value of textbox first time, but it does the secon-CodePudding

So, I have an HTML form with textboxes. I load the form inside WKWebView and I use a message handler inside my Swift app to be able to dump the content of the textboxes and use it later on inside Swift Variables.

The problem is, when I press the Register button which triggers the javascript function that grabs the value of the textboses, first result is blank. Not null, just a space.

If I press the button again, I get the actual content of the textboxes. I've tried using the evaluateJavascript function to get the element by ID, same thing, first time I get nothing, second time I get the expected values.

My ViewController's code:

private var webkitview: WKWebView!
    var lsusername = "";
    var lspassword = "";
    
    @IBOutlet weak var baseview: UIView!
    @IBOutlet weak var registerAccountButton: UIButton!
    
    override func viewDidLoad() {
        super.viewDidLoad()
    
        self.webkitview = WKWebView(frame: self.baseview.bounds, configuration: self.getWKWebViewConfiguration())
        baseview.addSubview(self.appvalleyRegistration)
        baseview.translatesAutoresizingMaskIntoConstraints = false;
        
        let url = URL(string: "https://redacted.com/registrationform.php")!
        webkitview.load(URLRequest(url: url))

    }
    
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        setNeedsStatusBarAppearanceUpdate()
    }
    override var preferredStatusBarStyle: UIStatusBarStyle {
        .darkContent
    }
    
    
    private func getWKWebViewConfiguration() -> WKWebViewConfiguration {
            let userController = WKUserContentController()
            userController.add(self, name: "observer")
            let configuration = WKWebViewConfiguration()
            configuration.userContentController = userController
            return configuration
    }
        
    func userContentController(_ userContentController: WKUserContentController, didReceive message: WKScriptMessage) {
        if let data = message.body as? [String : String], let passw = data["passw"], let email = data["email"] {
            lsusername = email;
            lspassword = passw;
        } else {
            print("No data.");
        }
    }
    
    @IBAction func registerUser(_ sender: Any) {
        webkitview.evaluateJavaScript("submitForm()");
        showUser(email: lsusername, name: lspassword);
    }
    
    private func showUser(email: String, name: String) {
            let userDescription = "\(email) \(name)"
            let alertController = UIAlertController(title: "User", message: userDescription, preferredStyle: .alert)
            alertController.addAction(UIAlertAction(title: "OK", style: .default))
            present(alertController, animated: true)
    }

The alert I trigger using showUser() is blank the first time, and if I press the button again it shows the proper username and password grabbed from the page inside Webkit.

My form:

<body>
<script type="text/javascript">
          function submitForm() {
              var message = {
                passw: document.getElementById("passw").value,
                email: document.getElementById("email").value
              };
              window.webkit.messageHandlers.observer.postMessage(message);
          }
</script>
  <div >
    <h1>Welcome to my site</h1>
    <p>Let's set up your account</p>
    <hr>

    <label for="email"><b>Email</b></label>
    <input type="text" placeholder="Enter Email" name="email" id="email" required>

    <label for="psw"><b>Password</b></label>
    <input type="password" placeholder="Enter Password" name="passw" id="passw" required>

    <label for="psw-repeat"><b>Repeat Password</b></label>
    <input type="password" placeholder="Repeat Password" name="psw-repeat" id="psw-repeat" required>
  </div>
</body>

I don't understand why it works the second time but not the first.

I tried adding sleep() to maybe wait JS to fully complete evaluating but still nothing.

CodePudding user response：

evaluateJavascript is an asynchronous function. Try adding a completion block and calling showUser within it (but make sure you trigger UI updates on the main thread). I think that should fix your immediate problem:

webkitview.evaluateJavaScript("submitForm()") { [weak self] (_, _) in
    DispatchQueue.main.async { [weak self] in
        guard let self = self else { return }
        self.showUser(email: self.lsusername, name: self.lspassword)
    }
}

On a higher level note, would it make more sense to call showUser from within the didReceive function for the WKUserContentController? I haven't used this much, so I could be wrong here.