在 Swift 4 上解码 JSON 数据返回 nil

Question

I'm trying to decode my json data with below function. I had different Json format at first and It was working but whenI change json format, It started not to work. I try to do changes also in Structure code but nothing worked. What Am I missing? (Code is for first Json format so It needs to be work on second format too)

First JSON:

{
"status": 200,
"results": [
    {
        "group_matched": false,
        "distance_mi": 4,
        "content_hash": "1rT2lirUapfrYIYxSR2u0GtmRSLPsVki9kFj4ugs8JIq6",
        "common_friends": [],
        "common_likes": [],
        "common_friend_count": 0,
        "common_like_count": 0,
        "connection_count": 0,
        "_id": "5a2805ba779f34267d32d8b0",
        "bio": "",
            "birth_date": "1997-12-09T16:28:29.761Z",
            "name": "John", 
        },

Second JSON:

{
    "meta": {
        "status": 200
    },
    "data": {
        "results": [
            {
                "type": "user",
                "user": {
                    "_id": "545001b33bf179416a30bf7f",
                    "bio": "Ä°nstagram:",
                    "birth_date": "1992-12-09T17:12:49.957Z",
                    "name": "",
                    "photos": [
                        {
                            "id": "2eb1beec-6180-4d58-90fd-5f076da96af9",
                            "url": "",
                            "processedFiles": [
                                {
                                    "url": "",
                                    "height": 640,
                                    "width": 640
                                },
                                {
                                    "url": "",
                                    "height": 320,
                                    "width": 320
                                },
                                {
                                    "url": "",
                                    "height": 172,
                                    "width": 172
                                },
                                {
                                    "url": "",
                                    "height": 84,
                                    "width": 84
                                }
                            ]
                        },
                        {
                            "id": "89d2bc07-d244-457b-b610-26ecd4e9e86d",
                            "url": "",
                            "processedFiles": [
                                {
                                    "url": "",
                                    "height": 640,
                                    "width": 640
                                },
                                {
                                    "url": "",
                                    "height": 320,
                                    "width": 320
                                },
                                {
                                    "url": "",
                                    "height": 172,
                                    "width": 172
                                },
                                {
                                    "url": "",
                                    "height": 84,
                                    "width": 84
                                }
                            ]
                        },
                        {
                            "id": "0fcafc7e-d6e7-4cc5-891a-735971d6a5b2",
                            "url": "",
                            "processedFiles": [
                                {
                                    "url": "",
                                    "height": 640,
                                    "width": 640
                                },
                                {
                                    "url": "g",
                                    "height": 320,
                                    "width": 320
                                },
                                {
                                    "url": "",
                                    "height": 172,
                                    "width": 172
                                },
                                {
                                    "url": "",
                                    "height": 84,
                                    "width": 84
                                }
                            ]
                        },
                        {
                            "id": "bac74531-09e7-4c5b-ac6c-cab36c4be587",
                            "url": "",
                            "processedFiles": [
                                {
                                    "url": "",
                                    "height": 640,
                                    "width": 640
                                },
                                {
                                    "url": "",
                                    "height": 320,
                                    "width": 320
                                },
                                {
                                    "url": "",
                                    "height": 172,
                                    "width": 172
                                },
                                {
                                    "url": "",
                                    "height": 84,
                                    "width": 84
                                }
                            ]
                        },
                        {
                            "id": "3c216244-946a-4c58-8670-cc12c05801cb",
                            "url": "",
                            "processedFiles": [
                                {
                                    "url": "",
                                    "height": 640,
                                    "width": 640
                                },
                                {
                                    "url": "",
                                    "height": 320,
                                    "width": 320
                                },
                                {
                                    "url": "",
                                    "height": 172,
                                    "width": 172
                                },
                                {
                                    "url": "",
                                    "height": 84,
                                    "width": 84
                                }
                            ]
                        },
                        {
                            "id": "-8672-488d-8b7e-f30b4560c56b",
                            "url": "",
                            "processedFiles": [
                                {
                                    "url": "",
                                    "height": 640,
                                    "width": 640
                                },
                                {
                                    "url": "",
                                    "height": 320,
                                    "width": 320
                                },
                                {
                                    "url": "",
                                    "height": 172,
                                    "width": 172
                                },
                                {
                                    "url": "",
                                    "height": 84,
                                    "width": 84
                                }
                            ]
                        }
                    ],
                    "gender": 1,

Struct Code:

    struct Photo: Codable{
    var url: String?
    var processedFiles: [processedFiles]?
}
struct User: Codable{
    var group_matched: Bool?
    var distance_mi: Int?
    var common_friend_count: Int?
    var name:String?
    var profile_picture: String?
    var instagram_id: String?
    var photos: [Photo]?
}
class Results : Codable {
    var results: [User] = []
    static let sharedResults = Results()
    private init() { }
    var type: String?

    func populateData(sender: Results){
        print(sender)
        results += sender.results
    }
}

Decode Code:

 let jsonData = JSON(data: response.data!)
                let jsonData2 = try? JSONSerialization.data(withJSONObject: jsonData["data"].object)
                print(JSON(data: jsonData2!))

                let decoder = JSONDecoder()
                var response_class = Results.sharedResults
                response_class = try decoder.decode(Results.self, from: jsonData2!)
                Results.sharedResults.populateData(sender: response_class)

EDIT: I edit second JSON, It now has array of array. How Can I implement decoder keys for that second array?

Answer 1

In this case I would write a custom initializer with nestedContainer to include the user dictionary into the parent object

let jsonString = """
{
    "meta": {
        "status": 200
    },
    "data": {
        "results": [
        {
            "type": "user",
            "user": {
                "_id": "545001b33bf179416a30bf7f",
                "bio": "Ä°nstagram:hello",
                "birth_date": "1992-12-09T17:12:49.957Z",
                "name": "Hello"
            },

            "group_matched": false,
            "distance_mi": 4
        }
      ]
    }
}
"""

---

struct Root : Decodable {
    let meta : [String:Int]
    let data : Result
}

struct Result : Decodable {
    let results : [User]
}

struct User : Decodable {

    let type : String
    let groupMatched : Bool
    let distanceMi : Int

    let id, bio, birthDate, name : String

    private enum CodingKeys : String, CodingKey {
        case type, user, groupMatched = "group_matched", distanceMi = "distance_mi"
    }

    private enum UserKeys: String, CodingKey {
        case id = "_id", bio, birthDate = "birth_date", name
    }

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        type = try container.decode(String.self, forKey: .type)
        groupMatched = try container.decode(Bool.self, forKey: .groupMatched)
        distanceMi = try container.decode(Int.self, forKey: .distanceMi)

        let userInfo = try container.nestedContainer(keyedBy: UserKeys.self, forKey: .user)
        id = try userInfo.decode(String.self, forKey: .id)
        bio = try userInfo.decode(String.self, forKey: .bio)
        birthDate = try userInfo.decode(String.self, forKey: .birthDate)
        name = try userInfo.decode(String.self, forKey: .name)
    }
}

---

do {
     let data = Data(jsonString.utf8)
     let decoder = JSONDecoder() 
     let root = try decoder.decode(Root.self, from: data)
     print(root)       
} catch {
     print("error: ", error)
}

Answer 2

By making the result of JSONDecoder().decode an optional ( try? ), you are ensuring that you get nil if the decoding goes wrong. You can catch decoding related issues quickly by implementing proper catch blocks. Eg:

do {
    let decoder = JSONDecoder()
    let messages = try decoder.decode(Results.self, from: data)
    print(messages as Any)
} catch DecodingError.dataCorrupted(let context) {
    print(context)
} catch DecodingError.keyNotFound(let key, let context) {
    print("Key '\(key)' not found:", context.debugDescription)
    print("codingPath:", context.codingPath)
} catch DecodingError.valueNotFound(let value, let context) {
    print("Value '\(value)' not found:", context.debugDescription)
    print("codingPath:", context.codingPath)
} catch DecodingError.typeMismatch(let type, let context) {
    print("Type '\(type)' mismatch:", context.debugDescription)
    print("codingPath:", context.codingPath)
} catch {
    print("error: ", error)
}

Not a direct answer to your question, but surely will reduce other's time to understand which part of decoding is going wrong.