使用Facebook令牌调用用户？.reauthenticate时没有输出

Question

我尝试检查Firebase中是否已存在经过身份验证的用户。我发现user?.reauthenticate可以解决这个问题，但不幸的是，当我运行它时，它会卡在reauthenticate方法上。我在控制台中看不到任何错误消息。我在iOS模拟器上运行代码。

有人可以帮我这个吗？难道我做错了什么？感谢

    func loginButton(_ loginButton: FBSDKLoginButton!, didCompleteWith result: FBSDKLoginManagerLoginResult!, error: Error!) {


    self.loginButton.isHidden = true
        self.loadspinnerAIV.startAnimating()

    if(error != nil){
        //handle errors
        self.loginButton.isHidden = false
        self.loadspinnerAIV.stopAnimating()
    }else if(result.isCancelled){
        //handle cancel event
        self.loginButton.isHidden = false
        self.loadspinnerAIV.stopAnimating()
    }else{
        let credential = FIRFacebookAuthProvider.credential(withAccessToken: FBSDKAccessToken.current().tokenString)

        let user = FIRAuth.auth()?.currentUser

        // Prompt the user to re-provide their sign-in credentials
        user?.reauthenticate(with: credential) { error in
            if let error = error {
                print ("User does not exist")
                FIRAuth.auth()?.signIn(with: credential) { (user, error) in}
            } else {
                print ("User does exist")
                self.performSegue(withIdentifier: "showHome", sender: self)

            }
        }
    }
}.