Accessing A Variable In UserDefaults Swift 3 - swift

Question

This may seem like a basic question but I don't know the answer. In my app, you earn coins after every play of the game. Here is my code for earning coins and saving them
let defaultCoins = UserDefaults()
var coinNumber = defaultCoins.integer(forKey: "coinSaved")
coinNumber = coinNumber + score
defaultCoins.set(coinNumber, forKey: "coinSaved")
I would like to be able to access coinNumber from a different view controller and be able to use it. So maybe make a variable = coinNumber that I can access anywhere. I have a shop and would like to be able to purchase a new character when the user has 1000 coins but currently cant do that as I don't know how to access coinNumber from my shopViewController

Answer 1

Since you're saving the data to UserDefaults it doesn't seem like you should need to propagate it between view controllers - just use the defaults as your 'source of truth' for the correct value. Instead of saving it to a custom UserDefaults object, however, just save it to the standard one that is created for all iOS/OS X apps: UserDefaults.standard
Just read it from it whenever you need it the way you're already doing above. A couple things to note about this approach:
You can use Key/Value observing to detect changes to the value when other controllers modify it, but you'll need to be careful as KVO can be easy to crash if you forget to remove observers properly.
You should probably call synchronize on it which forces the changes you've made to disk. This will make sure that if your app is closed suddenly that you've secured the data.
UserDefaults is great for when you have less than 10 pieces of data you're wanting to save, like a highest score or a set of preferences (that's what it's made to do), but it's not great for large data structures. You should look into CoreData or KeyedArchiver for bigger stuff.
Pro-tip: Rather than using the loose string "coinSaved" over and over again, define a static constant somewhere, or use an enumeration of a string type to pre-define all your values once. Then you get code completion and avoid errors.
So, your code above would look more like:
In one view controller:
let defaultCoins = UserDefaults.standard
var coinNumber = defaultCoins.integer(forKey: "coinSaved")
coinNumber = coinNumber + score
defaultCoins.set(coinNumber, forKey: "coinSaved")
defaultCoins.synchronize()
Then, in another controller where you need to read it:
let defaultCoins = UserDefaults.standard
let coinNumber = defaultCoins.integer(forKey: "coinSaved")

Answer 2

Your main problem is that you are creating a new UserDefaults object whenever you try to access it, you should either use the UserDefaults.standard instance or create one with a specific identifier.
I would also suggest creating a singleton to manage the coins if you are going to use them in several view controllers, this is to save your time writing the same safety checks over and over (like making sure you can't spend more coins than you have)
It would look something like this:
class CoinManager {
static let shared = CoinManager()
private var _coins: UInt {
didSet {
UserDefaults.standard.set(_coins, forKey: "coinSaved")
}
}
var coins: UInt { return _coins }
private init() {
_coins = UInt(UserDefaults.standard.integer(forKey: "coinSaved"))
}
func spend(coins: UInt) -> Bool {
guard _coins > coins else { return false }
_coins -= coins
return true
}
func store(coins: UInt) -> UInt {
_coins += coins
return _coins
}
}
As you can see, other objects can only read the coins property but they can't modify it directly, if they want to modify it they have to use either spend or store. spend makes sure you can't spend more coins than you have.