swift-4-how-to-implement-codable-protocol-for-json-array-of-different-types

gistfile1.txt

import Foundation

let dataString = "{  \"materials\": [    {      \"reflection\": {        \"title\": \"3-2-1 reflection\",        \"description\": \"please reflect after today\",        \"questions\": [          {            \"question\": \"question 1\",            \"answer\": \"answer 1\",            \"answerImageUrl\": \"http://xxx\"          },          {            \"question\": \"question 1\",            \"answer\": \"answer 1\",            \"answerImageUrl\": \"http://xxx\"          }        ]      }    },    {      \"video\": {        \"title\": \"the jungle\",        \"description\": \"please watch after today lesson\",        \"videoUrl\": \"http://\"      }    },    {      \"note\": {        \"title\": \"the note\",        \"description\": \"please read after today lesson\"      }    }  ]}"
let data = dataString.data(using: .utf8)!

struct Response: Codable {
    let materials: [Material]
}

enum Material: Codable {
    case video(Video)
    case reflection(Reflection)
    case note(Note)

    enum CodingKeys: String, CodingKey {
        case video
        case reflection
        case note
    }
    
    struct UnknownMaterialError: Error {}
    
    init(from decoder: Decoder) throws {
        let values = try decoder.container(keyedBy: CodingKeys.self)
        
        if let video = try? values.decode(Video.self, forKey: CodingKeys.video) {
            self = .video(video)
        } else if let reflection = try? values.decode(Reflection.self, forKey: CodingKeys.reflection) {
            self = .reflection(reflection)
        } else if let note = try? values.decode(Note.self, forKey: CodingKeys.note) {
            self = .note(note)
        } else {
            throw UnknownMaterialError()
        }
    }
    
    func encode(to encoder: Encoder) throws -> () {
        switch self {
	    case .video(let video):
	        try video.encode(to: encoder)
	    case .reflection(let reflection):
	        try reflection.encode(to: encoder)
        case .note(let note):
	        try note.encode(to: encoder)
	    }
    }
}

struct Video: Codable {
    let title, description, videoUrl: String
}

struct Reflection: Codable {
    let title, description: String
    let questions: [Question]
}

struct Question: Codable {
    let question, answer, answerImageUrl: String
}

struct Note: Codable {
    let title, description: String
}

let response = try JSONDecoder().decode(Response.self, from: data)
print (response)