Swift saving and retrieving custom object from UserDefaults

Question

I have this in Playground using Swift 3, Xcode 8.0:

import Foundation
class Person: NSObject, NSCoding {
    var name: String
    var age: Int
    init(name: String, age: Int) {
        self.name = name
        self.age = age
    }
    required convenience init(coder aDecoder: NSCoder) {
        let name = aDecoder.decodeObject(forKey: "name") as! String
        let age = aDecoder.decodeObject(forKey: "age") as! Int
        self.init(
            name: name,
            age: age
        )
    }
    func encode(with aCoder: NSCoder) {
        aCoder.encode(name, forKey: "name")
        aCoder.encode(age, forKey: "age")
    }
}

---

create array of Person

let newPerson = Person(name: "Joe", age: 10)
var people = [Person]()
people.append(newPerson)

---

encode the array

let encodedData = NSKeyedArchiver.archivedData(withRootObject: people)
print("encodedData: \(encodedData))")

---

save to userDefaults

let userDefaults: UserDefaults = UserDefaults.standard()
userDefaults.set(encodedData, forKey: "people")
userDefaults.synchronize()

---

check

print("saved object: \(userDefaults.object(forKey: "people"))")

---

retreive from userDefaults

if let data = userDefaults.object(forKey: "people") {
    let myPeopleList = NSKeyedUnarchiver.unarchiveObject(with: data as! Data)
    print("myPeopleList: \(myPeopleList)")
}else{
    print("There is an issue")
}

---

just check the archived data

if let myPeopleList = NSKeyedUnarchiver.unarchiveObject(with: encodedData){
   print("myPeopleList: \(myPeopleList)")
}else{
   print("There is an issue")
}

I'm not able to correctly save the data object to userDefaults, and in addition, the check at the bottom creates the error:

Fatal error: Unexpectedly found nil while unwrapping an Optional value

The "check" line also shows the saved object is nil. Is this an error in my object's NSCoder?

Answer 1

Swift 4 or later

You can once again save/test your values in a Playground

---

UserDefaults need to be tested in a real project. Note: No need to force synchronize. If you want to test the coding/decoding in a playground you can save the data to a plist file in the document directory using the keyed archiver. You need also to fix some issues in your class:

---

class Person: NSObject, NSCoding {
    let name: String
    let age: Int
    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")
    }
}

---

Testing:

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()

        do {
            // setting a value for a key
            let newPerson = Person(name: "Joe", age: 10)
            var people = [Person]()
            people.append(newPerson)
            let encodedData = try NSKeyedArchiver.archivedData(withRootObject: people, requiringSecureCoding: false)
            UserDefaults.standard.set(encodedData, forKey: "people")
            // retrieving a value for a key
            if let data = UserDefaults.standard.data(forKey: "people"),
                let myPeopleList = try NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(data) as? [Person] {
                myPeopleList.forEach({print($0.name, $0.age)})  // Joe 10
            }                    
        } catch {
            print(error)
        }
        
    }
}

Answer 2

let age = aDecoder.decodeObject(forKey: "age") as! Int

This has been changed for Swift 3; this no longer works for value types. The correct syntax is now:

let age = aDecoder.decodeInteger(forKey: "age")

There are associated decode...() functions for various different types:

let myBool = aDecoder.decodeBoolean(forKey: "myStoredBool")
let myFloat = aDecoder.decodeFloat(forKey: "myStoredFloat")

Edit: Full list of all possible decodeXXX functions in Swift 3

Edit:

Another important note: If you have previously saved data that was encoded with an older version of Swift, those values must be decoded using decodeObject(), however once you re-encode the data using encode(...) it can no longer be decoded with decodeObject() if it's a value type. Therefore Markus Wyss's answer will allow you to handle the case where the data was encoded using either Swift version:

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

Answer 3

In Swift 4:

You can use Codable to save and retrieve custom object from the Userdefaults. If you're doing it frequently then you can add as extension and use it like below.

extension UserDefaults {

   func save<T:Encodable>(customObject object: T, inKey key: String) {
       let encoder = JSONEncoder()
       if let encoded = try? encoder.encode(object) {
           self.set(encoded, forKey: key)
       }
   }

   func retrieve<T:Decodable>(object type:T.Type, fromKey key: String) -> T? {
       if let data = self.data(forKey: key) {
           let decoder = JSONDecoder()
           if let object = try? decoder.decode(type, from: data) {
               return object
           }else {
               print("Couldnt decode object")
               return nil
           }
       }else {
           print("Couldnt find key")
           return nil
       }
   }

}

Your Class must follow Codable. Its just a typealias for both Encodable & Decodable Protocol.

class UpdateProfile: Codable {
  //Your stuffs
}

Usage:

let updateProfile = UpdateProfile()

//To save the object
UserDefaults.standard.save(customObject: updateProfile, inKey: "YourKey")

//To retrieve the saved object
let obj = UserDefaults.standard.retrieve(object: UpdateProfile.self, fromKey: "YourKey")

For more Encoding and Decoding Custom types, Please go through the Apple's documentation.

Answer 4

Try this:

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

Answer 5

In Swift 5, I would use a property wrapper to simply the code:

/// A type that adds an interface to use the user’s defaults with codable types
///
/// Example:
/// ```
/// @UserDefaultCodable(key: "nameKey", defaultValue: "Root") var name: String
/// ```
/// Adding the attribute @UserDefaultCodable the property works reading and writing from user's defaults
/// with any codable type
///
@propertyWrapper public struct UserDefaultCodable<T: Codable> {
    private let key: String
    private let defaultValue: T

    /// Initialize the key and the default value.
    public init(key: String, defaultValue: T) {
        self.key = key
        self.defaultValue = defaultValue
    }

    public var wrappedValue: T {
        get {
            // Read value from UserDefaults
            guard let data = UserDefaults.standard.object(forKey: key) as? Data else {
                // Return defaultValue when no data in UserDefaults
                return defaultValue
            }

            // Convert data to the desire data type
            let value = try? JSONDecoder().decode(T.self, from: data)
            return value ?? defaultValue
        }
        set {
            // Convert newValue to data
            let data = try? JSONEncoder().encode(newValue)

            // Set value to UserDefaults
            UserDefaults.standard.set(data, forKey: key)
        }
    }
}