Changing from NSUserDefaults to NSCoding

Question

I'm trying to create my first sprite kit swift game, and I have my game data working using nsuserdefaults. I want to make it more safe so I'm attempting to transition to NSCoding, but nothing I've found online has helped me completely and has just confused me (so sorry if an answer already exists, I probably already looked at it and wasn't able to understand.)

This is my GameState class:

class GameState {
var score: Int
var highScore: Int
var stars: Int
var sound: Bool
var carType: Int
var xSize: Double
var ySize: Double
var gameOver: Bool

class var sharedInstance: GameState {
    struct Singleton {
        static let instance = GameState()
    }

    return Singleton.instance
}

init() {
    // Init
    score = 0
    highScore = 0
    stars = 0
    carType = 1
    sound = true
    xSize = 1
    ySize = 1
    gameOver = false

    // Load game state
    let defaults = NSUserDefaults.standardUserDefaults()

    highScore = defaults.integerForKey("highScore")
    stars = defaults.integerForKey("stars")
    sound = defaults.boolForKey("sound")
    carType = defaults.integerForKey("carType")
    xSize = defaults.doubleForKey("xSize")
    ySize = defaults.doubleForKey("ySize")
    gameOver = defaults.boolForKey("gameOver")
}


func saveState() {
    // Update highScore if the current score is greater
    highScore = max(score, highScore)

    // Store in user defaults
    let defaults = NSUserDefaults.standardUserDefaults()
    defaults.setInteger(highScore, forKey: "highScore")
    defaults.setInteger(stars, forKey: "stars")
    defaults.setBool(sound, forKey: "sound")
    defaults.setInteger(carType, forKey: "carType")
    defaults.setDouble(xSize, forKey: "xSize")
    defaults.setDouble(ySize, forKey: "ySize")
    defaults.setBool(gameOver, forKey: "gameOver")
    NSUserDefaults.standardUserDefaults().synchronize()
} }

and I save and load data in my other classes using:

GameState.sharedInstance.*****

How would I go about changing this to implement NSCoding and then load and save the data from other classes? Thanks.

Answer 1

The class you want to save has to conform to the NSCoding protocol and implement required init(coder aDecoder: NSCoder) and func encodeWithCoder(aCoder: NSCoder).

Here's a simplified example:

class GameState: NSObject, NSCoding {

    var score: Int?
    var gameOver: Bool?

    init(score: Int, gameOver: Bool) {
        super.init()
        self.score = score
        self.gameOver = gameOver
    }

    required init(coder aDecoder: NSCoder) {
        self.score = aDecoder.decodeObjectForKey("score") as? Int
        self.gameOver = aDecoder.decodeObjectForKey("gameOver") as? Bool
    }

    func encodeWithCoder(aCoder: NSCoder) {
        aCoder.encodeObject(self.score, forKey: "score")
        aCoder.encodeObject(self.gameOver, forKey: "gameOver")
    }

}

let myGameState = GameState(score: 42, gameOver: true)

Then you can use NSKeyedArchiver and NSKeyedUnarchiver, for example in the AppDelegate, to save and load your object as data:

func applicationWillTerminate(aNotification: NSNotification) {
    NSKeyedArchiver.archiveRootObject(myGameState, toFile: "a/file/path")
}

func applicationDidFinishLaunching(aNotification: NSNotification) {
    if let data = NSKeyedUnarchiver.unarchiveObjectWithFile("a/file/path") as? GameState {
        myGameState = data
    }
}