在segue期间提供alertviewcontroller

Question

我有一个帮助方法，在我的实际视图控制器上提示alertviewcontroller。但是，如果这发生在segue期间。我的segue被取消了。有什么想法吗？

    AlamoHelper.request(.POST, url: AppDelegate.kbaseUrl + "users/signin", parameters: ["email": String(emailTextField.text!), "password": String(passwordTextField.text!)])
        .responseJSON {
            response in
            switch (response.result) {
            case .Success:
                var json = JSON(response.result.value!)
                if (json["status"] != 200){
                    AppDelegate.removeCookies()
                    AppDelegate.isLoggedIn = false
                } else {
                    self.performSegueWithIdentifier("showTabBarController", sender: self)
                    self.emailTextField.text = ""
                    self.passwordTextField.text = ""
                    self.appDelegate.storeCookies()
                    AppDelegate.isLoggedIn = true
                    self.addDeviceToken()
                }
                break

            case .Failure:
                break
            }
    }

在我的助手中，我显示警报控制器的部分是这个

    if json["status"].intValue == 500 {
                    let alert = UIAlertController(title: "Unknown error", message: "Please try again later. If problem persists, please contact Offpeak support", preferredStyle: .Alert)
                    let okAction = UIAlertAction(title: "Ok", style: .Cancel, handler: nil)
                    alert.addAction(okAction)

                    AlamoHelper.getCurrentViewController().presentViewController(alert, animated: true, completion: nil)
                }