How to save an array of classes in swift code

Question

I am trying to save an array of classes and here is my code so far:

The array:

var person1 = person(name: "Bob", age: 22)
var person2 = person(name: "John", age: 10)
var array = [person1, person2]

The custom class:

import UIKit

class person: NSObject, NSCoding {

    var name : String
    var age : Int

    init(name: String, age: Int) {
        self.name = name
        self.age = age
    }

    required init (coder aDecoder: NSCoder) {
        name = (aDecoder.decodeObject(forKey: "name") as? String)!
        age = (aDecoder.decodeObject(forKey: "age") as? Int)!
    }

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

To save the array:

let SavedData = NSKeyedArchiver.archivedData(withRootObject: array)

let defaults = UserDefaults.standard

defaults.set(SavedData, forKey: "myPeople")

To load the array:

let saveddata = UserDefaults.standard.object(forKey: "myPeople") as? Data

if saveddata != nil{
    array = (NSKeyedUnarchiver.unarchiveObject(with: saveddata!) as? [person])!
}

The error is at the line age = (aDecoder.decodeObject(forKey: "age") as? Int)!

Unknown class iewripple in Interface Builder file.

vadian · Accepted Answer · 2017-07-10 14:12:12Z

The error occurs because you are encoding an Int but decoding an object which fails.

There is a dedicated method decodeInteger(forKey.

Please conform to the naming convention that class names start with a capital letter and variable names start with a lowercase letter.

class Person: NSObject, NSCoding {

To solve the problem change the init(coder method to

required init(coder aDecoder: NSCoder) {
    name = aDecoder.decodeObject(forKey: "name") as! String
    age = aDecoder.decodeInteger(forKey: "age")
}

Forced unwrapping the string is 100% safe since the value is always encoded as non-optional.

Save the array

let savedData = NSKeyedArchiver.archivedData(withRootObject: array)
UserDefaults.standard.set(savedData, forKey: "myPeople")

Load the array

if let savedData = UserDefaults.standard.object(forKey: "myPeople") as? Data {
    array = NSKeyedUnarchiver.unarchiveObject(with: savedData) as! [Person]
}

Forced unwrapping is also safe in this case if the optional binding as? Data succeeds.

Lawliet · Accepted Answer · 2017-07-10 13:51:42Z

1

You should not force unwrapping. Try getting

required init (coder aDecoder: NSCoder) {
    name = (aDecoder.decodeObject(forKey: "name") as? String)!
    age = (aDecoder.decodeObject(forKey: "age") as? Int)!
}

replaced by

required init (coder aDecoder: NSCoder) {
    name = aDecoder.decodeObject(forKey: "name") as? String ?? ""
    age = aDecoder.decodeInteger(forKey: "age")
}

Get

let saveddata = UserDefaults.standard.object(forKey: "myPeople") as? Data
if saveddata != nil{
    array = (NSKeyedUnarchiver.unarchiveObject(with: saveddata!) as? [person])!
}

replaced by

if let data = UserDefaults.standard.object(forKey: "myPeople"),
    let array = NSKeyedUnarchiver.unarchiveObject(with: data as! Data) as? [person] {
    persons = array
}

I have tested. The code is working fine.

let person1 = person(name: "Bob", age: 22)
let person2 = person(name: "John", age: 10)
var persons = [person1, person2]

// Save data
let data = NSKeyedArchiver.archivedData(withRootObject: persons)
let defaults = UserDefaults.standard
defaults.set(data, forKey: "myPeople")

// Load data
if let data = UserDefaults.standard.object(forKey: "myPeople"),
    let array = NSKeyedUnarchiver.unarchiveObject(with: data as! Data) as? [person] {
    persons = array
}

Additionally, it is conventional to capitalise the first letter of a class name. You can check this out for naming convention.

edited Jul 10, 2017 at 13:51

answered Jul 10, 2017 at 13:14

Lawliet

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3 Comments

Charles B. Over a year ago

Thank you for answering however xcode doesn't allow me to not force unwrapping. It tells me to add as! Int after the age

Charles B. Over a year ago

My app now doesn't crash but puts the name and age of every person as "" and 0

vadian Over a year ago

Forced unwrapping is perfectly fine in this case. The class encodes always both non-optional properties so decoding the data can never be nil.

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