Cannot archive custom class object with NSKeyedArchiver

Question

I am trying to perform a simple archive operation to my custom class Car . I followed Apple documentation and made it conform to Codable protocol:

class Car: NSObject, Codable {
    var name: String!

    init(name:String) {
        self.name = name
    }
}

And i want to archive it like:

let car = Car(name: "Ferrari")
let data = NSKeyedArchiver.archivedData(withRootObject: car)

But in the second line the app crashes and i get the following error:

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[_TtCC11Testing6MainVC3Car encodeWithCoder:]: unrecognized selector sent to instance 0x1c4035880' libc++abi.dylib: terminating with uncaught exception of type NSException

I've searched SO but i only found solutions for structs, whereas i am using a class. What can i do?

Answer 1

The NSKeyedArchiver.archivedData(withRootObject:) method should be used on objects that conform to NSCoding NOT Codable/Encodable/Decodable .

If you want your object to implement the Codable protocol you can use the JSONEncoder and JSONDecoder like below to achieve the same thing:

let car = Car(name: "Ferrari")
if let encodedCarData: Data = try? JSONEncoder().encode(car) {
    let decodedCar = try? JSONDecoder().decode(Car.self, from: encodedCarData)
}

If you wish to use the NSKeyedArchiver instead, you can use the example below:

class Car: NSObject, NSSecureCoding {

    static var supportsSecureCoding: Bool { return true }

    var name: String

    init(name: String) {
        self.name = name
    }

    required init?(coder aDecoder: NSCoder) {
        guard let name = aDecoder.decodeObject(forKey: "name") as? String else { return nil }
        self.name = name
    }

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

}

let car = Car(name: "Ferrari")
if let encodedCarData = 
    try? NSKeyedArchiver.archivedData(withRootObject: car, 
                                      requiringSecureCoding: false) {
    let decodedCar = 
        try NSKeyedUnarchiver.unarchivedObject(ofClass: Car.self, 
                                               from: encodedCarData)
}

You should also note, archivedData(withRootObject:) was deprecated in iOS 12.0 and you should use +archivedDataWithRootObject:requiringSecureCoding:error: instead.