ViewController参考未维护

Question

我有一个服务类AuthManager，它具有如下方法：

public func logoutAuth(from viewController: UIViewController, completion:((_ result: Bool) -> Void)? = nil) {
        let logoutString = "\(self.oAuthBaseServerURL)/logout.jsp"
        // Present the Sign Off ViewController
        if let logoutURL = URL(string: logoutString) {
            let logoutController = SFSafariViewController(url: logoutURL)
            let logoutDelegate = SFSafariViewDelegate(completion: completion)
            logoutController.delegate = logoutDelegate
            viewController.present(logoutController, animated: true, completion: nil)
        }
    }

我在视图控制器中从它的一个实例（处于全局状态的单个）调用该服务，如下所示：

GlobalState.AUTHMANAGER().logoutAuth(from: self, completion: self.completeLogout)

但是，我遇到此错误：

 [Warning] Attempting to load the view of a view controller while it is deallocating is not allowed and may result in undefined behavior (<SFSafariViewController: 0x7ff9b1060800>)

我不确定为什么这样做分配得太早。我尝试将SFSafariViewController设置为实例变量，并改为在方法中分配它，这会产生相同的错误。