swift - 扩展类中的字段为空

Question

我创建了一个 WKWebView 来使用我的应用程序，我需要 Swift 与 Javascript 对话，除此之外一切正常!

import UIKit
import WebKit

class FirstViewController: UIViewController {

    var wk: WKWebView!

    override func viewDidLoad() {
        super.viewDidLoad()
        let config = WKWebViewConfiguration()
        let user = WKUserContentController()

        user.add(self, name: "jsHandler")
        config.userContentController = user

        let wk = WKWebView(frame: .zero, configuration: config)
        view.addSubview(wk)
   }   
}

extension FirstViewController: WKScriptMessageHandler {
    func userContentController(_ userContentController: WKUserContentController, didReceive message: WKScriptMessage) {
        if message.name == "jsHandler" {
            // HERE HAPPENS THE ERROR
            self.wk.evaluateJavaScript("chamaLista( '\(value!)' );", completionHandler: { (Any, Error) in })
        }
    }
}

这个错误:

我在 didReceive 函数中添加下一段代码:

extension FirstViewController: WKScriptMessageHandler {
    func userContentController(_ userContentController: WKUserContentController, didReceive message: WKScriptMessage) {
        if message.name == "jsHandler" {
            if self.wk == nil {
                print("WK is Null!")
            }
        }
    }
}

并且:

不能引用扩展类中的对象？？？

Answer 1

您永远不会在 viewDidLoad 中将 webview 分配给 wk:

override func viewDidLoad() {
    ...

    let wk = WKWebView(frame: .zero, configuration: config)
    // assign the local variable to instance property
    self.wk = wk
    view.addSubview(wk)
}

或者只是:

override func viewDidLoad() {
    ...

    // assign directly to instance property, don't use local variable
    wk = WKWebView(frame: .zero, configuration: config)
    view.addSubview(wk)
}