快速定制segue条件

我正在尝试根据用户登录信息是否正确来有条件地执行segue.

我从登录View Controller到新的导航控制器有一个模态segue.

我已经尝试过几乎所有我遇到过的建议,似乎没有任何工作.使用Sift和Xcode 6.

import UIKit

import AudioToolbox

class ViewController: UIViewController {

   @IBOutlet weak var usernameTextField: UITextField!

   @IBOutlet weak var passwordTextField: UITextField!

   @IBOutlet weak var incorrectCredentialLabel: UILabel!

   @IBAction func loginAction(sender: UIButton) {

       var username = "test"
       var password = "code"

       println("Username: " + usernameTextField.text)
       println("Password: " + passwordTextField.text)

       if usernameTextField.text == username &&
          passwordTextField.text == password {

          usernameTextField.resignFirstResponder()
          passwordTextField.resignFirstResponder()

          println("Login Status: success")

       self.shouldPerformSegueWithIdentifier("loginSegue", sender: nil)

    } else {

         usernameTextField.resignFirstResponder()
         passwordTextField.resignFirstResponder()

         AudioServicesPlayAlertSound(1352)
        /*AudioServicesPlayAlertSound(kSystemSoundID_Vibrate)*/

         incorrectCredentialLabel.text = "username or password is incorrect"
         incorrectCredentialLabel.textColor = UIColor.redColor()

         println("Login Status: failed")
    }
}

 override func viewDidLoad() {
     super.viewDidLoad()
     // Do any additional setup after loading the view, typically from a nib.
 }

 override func didReceiveMemoryWarning() {
     super.didReceiveMemoryWarning()
     // Dispose of any resources that can be recreated.
 }

}

这对我有用.两个UITextFields和一个UIButton以及从VC到VC2的模态segue：

import UIKit

class ViewController: UIViewController, UITextFieldDelegate {

    let userName = "John"
    let passCode = "123"

    @IBOutlet weak var Name: UITextField!

    @IBOutlet weak var Pass: UITextField!
    @IBAction func tapButton(sender: UIButton) {

        if self.Name.text == "John" && self.Pass.text == "123" {

         performSegueWithIdentifier("nextView", sender: self)
        }
    }

    //ViewController lifecycle
    override func viewDidLoad() {
        super.viewDidLoad()

        self.Name.delegate = self
        self.Pass.delegate = self

    }
}