如何在swift中防止UIViewController的多次推送？

class MyViewController: UIViewController {
    var isPushed = false

    override func viewDidLoad() {
        super.viewDidLoad()
        // 设置按钮点击事件
        let button = UIButton(type: .system)
        button.addTarget(self, action: #selector(pushAction), for: .touchUpInside)
    }

    @objc func pushAction() {
        if !isPushed {
            isPushed = true
            let nextViewController = NextViewController()
            navigationController?.pushViewController(nextViewController, animated: true)
        }
    }
}

class MyViewController: UIViewController, UINavigationControllerDelegate {
    override func viewDidLoad() {
        super.viewDidLoad()
        navigationController?.delegate = self
    }

    func navigationController(_ navigationController: UINavigationController, willShow viewController: UIViewController, animated: Bool) {
        if viewController == self {
            // 已经在当前视图控制器，不再推送
            navigationController?.delegate = nil
        }
    }
}

class MyViewController: UIViewController {
    var pushCompletionHandler: ((Bool) -> Void)?

    override func viewDidLoad() {
        super.viewDidLoad()
        let button = UIButton(type: .system)
        button.addTarget(self, action: #selector(pushAction), for: .touchUpInside)
    }

    @objc func pushAction() {
        if pushCompletionHandler == nil {
            pushCompletionHandler = { [weak self] (isPushed) in
                if isPushed {
                    let nextViewController = NextViewController()
                    self?.navigationController?.pushViewController(nextViewController, animated: true)
                }
            }
            pushCompletionHandler?(true)
        }
    }
}