如何在导航栏中创建一个带有UIActivityIndi​​cator的按钮,其样式与普通按钮相同？

import UIKit

class ViewController: UIViewController {

    let activityIndicatorView = UIActivityIndicatorView(style: .gray)
    let button = UIButton(type: .system)

    override func viewDidLoad() {
        super.viewDidLoad()

        // 创建UIButton
        button.frame = CGRect(x: 0, y: 0, width: 50, height: 30)
        button.setTitle("按钮", for: .normal)
        button.addTarget(self, action: #selector(buttonClicked), for: .touchUpInside)

        // 创建UIActivityIndicatorView
        activityIndicatorView.frame = CGRect(x: 0, y: 0, width: 20, height: 20)
        activityIndicatorView.center = CGPoint(x: button.bounds.width/2, y: button.bounds.height/2)
        button.addSubview(activityIndicatorView)

        // 添加UIButton到导航栏
        let barButton = UIBarButtonItem(customView: button)
        self.navigationItem.rightBarButtonItem = barButton
    }

    @objc func buttonClicked() {
        // 控制UIActivityIndicatorView的显示和隐藏
        if activityIndicatorView.isAnimating {
            activityIndicatorView.stopAnimating()
        } else {
            activityIndicatorView.startAnimating()
        }
    }
}