Parsing JSON with Swift 4 Decodable - json

Question

I have been getting the following error every time I try to parse JSON in my program. I can't seem to figure it out.
"Expected to decode String but found an array instead.", underlyingError: nil
Here is the code I have been struggling with:
struct Book: Decodable {
let id: Int
let title: String
let chapters: Int
var pages: [Page]?
}
struct Page: Decodable {
let id: Int
let text: [String]
}
struct Chapter: Decodable {
var chapterNumber: Int
}
func fetchJSON() {
let urlString = "https://api.myjson.com/bins/kzqh3"
guard let url = URL(string: urlString) else { return }
URLSession.shared.dataTask(with: url) { (data, _, err) in
if let err = err {
print("Failed to fetch data from", err)
return
}
guard let data = data else { return }
do {
let decoder = JSONDecoder()
let books = try decoder.decode([Book].self, from: data)
books.forEach({print($0.title)})
} catch let jsonErr {
print("Failed to parse json:", jsonErr)
}
}.resume()
}

Answer 1

Are you sure that's the real error message?
Actually the error is supposed to be
"Expected to decode String but found a dictionary instead."
The value for key text is not an array of strings, it's an array of dictionaries
struct Page: Decodable {
let id: Int
let text: [[String:String]]
}
The struct Chapter is not needed.
Alternatively write a custom initializer and decode the dictionaries containing the chapter number as key and the text as value into an array of Chapter
struct Book: Decodable {
let id: Int
let title: String
let chapters: Int
let pages: [Page]
}
struct Page: Decodable {
let id: Int
var chapters = [Chapter]()
private enum CodingKeys : String, CodingKey { case id, chapters = "text" }
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
id = try container.decode(Int.self, forKey: .id)
var arrayContainer = try container.nestedUnkeyedContainer(forKey: .chapters)
while !arrayContainer.isAtEnd {
let chapterDict = try arrayContainer.decode([String:String].self)
for (key, value) in chapterDict {
chapters.append(Chapter(number: Int(key)!, text: value))
}
}
}
}
struct Chapter: Decodable {
let number : Int
let text : String
}

Answer 2

This is working:
import UIKit
class ViewController: UIViewController {
private var books = [Book]()
struct Book: Decodable {
let id: Int
let title: String
let chapters: Int
var pages: [Page]
}
struct Page: Decodable {
let id: Int
let text: [[String:String]]
}
override func viewDidLoad() {
super.viewDidLoad()
fetchJSON()
}
func fetchJSON() {
let urlString = "https://api.myjson.com/bins/kzqh3"
guard let url = URL(string: urlString) else { return }
URLSession.shared.dataTask(with: url) { data, response, error in
if error != nil {
print(error!.localizedDescription)
return
}
guard let data = data else { return }
do {
let decoder = JSONDecoder()
self.books = try decoder.decode([Book].self, from: data)
DispatchQueue.main.async {
for info in self.books {
print(info.title)
print(info.chapters)
print(info.pages[0].id)
print(info.pages[0].text)
print("-------------------")
}
}
} catch let jsonErr {
print("something wrong after downloaded: \(jsonErr) ")
}
}.resume()
}
}
// print
//Genesis
//50
//1
//[["1": "In the beg...]]
//-------------------
//Exodus
//40
//2
//[["1": "In the beginning God created...]]
//
If you need to print the value of each chapter in the book, I can use something like this:
import UIKit
class ViewController: UIViewController {
private var books = [Book]()
struct Book: Decodable {
let id: Int
let title: String
let chapters: Int
var pages: [Page]
}
struct Page: Decodable {
let id: Int
let text: [[String:String]]
}
override func viewDidLoad() {
super.viewDidLoad()
fetchJSON()
}
func fetchJSON() {
let urlString = "https://api.myjson.com/bins/kzqh3"
guard let url = URL(string: urlString) else { return }
URLSession.shared.dataTask(with: url) { data, response, error in
if error != nil {
print(error!.localizedDescription)
return
}
guard let data = data else { return }
do {
let decoder = JSONDecoder()
self.books = try decoder.decode([Book].self, from: data)
DispatchQueue.main.async {
for info in self.books {
print(info.title)
print(info.chapters)
print(info.pages[0].id)
//print(info.pages[0].text)
for cc in info.pages[0].text {
for (key, value) in cc {
print("\(key) : \(value)")
}
}
print("-------------------")
}
}
} catch let jsonErr {
print("something wrong after downloaded: \(jsonErr) ")
}
}.resume()
}
}
//Genesis
//50
//1
//1 : In the beginning God ...
//2 : But the earth became waste...
//.
//.
//.
//31 : And God saw everything...
//-------------------
//Exodus
//40
//2
//1 : In the beginning God...
//2 : But the earth became...
//.
//.
//.
//31 : And God saw everything