alertController没有出现在Swift中

Question

我在viewDidAppear中调用该方法，但是alertController永远不会出现，似乎没有理由。

func genderAlert()
    {
        let alertController = UIAlertController(title: "Quick Question:", message: "How would you describe yourself?", preferredStyle: UIAlertControllerStyle.alert)
        let okAction = UIAlertAction(title: "Party Animal", style: UIAlertActionStyle.default) {
            UIAlertAction in
            print("Party animal Pressed")
        }
        let cancelAction = UIAlertAction(title: "Study Buddy", style: UIAlertActionStyle.default) {
            UIAlertAction in
            print("Study Buddy Pressed")
        }
        alertController.addAction(okAction)
        alertController.addAction(cancelAction)
        self.present(alertController, animated: true, completion: nil)
    }