Swift 4: how to implement codable protocol for json array of different types

Question

Can somebody enlighten me how to implement codable protocol to swift structs, for the following json array of multiple types?

In the following json array of materials, it can be reflection object, video or note objects.

{
  "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"
      }
    }
  ]
}

Gereon · Accepted Answer · 2017-12-29 14:37:02Z

2

If you can live with a Material that has three optional properties, this is quite straightforward:

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

struct Material: Codable {
    let reflection: Reflection?
    let video: Video?
    let note: Note?
}

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 = JSONDecoder().decode(Response.self, from: data)

answered Dec 29, 2017 at 14:37

Gereon

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7 Comments

lionserdar Over a year ago

you should read this doc developer.apple.com/documentation/foundation/…

Mikhail Churbanov Over a year ago

The other "harder" way is using enum - but you will need to implement Codable protocol methods for it, e.g. something like in this example code (based on @Gereon answer)

Kyaw Htet Soe Over a year ago

thank so much @MikhailChurbanov (: your answer seems more precise but what's the difference though, why should use enum for this case instead of above answers?

Kyaw Htet Soe Over a year ago

@Gereon, what do you think about Mikhail answer?

Mikhail Churbanov Over a year ago

Absolutely agree with @Gereon - it's all about usage and personal taste. As for me if it's something not too big and stable (in some way) I would choose the if let - if over-complication doesn't bring you benefits, then it's more harmful than useful. The enums on the other hand are imho better in complex dynamic (evolving) projects - for example if you add a new type to support - exhaustive requirement for switch statements would be a great help in automatically finding all the places where you need to handle it.

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