How to save json data on userdefaults in swift 4

Question

This is my model class

class UserRoot : Mappable {
    var success : Bool!
    var user : UserDetails!
    var error = ""

    required init?(map: Map) {

    }
    func mapping(map: Map) {
        success <- map["success"]
        user <- map["user"]
        error <- map["error"]

    }
}

after successfully login i want to save this data on user defaults so that when a user have to not give login credential again. Here is my code

class Default : NSObject{
    static func saveToSharedPrefs(user: UserDetails!) {
        let d = UserDefaults.standard
        if user != nil {
            d.set(Mapper().toJSONString(user, prettyPrint: false) , forKey: "USERDETAILS")
        } else {
            d.set(nil, forKey: "USERDETAILS")
        }
        d.synchronize()
    }
}

Answer 1

Make sure your model class is inherited from NSObject class otherwise it will crash at run time.

To store data:

let data = NSKeyedArchiver.archivedData(withRootObject: <Your model class>)
UserDefaults.standard.set(data, forKey: "userDetails")

To retrive and convert data back

if let data = UserDefaults.standard.value(forKey: "userDetails") as? Data {
    if let dict = NSKeyedUnarchiver.unarchiveObject(with: data) as? <Your model class> {
           print(dict)
     }
}

Answer 2

In swift 4 Better use JSONEncoder to encode your Swift object to JSON and JSONDecoder to decode your JSON to Swift object, Confirm Codable protocol to your Model class before encode and decode. You can follow this answer from stack overflow