NSUserDefaults key becomes nil when sent between view controllers - ios

Question

I need to send a username between two view controllers so that the second view controller knows who to send a message to. I have tried prepareForSegue, however I have found that the variable passed cannot be dynamically altered. I decided to use NSUserDefaults, which worked very well for the length of my development process. Today, it stopped working. I do not think I deleted anything or made an changes, but nevertheless NSUserDefaults is no longer reliably carrying the value between the two view controllers. Every once in a while (maybe 20% of the time?) the value will be correctly passed. The rest of the time, nothing comes through.Code:
Set key:
func chooseFriend(sender: UIButton) {
let requestIndex = sender.tag
let friendChosen = self.friends.objectAtIndex(requestIndex) as! String
NSUserDefaults.standardUserDefaults().setValue("thisisatest", forKey: "testKey")
NSUserDefaults.standardUserDefaults().synchronize()
self.performSegueWithIdentifier("toChat", sender: self)
}
Note: In the viewDidLoad I set testKey = ""
Retrieve key on new view controller:
override func viewDidLoad() {
super.viewDidLoad()
let theKey = NSUserDefaults.standardUserDefaults().valueForKey("testKey")
print("The Key: \(theKey)")
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......")
}
Every time, the default comes up empty: The Key: Optional()I can successfully print the default after setting it, however it disappears once I am segued to the next view controller...If anyone else has experienced this problem please let me know.Thanks
Randy's code:
func chooseFriend(sender: UIButton) {
let requestIndex = sender.tag
let friendChosen = self.friends.objectAtIndex(requestIndex) as! String
// Instantiate the second view controller via t's identifier in the storyboard
if let secondViewController = self.storyboard?.instantiateViewControllerWithIdentifier("ChatVC") as? chatViewController {
// Set the chosen friend
secondViewController.friendChosen = friendChosen
self.presentViewController(secondViewController, animated: true, completion: nil)
}
}
Added this to destinationviewcontroller:
var friendChosen: String!

Answer 1

The methods for NSUserDefaults are setObject:forKey: and objectForKey:, not setValue:forKey: (Or look at the special methods for specific object types, like setBool:forKey: or stringForKey: (I don't think there's a custom set method for strings.))
The methods with "value" in their names are KVC methods.
But, as Randy says, using your app's model is a better way to go, or passing the information directly to a property in the destination view controller in prepareForSegue. Using NSUserDefaults would not be my first, or my second, choice in this situation.

Answer 2

It looks like you're using storyboards already so it should be pretty easy to pass information using prepareForSegue like this.
class DestinationVC : UIViewController {
var destName : String!
override func viewWillAppear(animated: Bool) {
//configure UI with the destName
self.label.text = destName
}
}
class PresentingVC : UIViewController {
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if let destinationVC = segue.destinationViewController as? DestinationVC {
destinationVC.destName = "Some String to Pass"
}
}
}
As already mentioned NSUserDefaults is not ideal. You will also be loosing type safety and relying on string matching with keys in NSUserDefaults rather than autocompleting and compiler checking with a var on the destinationVC. It's also good practice to limit where your data is kept and where it could be altered. Storing something in NSUserDefaults when the use case is quite confined will make it more difficult to write focussed tests and make it vulnerable to change from any class anywhere in the app. It may be an edge case but starting a pattern like this in your app could expose you to all sorts of side effect bugs in the future.

Answer 3

Ultimately, this type of information should be passed from view controller to view controller in a model via a delegate. That would be the "appropriate" way to achieve this behavior via a true MVC pattern.
Having said that; I think the quickest fix for you would be not to use segues and to avoid NSUserDefaults all together.
Try the following...
func chooseFriend(sender: UIButton) {
let requestIndex = sender.tag
let friendChosen = self.friends.objectAtIndex(requestIndex) as! String
// Instantiate the second view controller via it's identifier in the storyboard
if let secondViewController = self.storyboard?.instantiateViewControllerWithIdentifier("SecondViewControllerIdentifier") as? SecondViewController {
// Set the chosen friend
secondViewController.friendChosen = friendChosen
self.presentViewController(secondViewController, animated: true, completion: nil)
}
}
And in the SecondViewController add the following property.
var friendChosen: String!
Please make sure the value is not nil prior to passing it to the destination view controller