How to save custom objects that implements Codable - ios

Question

It's now easier with Swift 4 to encode / decode to and from JSON or Properties list.
But I can't find how to encode to Data using Codable, without using Objective-C methods initWithCoder and encodeWithCoder.
Considering this simple class:
struct Question: Codable {
var title: String
var answer: Int
var question: Int
}
How can I encode it to Data using CodingKeys and not initWithCoder and encodeWithCoder?
EDIT:
I also need to be able to deserialize objects previously saved in userdefaults using NSKeyedArchiver.

Answer 1

Well, you no longer need NSKeyedArchiver.
Try this:
let questionObj = Question(title: "WWDC, 2017", answer: 1,question:1)
let encoder = JSONEncoder()
if let encoded = try? encoder.encode(questionObj) {
UserDefaults.standard.set(encoded, forKey: "K_Question")
}
let decoder = JSONDecoder()
if let questionData = UserDefaults.standard.data(forKey: "K_Question"),
let question = try? decoder.decode(Question.self, from: questionData) {
print(question.title)
print(question.answer)
print(question.question)
}

Answer 2

Swift 5: a great simple extension for UserDefaults:
extension UserDefaults {
func save<T: Codable>(_ object: T, forKey key: String) {
let encoder = JSONEncoder()
if let encodedObject = try? encoder.encode(object) {
UserDefaults.standard.set(encodedObject, forKey: key)
UserDefaults.standard.synchronize()
}
}
func getObject<T: Codable>(forKey key: String) -> T? {
if let object = UserDefaults.standard.object(forKey: key) as? Data {
let decoder = JSONDecoder()
if let decodedObject = try? decoder.decode(T.self, from: object) {
return decodedObject
}
}
return nil
}
}
Usage
save
UserDefaults.standard.save(currentUser, forKey: "currentUser")
get
let user: User? = UserDefaults.standard.getObject(forKey: "currentUser")

Answer 3

Well it can be achieved via JSONEncoder and JSONDecoder.
struct Question: Codable {
var title: String
var answer: Int
var question: Int
}
let questionObj = Question(title: "Swift", answer: "Open Source",question:1)
let encoder = JSONEncoder()
if let encoded = try? encoder.encode(questionObj) {
if let json = String(data: encoded, encoding: .utf8) {
print(json)
}
let decoder = JSONDecoder()
if let decoded = try? decoder.decode(Question.self, from: encoded) {
print(decoded)
}
}

Answer 4

struct Question: Codable {
var title: String
var answer: Int
var question: Int
}
class UserDefaults_Question {
static let key = "myapp.trick.question"
static var value: UserDefaults_Question? {
get {
guard let data = UserDefaults.standard.data(forKey: key) else {
print("no model for key: \(key)")
return nil
}
guard let model = try? JSONDecoder().decode(UserDefaults_Question.self, from: data) else {
print("failed to decode model for key: \(key)")
return nil
}
print("did load model for key: \(key)")
return model
}
set {
guard let value = newValue, let data: Data = try? JSONEncoder().encode(value) else {
print("removing model for key: \(key)")
UserDefaults.standard.removeObject(forKey: key)
return
}
print("inserting model for key: \(key)")
UserDefaults.standard.set(data, forKey: key)
}
}
}
UserDefaults_Question.value = Question(title: "Next President", answer: 666, question: -1)