Swift : WKWebView : Fatal error: Unexpectedly found nil while unwrapping an Optional value

Question

我正在尝试将子视图添加到 mainView，但有时工作有时出错。我不知道为什么会这样。

怎么了？谢谢

func setURL(url_string : String){
    DispatchQueue.main.async {
        self.webView = WKWebView(frame : CGRect(x: 0.0, y: 0.0, width: UIScreen.main.bounds.width, height: UIScreen.main.bounds.height))

        if let url = URL(string: url_string) {
            self.webView?.navigationDelegate = self
            if let web = self.webView {
                self.mainView.addSubview(web) // got Error Here
            }
            self.webView?.load(URLRequest(url: url))
        }
    }
}

func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
    self.loadingIndicator.stopAnimating()
    self.loadingIndicator.isHidden = true
}

Answer 1

我尝试通过在函数 didFinish 中添加子视图来解决这个问题。谢谢 //mainView 只是 UIView //@IBOutlet weak var mainView: UIView!

func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
    if let web = self.webView { 
        self.mainView.addSubview(web)
    }
    self.loadingIndicator.stopAnimating()
    self.loadingIndicator.isHidden = true
}

Swift : WKWebView : Fatal error: Unexpectedly found nil while unwrapping an Optional value

Swift : WKWebView : Fatal error: Unexpectedly found nil while unwrapping an Optional value

swift

swift3