UIAlertController标题和消息未出现

我正在使用此代码：

let alertController = UIAlertController(title: "Default AlertController", message: "A standard alert", preferredStyle: .Alert) let cancelAction = UIAlertAction(title: "Cancel", style: .Cancel) { (action:UIAlertAction!) in print("you have pressed the Cancel button"); } alertController.addAction(cancelAction) let OKAction = UIAlertAction(title: "OK", style: .Default) { (action:UIAlertAction!) in print("you have pressed OK button"); } alertController.addAction(OKAction) self.presentViewController(alertController, animated: true, completion:nil) 

这就是它的样子：

以下是演示文稿的代码。 我正在检查CloudKit的auth状态，然后在出现错误时显示警报：

 dispatch_async(dispatch_get_main_queue(), { self.activityIndicator.stopAnimating() guard let user = user where succeeded && error == nil else { if let error = error { switch error { default: let alertController = UIAlertController(title: "Default AlertController", message: "A standard alert", preferredStyle: .Alert) let cancelAction = UIAlertAction(title: "Cancel", style: .Cancel) { (action:UIAlertAction!) in print("you have pressed the Cancel button"); } alertController.addAction(cancelAction) let OKAction = UIAlertAction(title: "OK", style: .Default) { (action:UIAlertAction!) in print("you have pressed OK button"); } alertController.addAction(OKAction) self.presentViewController(alertController, animated: true, completion:nil) } } return } })