Chapter 5. Data Storage

Games are apps, and apps run on data. Whether it’s just resources that your game loads or saved-game files that you need to store, your game will eventually need to work with data stored on the flash chips that make up the storage subsystems present on all iOS devices.

In this chapter, you’ll learn how to convert objects into saveable data, how to work with iCloud, how to load resources without freezing up the rest of the game, and more.

Saving the State of Your Game


You want game objects to be able to store their state, so that it can be loaded from disk.


Make your objects conform to the NSCoding protocol, and then implement encodeWithCoder and init(coder:), like so:

class Monster: NSObject, NSCoding {

    // Game data
    var hitPoints = 0
    var name = "GameObject"

    // Initializer used when creating a brand new object
    override init() {


    // Initializer used when loading the object from data
    required init(coder aDecoder: NSCoder) {

        self.hitPoints = aDecoder.decodeIntegerForKey("hitPoints")

        // Attempt to get the object with key "name" as a string;
        // if we can't convert it to a string or it doesn't exist,
        // fall back to "No Name" = aDecoder.decodeObjectForKey("name") as? String ?? "No Name"

    func encodeWithCoder(aCoder: NSCoder) {

        aCoder.encodeObject(, forKey: "name")
        aCoder.encodeInteger(self.hitPoints, forKey: "hitPoints")



When you want to store this information into an NSData object, for saving to disk or somewhere else, you use ...

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