Swift 3 saving and retrieving custom object from u

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

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 2

Try this:

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

Answer 3

Swift 4 Note

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

---

Swift 3

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()
        // setting a value for a key
        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")

        // retrieving a value for a key
        if let data = UserDefaults.standard.data(forKey: "people"),
            let myPeopleList = NSKeyedUnarchiver.unarchiveObject(with: data) as? [Person] {
            myPeopleList.forEach({print( $0.name, $0.age)})  // Joe 10
        } else {
            print("There is an issue")
        }
    }
}