Property 'self.readCount' not initialized at super.init call - ios

Question

I have the following class
// LearningItem
class LearningItem : NSObject {
var id: String
var title: String
var subtitle: String?
var image: String
var uploadDate: Int
init(id: String, title: String, image: String, uploadDate: Int) {
self.id = id
self.title = title
self.image = image
self.uploadDate = uploadDate
}
I have another class
// Book.swift
class Book: LearningItem {
var publishDate: String?
var author: String?
var mediaUrl: String?
var video : String?
var tags: [String]?
var lists: [String: AnyObject]?
var readCount: Int
var categories: [String]?
var courses: [String]?
var amazonBuyUrl: String?
var starCount: Int
var read: Bool?
var completed = [String : Int]()
var stars = [String : Int]()
var completedDate : Int?
var desc: String
var epub: String
var authorDesc: String
init(id: String, title: String, desc: String, authorDesc: String, image: String, epub: String, readCount: Int, uploadDate: Int, starCount: Int) {
super.init(id: id, title: title, image: image, uploadDate: uploadDate)
self.id = id
self.desc = desc
self.authorDesc = authorDesc
self.title = title
self.epub = epub
self.image = image
self.readCount = readCount
self.uploadDate = uploadDate
self.starCount = starCount
}
I get the error "Property 'self.readCount' not initialized at super.init call"
where I call "super.init(id: id, title: title, image: image, uploadDate: uploadDate)" in Book.swift

Answer 1

Class initialisation not finished until it's designated initializers
not finished with initializing all properties
and after that you can call super class's designated initializers
Designated initializers are the primary initializers for a class. A designated initializer fully initializes all properties introduced by that class and calls an appropriate superclass initializer to continue the initialization process up the superclass chain.
SO
Class initialization in Swift is a two-phase process. In the first phase, each stored property is assigned an initial value by the class that introduced it. Once the initial state for every stored property has been determined, the second phase begins, and each class is given the opportunity to customize its stored properties further before the new instance is considered ready for use.
apple docs https://docs.swift.org/swift-book/LanguageGuide/Initialization.html
so
class Book: LearningItem {
var publishDate: String?
var author: String?
var mediaUrl: String?
var video : String?
var tags: [String]?
var lists: [String: AnyObject]?
var readCount: Int
var categories: [String]?
var courses: [String]?
var amazonBuyUrl: String?
var starCount: Int
var read: Bool?
var completed = [String : Int]()
var stars = [String : Int]()
var completedDate : Int?
var desc: String
var epub: String
var authorDesc: String
init(id: String, title: String, desc: String, authorDesc: String, image: String, epub: String, readCount: Int, uploadDate: Int, starCount: Int) {
self.readCount = readCount
self.starCount = starCount
self.desc = desc
self.epub = epub
self.authorDesc = authorDesc
super.init(id: id, title: title, image: image, uploadDate: uploadDate)
}
}