活动指示器在WKWebView加载完成后不会停止旋转

import UIKit
import WebKit

class ViewController: UIViewController, WKNavigationDelegate {

    var webView: WKWebView!
    var activityIndicator: UIActivityIndicatorView!

    override func viewDidLoad() {
        super.viewDidLoad()

        webView = WKWebView(frame: view.bounds)
        webView.navigationDelegate = self
        view.addSubview(webView)

        activityIndicator = UIActivityIndicatorView(style: .gray)
        activityIndicator.center = view.center
        view.addSubview(activityIndicator)
        
        let url = URL(string: "https://www.example.com")
        let request = URLRequest(url: url!)
        webView.load(request)
    }

    func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
        activityIndicator.stopAnimating()
    }
}