将网页添加到UIViewController时出现问题(Swift)

import UIKit
import WebKit

class WebViewController: UIViewController, WKNavigationDelegate {
    
    var webView: WKWebView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 初始化WKWebView
        webView = WKWebView(frame: self.view.frame)
        webView.navigationDelegate = self
        self.view.addSubview(webView)
        
        // 设置布局约束
        webView.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            webView.topAnchor.constraint(equalTo: self.view.topAnchor),
            webView.bottomAnchor.constraint(equalTo: self.view.bottomAnchor),
            webView.leadingAnchor.constraint(equalTo: self.view.leadingAnchor),
            webView.trailingAnchor.constraint(equalTo: self.view.trailingAnchor)
        ])
        
        // 加载网页
        if let url = URL(string: "https://www.example.com") {
            let request = URLRequest(url: url)
            webView.load(request)
        } else {
            print("Invalid URL")
        }
    }
    
    // WKNavigationDelegate方法
    func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
        print("Page loaded")
    }
    
    func webView(_ webView: WKWebView, didFail navigation: WKNavigation!, withError error: Error) {
        print("Failed to load page: \(error.localizedDescription)")
    }
}