How to save object into UserDefaults or keychain – Swift 3 – Shopify

You definitely can store the whole object in your UserDefaults or a Keychain, no problem. The trick is to make it conform to the NSCoding protocol, then use NSKeyedArchiver and NSKeyedUnarchiver to convert it to and from a Data object that can be stored. Don’t worry, it sounds more complicated than it is.

Conforming to NSCoding

Presumably your BUYCustomerToken class is already a descendant of NSObject, so you’re halfway there. You just need to add a couple of methods to allow your custom class to be encoded (turned into Data) and decoded automatically from an NSCoder. Specifically these are: encode(with coder: NSCoder) and init(coder aDecoder:NSCoder). You then use the coder’s various encode() and decode() functions to make these work. encode() and decode() work on any object that supports NSCoding, which includes NSNumber, String, and Date, so that makes your job here pretty easy. A finished codable class will look like this:

class BUYCustomerToken : NSObject, NSCoding {

    var customerID: NSNumber!
    var accessToken: String!
    var expiry: Date!

    override init() {
    }

    convenience init(customerID: NSNumber, accessToken: String, expiry: Date) {
        self.init()
        self.customerID = customerID
        self.accessToken = accessToken
        self.expiry = expiry
    }

    required init(coder aDecoder: NSCoder) {
        customerID = aDecoder.decodeObject(forKey: "customerID") as! NSNumber
        accessToken = aDecoder.decodeObject(forKey: "accessToken") as! String
        expiry = aDecoder.decodeObject(forKey: "expiry") as! Date
    }

    func encode(with aCoder: NSCoder) {
        aCoder.encode(customerID, forKey: "customerID")
        aCoder.encode(accessToken, forKey: "accessToken")
        aCoder.encode(expiry, forKey: "expiry")
    }

    override var description: String {
        return "ID: (customerID!), Token: "(accessToken!)", Expires: (expiry!)"
    }
}

You can add in your own custom methods, of course. The description is not strictly necessary, but convenient for testing.

Storing and Retrieving from UserDefaults

Now that your class supports NSCoding, you can archive it and store it, then retrieve it.

To store it, you start by archiving it (converting it to a Data object) using NSKeyedArchiver.archivedData(withRootObject). This works because your class is NSCoding compliant. Once you get a Data object, you can store that in UserDefaults using set(value, forKey).

When you want to retrieve it, you do it the other way: first fetch a Data object from UserDefaults using data(forKey), then turn it back into an object using NSKeyedUnarchiver.unarchiveObject(with), and finally cast it to your custom class.

Here’s a bit of code that attempts to load a BUYCustomerToken from UserDefaults. If it succeeds, it prints the description; if it fails, it creates a new token and stores it. Put this code in the viewDidLoad() of your initial UIViewController to see it in action:

if let customerTokenData = UserDefaults.standard.data(forKey: "myToken") {
    let customerToken = NSKeyedUnarchiver.unarchiveObject(with: customerTokenData) as! BUYCustomerToken
    print(customerToken)
} else {
    print("No token stored. Launch again to see token.")
    let customerToken = BUYCustomerToken(customerID: 999, accessToken: "some token", expiry: Date())
    let tokenData = NSKeyedArchiver.archivedData(withRootObject: customerToken)
    UserDefaults.standard.set(tokenData, forKey: "myToken")
}

The first time you run it there’s no stored token, so the output is:

No token stored. Launch again to see token.

The second time, it will find the stored token and output its description:

ID: 999, Token: “some token”, Expires: 2017-05-31 21:27:25 +0000