UIAlertController not displayed

Question

我有一个警报控制器，应该在用户在文本字段中输入不正确数量的字符后出现。警报控制器根本没有出现。 W

func usernameFieldCharacters() { 
    let alertController = UIAlertController(title: "Alert", message: "Five characters or more is required in all fields" , preferredStyle: UIAlertControllerStyle.Alert) 

    let okAction = UIAlertAction(title: "OK", style: .Default) { 

    action -> Void in // Does not do anything 
    } 

    alertController.addAction(okAction) // adds the OK button to 
    // to alert controller 

    let allowedChars = 5 // character amount has to be equal or greater in each field 
    let usernameCount = theUsernameField.text?.characters.count 

    if usernameCount < allowedChars { 
     self.presentViewController(alertController, animated: true, completion: nil) 
    } else { 
     alertController.viewDidAppear(false) 
    } 
} 

Answer 1

以上代码正常工作。 而alertController.viewDidAppear（假）是不需要

Answer 2

代码工作正确的，当u移动alertcontroller IE浏览器viewDidAppear法：

class ViewController: UIViewController { 

    override func viewDidAppear(animated: Bool) { 
    super.viewDidAppear(animated) 

    let allowedChars = 5 // character amount has to be equal or greater in each field 

    let usernameCount = theUsernameField.text?.characters.count 

    if usernameCount < allowedChars { 
     // Do any additional setup after loading the view, typically from a nib. 
     let alertController = UIAlertController(title: "Alert", message: "Five characters or more is required in all fields" , preferredStyle: UIAlertControllerStyle.Alert) 

     let okAction = UIAlertAction(title: "OK", style: .Default) { 

      action -> Void in // Does not do anything 
     } 

     alertController.addAction(okAction) // adds the OK button to 
     // to alert controller 

     self.present(alertController, animated: true, completion: nil) 
    }