删除存储在属性中的值

Question

我有点迷失并坚持下去并需要帮助。

假设我有两个视图控制器，在View Controller＃1中我有一个登录页面，用户通常通过VC＃1登录，而在View控制器＃2中，我有一个标签，我想显示用户名，在VC＃1中输入。

它对我有用，但是它显示了我输入的第一个用户名，而不是最新的用户名。所以我的问题是，如何清除输入到用户名的用户名，因此它不会存储超过1个。

@IBAction func btnLogin(sender: AnyObject)
{
    if (txtUsername.text == "")
    {
        //Show Error Message
        let alert = UIAlertView()
        alert.title = "Empty Field"
        alert.message = "Please enter your username"
        alert.addButtonWithTitle("Okay")
        alert.show()
    }
    else if (txtPassword.text == "")
    {
        //Show Error Message
        let alert = UIAlertView()
        alert.title = "Empty Field"
        alert.message = "Please enter your password"
        alert.addButtonWithTitle("Okay")
        alert.show()
    }
    else
    {


        let appDel:AppDelegate = (UIApplication.sharedApplication().delegate as! AppDelegate)
        let context: NSManagedObjectContext = appDel.managedObjectContext
        let request = NSFetchRequest(entityName: "Members")

        request.returnsObjectsAsFaults = false
        request.predicate = NSPredicate(format: "username = %@", txtUsername.text!)


        let results:NSArray =  try! context.executeFetchRequest(request)

        if results.count > 0
        {
            let res = results[0] as! NSManagedObject

            txtUsername.text = res.valueForKey("username") as? String
            txtPassword.text = res.valueForKey("password") as? String

            txtUsername.text = ""
            txtPassword.text = ""

            //Transfers you to another view controller
            let secondViewController = self.storyboard!.instantiateViewControllerWithIdentifier("HomePageViewController") as UIViewController

            self.presentViewController(secondViewController, animated: true, completion: nil)

        }
        else
        {
            //Show Error Message
            let alert = UIAlertView()
            alert.title = "No such user"
            alert.message = "User does not exist"
            alert.addButtonWithTitle("Okay")
            alert.show()
        }

    }



}

这是用于在另一个视图控制器中显示用户名的代码（仅1行），其中＆＃34; lblUsername.text = res.valueForKey（＆＃34; username＆＃34;）为？串 ＆＃34;

override func viewDidLoad() {
    let appDel:AppDelegate = (UIApplication.sharedApplication().delegate as! AppDelegate)
    let context: NSManagedObjectContext = appDel.managedObjectContext
    let request = NSFetchRequest(entityName: "Members")

    request.returnsObjectsAsFaults = false


    let results:NSArray =  try! context.executeFetchRequest(request)


    index = Int(arc4random_uniform(6))
    let res = results[0] as! NSManagedObject

    super.viewDidLoad()
    circularImage(imageView1)
    lblUsername.text = res.valueForKey("username") as? String

    //Code to animate images
    imageView1.animationImages = [
        UIImage(named: Data.images[0])!,
        UIImage(named: Data.images[1])!,
        UIImage(named: Data.images[2])!,
        UIImage(named: Data.images[3])!,
        UIImage(named: Data.images[4])!,
        UIImage(named: Data.images[5])!
    ]

    imageView1.animationDuration = 15
    imageView1.startAnimating()


}