How to save objects with sub-classes using NSKeyedArchiver in Swift IOS

Question

I'm just trying coding in Swift and I am trying to modify this existing project in the Apple Dev Library re: Meals.

I was hoping to put in an additional subclass such as Ingredients into the main Meal class having it as an array or ingredients.

import UIKit
import os.log

class Meal: NSObject, NSCoding {

    //MARK: Properties

    var name: String
    var photo: UIImage?
    var rating: Int
    var recipe: [ingredients]?

    //MARK: Archiving Paths
    static let DocumentsDirectory = FileManager().urls(for: .documentDirectory, in: .userDomainMask).first!
    static let ArchiveURL = DocumentsDirectory.appendingPathComponent("meals")

    //MARK: Types

    struct PropertyKey {
        static let name = "name"
        static let photo = "photo"
        static let rating = "rating"
        static let recipe = "recipe"
    }

    //MARK: Initialization

    init?(name: String, photo: UIImage?, rating: Int, recipe: ingredients!) {

        // The name must not be empty
        guard !name.isEmpty else {
            return nil
        }

        // The rating must be between 0 and 5 inclusively
        guard (rating >= 0) && (rating <= 5) else {
            return nil
        }

        // Initialization should fail if there is no name or if the rating is negative.
        if name.isEmpty || rating < 0  {
            return nil
        }

        // Initialize stored properties.
        self.name = name
        self.photo = photo
        self.rating = rating
        self.recipe = recipe
    }

    //MARK: NSCoding

    func encode(with aCoder: NSCoder) {
        aCoder.encode(name, forKey: PropertyKey.name)
        aCoder.encode(photo, forKey: PropertyKey.photo)
        aCoder.encode(rating, forKey: PropertyKey.rating)
        aCoder.encode(recipe, forKey: PropertyKey.recipe)
    }

    required convenience init?(coder aDecoder: NSCoder) {

        // The name is required. If we cannot decode a name string, the initializer should fail.
        guard let name = aDecoder.decodeObject(forKey: PropertyKey.name) as? String else {
            os_log("Unable to decode the name for a Meal object.", log: OSLog.default, type: .debug)
            return nil
        }

        // Because photo is an optional property of Meal, just use conditional cast.
        let photo = aDecoder.decodeObject(forKey: PropertyKey.photo) as? UIImage

        let rating = aDecoder.decodeInteger(forKey: PropertyKey.rating)

        let recipe = aDecoder.decodeObject(forKey: PropertyKey.recipe)

        // Must call designated initializer.
        self.init(name: name, photo: photo, rating: rating, recipe: recipe)

    }
}

Function calls for saving and loading the Meal items are as follows:

   private func saveMeals() {
        let isSuccessfulSave = NSKeyedArchiver.archiveRootObject(meals, toFile: Meal.ArchiveURL.path)
        if isSuccessfulSave {
            os_log("Meals successfully saved.", log: OSLog.default, type: .debug)
        } else {
            os_log("Failed to save meals...", log: OSLog.default, type: .error)
        }
    }

    private func loadMeals() -> [Meal]?  {
        return NSKeyedUnarchiver.unarchiveObject(withFile: Meal.ArchiveURL.path) as? [Meal]
    }

I declared a new Class Ingredients.swift to capture the ingredients that I wanted.

import UIKit
import os.log

class Ingredients: NSObject {

    struct PropertyKey {
        static let name = "name"
        static let  quantity = "quantity"
    }

    var name: String!
    var quantity: Double!

    //MARK: Initialization

    init?(name: Int, quantity: Double) {

        self.name = name
        self.quantity = quantity
    }
}

The problem I am having now is that the XCode is throwing a "Terminating app due to uncaught exception

'NSInvalidArgumentException', reason: '-[MealTracker.Ingredients encodeWithCoder:]: unrecognized selector sent to instance 0x1c40a0e40'"

Can I please know how to successfully include the Ingredients array into the saved object?

Answer 1

You have to implement NSCoding protocol

func encode(with aCoder: NSCoder) {}
required convenience init?(coder aDecoder: NSCoder) {}

Inside the inner custom classes also

class Ingredients: NSObject , NSCoding {}