ios - NSUserDefaults 在 View 之间被删除

Question

当按下按钮时，我设置了一个 NSUserDefaults 值，但是当 View 转换时，该值被取消设置，并且什么也没有返回。
代码:
按钮代码

func chooseFriend(sender: UIButton) {
        let requestIndex = sender.tag
        let friendChosen = self.friends.objectAtIndex(requestIndex) as! String
        NSUserDefaults.standardUserDefaults().setObject(friendChosen, forKey: "usernameToMessageWith")
        NSUserDefaults.standardUserDefaults().synchronize()
        print(">>\(NSUserDefaults.standardUserDefaults().stringForKey("usernameToMessageWith")! as String)")
        self.performSegueWithIdentifier("toChat", sender: self)
    }

下一个查看代码

override func viewDidLoad() {
        super.viewDidLoad()
        print("TRANSITIONED")
        let receivedUsername = NSUserDefaults.standardUserDefaults().stringForKey("usernameToMessageWith")! as String
        print("RECEIVED USERNAME:\(receivedUsername)")
        refreshTable()
        let swipe: UISwipeGestureRecognizer = UISwipeGestureRecognizer(target: self, action: "dismissKeyboard")
        swipe.direction = UISwipeGestureRecognizerDirection.Down
        self.view.addGestureRecognizer(swipe)
        NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("keyboardWillShow:"), name: UIKeyboardWillShowNotification, object: nil)
        NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("keyboardWillHide:"), name: UIKeyboardWillHideNotification, object: nil)
        testLabel.text = ""
        self.messages.addObject("Loading......")
    }

输出:

TRANSITIONED
RECEIVED USERNAME:

Answer 1

我已经使用您的代码进行了测试，没有发现 NSUserDefaults 存在问题

NSUserDefaults.standardUserDefaults().setObject("Vien", forKey: "usernameToMessageWith")
    NSUserDefaults.standardUserDefaults().synchronize()

和:

let receivedUsername = NSUserDefaults.standardUserDefaults().stringForKey("usernameToMessageWith")! as String
    print("RECEIVED USERNAME:\(receivedUsername)")

和日志:

RECEIVED USERNAME:Vien

所以我认为这个问题出在你的chooseFriend上。您应该检查此行代码:

let friendChosen = self.friends.objectAtIndex(requestIndex) as! String