Swift 4.1 Decodable Can't decode nested array with nestedContainer - ios

Question

Trying to write a simple Swift 4.1 using Codable to parse json.
I have a struct like this:
struct GameCharacter : Codable {
var name : String
var weapons : [Weapon]
enum CodingKeys : String, CodingKey {
case name
case weapons
}
init(from decoder: Decoder) {
do {
let container = try decoder.container(keyedBy: CodingKeys.self)
self.name = try container.decode(String.self, forKey: .name)
let weaponsContainer = try container.nestedContainer(keyedBy: Weapon.CodingKeys.self, forKey: .weapons)
self.weapons = try weaponsContainer.decode([Weapon].self, forKey: .weapons)
} catch let error {
print("error: \(error)")
fatalError("error is \(error)")
}
}
}
and another like this:
struct Weapon : Codable {
var name : String
enum CodingKeys : String, CodingKey {
case name
}
init(from decoder: Decoder) {
do {
let container = try decoder.container(keyedBy: CodingKeys.self)
self.name = try container.decode(String.self, forKey: .name)
} catch let error {
print("error: \(error)")
fatalError("error is \(error)")
}
}
}
I also have a struct for the wrapper like this:
struct Game : Codable {
var characters : [GameCharacter]
enum CodingKeys : String, CodingKey { case characters }
}
The json data looks like this:
{
"characters" : [{
"name" : "Steve",
"weapons" : [{
"name" : "toothpick"
}]
}]
}
However, I am always getting a typeMismatcherror error:
error: typeMismatch(Swift.Dictionary,
Swift.DecodingError.Context(codingPath: [CodingKeys(stringValue:
"characters", intValue: nil), _JSONKey(stringValue: "Index 0",
intValue: 0)], debugDescription: "Expected to decode
Dictionary but found an array instead.", underlyingError:
nil))
on this line:
let weaponsContainer = try container.nestedContainer(keyedBy: Weapon.CodingKeys.self, forKey: .weapons)
I am not sure what the issue is, as I am clearly (in my view) asking for an array of Weapons, but it thinks I am looking for a dictionary anyway.
Wondering if anyone has any insight as to what I am missing.

Answer 1

nestedContainers is only needed if you want to decode a sub-dictionary or sub-array into the parent struct – for example decode the weapons object into the Game struct – which is not the case because you declared all nested structs.
To decode the JSON you can omit all CodingKeys and the initializers, take advantage of the magic of Codable, this is sufficient:
struct Game : Codable {
let characters : [GameCharacter]
}
struct GameCharacter : Codable {
let name : String
let weapons : [Weapon]
}
struct Weapon : Codable {
let name : String
}
and call it
do {
let result = try JSONDecoder().decode(Game.self, from: data)
print(result)
} catch { print(error) }

Answer 2

Replace your struct with following no need for any custom initializers
import Foundation
struct Weapon: Codable {
let characters: [Character]
}
struct Character: Codable {
let name: String
let weapons: [WeaponElement]
}
struct WeaponElement: Codable {
let name: String
}
And create
extension Weapon {
init(data: Data) throws {
self = try JSONDecoder().decode(Weapon.self, from: data)
}
Now just
let weapon = try Weapon(json)

Answer 3

try this
let string = """
{
"characters" : [{
"name" : "Steve",
"weapons" : [{
"name" : "toothpick"
}]
}]
}
"""
struct GameCharacter: Codable {
let characters: [Character]
}
struct Character: Codable {
let name: String
let weapons: [Weapon]
}
struct Weapon: Codable {
let name: String
}
let jsonData = string.data(using: .utf8)!
let decodr = JSONDecoder()
let result = try! decodr.decode(GameCharacter.self, from: jsonData)
let weapon = result.characters.flatMap {$0.weapons}
for weaponname in weapon {
print(weaponname.name) //Output toothpick
}

Answer 4

I Have the same problem, JSONDecoder() only decode the first level of my JSON and then I solve this problem with commented these methods from the body of my class that extended from Codable
public class Response<T:Codable> : Codable {
public let data : T?
//commented this two function and my problem Solved <3
// enum CodingKeys: String, CodingKey {
// case data
// }
// required public init(from decoder: Decoder) throws {
// data = try T(from: decoder)
// }
}