NSKeyedArchiver does not work in Swift 3 (Xcode 8)

Question

I have migrated my project to Swift 3 and NSKeyedArchiver does not work. I actually have a runtime error when trying to decode object like this:

let startDayTime = aDecoder.decodeObject(forKey: Key.startDayTime) as! Int

It worked perfectly in Swift 2.2 in Xcode 7.3. Has anybody else faced such troubles?

P.S. I have this error on both Simulator and Device.

Answer 1

It appears that this only happens on the Swift 2 to Swift 3 update boundary when a NSData blob archived with a NSKeyedArchiver in Swift 2 is opened with a NSKeyedUnarchiver in Swift 3. My guess is that on Swift 2, the Bool and Int are encoded as NSNumber, but in Swift 3, they are encoded as raw Bool and Int types. I believe the following test supports this claim:

This works in Swift 3 to unarchive a Bool encoded in Swift 2, but returns nil if the Bool was encoded in Swift 3:

let visible = aDecoder.decodeObject(forKey: "visible") as? Bool

This works in Swift 3 to unarchive a Bool encoded in Swift 3, but crashes if the Bool was encoded in Swift 2:

let visible = aDecoder.decodeBool(forKey: "visible")

My solution is:

let visible = aDecoder.decodeObject(forKey: "visible") as? Bool ?? aDecoder.decodeBool(forKey: "visible")

Answer 2

I solved this problem by using:

decodeInteger(forKey key: String)

instead of:

decodeObject(forKey key: String)

For some reason AnyObject does not cast to Integer in Swift 3, though it did in Swift 2.2

Answer 3

Here is solution:

class Person: NSObject, NSCoding {
    let name: String
    let age: Int
    required init(name: String, age: Int) {
        self.name = name
        self.age = age
    }
    required init(coder decoder: NSCoder) {
        self.name = decoder.decodeObject(forKey: "name") as? String ?? ""
        self.age = decoder.decodeInteger(forKey: "age")
    }

    func encode(with coder: NSCoder) {
        coder.encode(name, forKey: "name")
        coder.encode(age, forKey: "age")
    }
}

How to use:

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        let newPerson = Person(name: "Joe", age: 10)
        var people = [Person]()
        people.append(newPerson)
        let encodedData = NSKeyedArchiver.archivedData(withRootObject: people)
        UserDefaults.standard().set(encodedData, forKey: "people")
        if let data = UserDefaults.standard().data(forKey: "people"),
            myPeopleList = NSKeyedUnarchiver.unarchiveObject(with: data) as? [Person] {
            myPeopleList.forEach({print( $0.name, $0.age)})  // Joe 10
        } else {
            print("There is an issue")
        }
    }
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
}

Reference: Swift 3 saving and retrieving custom object from userDefaults

Answer 4

Swift 3:

I adopt the double question mark (??) method and it work like a charm in only one line.

If val is not nil than it is unwrapped and the value returned. If it is nil then aDecoder.decodeInteger(forKey: "val") returned:

self.val = aDecoder.decodeObject(forKey: "val") as? Int ?? aDecoder.decodeInteger(forKey: "val")