Swift 4 Codable解碼json

Question

我正在嘗試實現新的Codable協議，所以我將Codable添加到我的結構中，但我仍然堅持解碼JSON 。

這是我以前的所作所為：

結構 -

struct Question {
    var title: String
    var answer: Int
    var question: Int
}

客戶 -

...

guard let data = data else {
    return
}

do {
    self.jsonResponse = try JSONSerialization.jsonObject(with: data, options: .allowFragments) as? [String: Any]
    let questionItems = self.jsonResponse?["themes"] as! [[String: Any]]

    questionItems.forEach {
        let item = Question(title: $0["title"] as! String,
                            answer: $0["answer"] as! Int,
                            question: $0["question"] as! Int)
        questionData.append(item)
    }

} catch {
    print("error")
}

這就是我現在所擁有的，除了我無法弄清楚解碼器部分：

結構 -

struct Question: Codable {
    var title: String
    var answer: Int
    var question: Int
}

客戶 -

...

let decoder = JSONDecoder()
if let questions = try? decoder.decode([Question].self, from: data) {
    // Can't get past this part
} else {
    print("Not working")
}

它打印“不工作”，因為我無法通過decoder.decode部分。 有任何想法嗎？ 將根據需要發布任何額外的代碼，謝謝！

編輯：

API JSON的示例：

{
  "themes": [
    {
      "answer": 1,
      "question": 44438222,
      "title": "How many letters are in the alphabet?"
    },
    {
      "answer": 0,
      "question": 44438489,
      "title": "This is a random question"
    }
  ]
 }

如果我打印self.jsonResponse我得到這個：

Optional(["themes": <__NSArrayI 0x6180002478f0>(
{
    "answer" = 7;
    "question" = 7674790;
    title = "This is the title of the question";
},
{
    "answer_" = 2;
    "question" = 23915741;
    title = "This is the title of the question";
}

我的新代碼：

struct Theme: Codable {
    var themes : [Question]
}

struct Question: Codable {
    var title: String
    var answer: Int
    var question: Int
}

...

if let decoded = try? JSONDecoder().decode(Theme.self, from: data) {
    print("decoded:", decoded)
} else {
    print("Not working")
}

Answer 1

如果你的JSON有一個結構

{"themes" : [{"title": "Foo", "answer": 1, "question": 2},
             {"title": "Bar", "answer": 3, "question": 4}]}

你需要一個等效的themes對象。 添加此結構

struct Theme : Codable {
    var themes : [Question]
}

現在您可以解碼JSON：

if let decoded = try? JSONDecoder().decode(Theme.self, from: data) {
    print("decoded:", decoded)
} else {
    print("Not working")
}

包含的Question對象被隱式解碼。

Answer 2

您收到此錯誤是因為您的JSON可能是這樣構造的：

{
  "themes": [
    { "title": ..., "question": ..., "answer": ... },
    { "title": ..., "question": ..., "answer": ... },
    { ... }
  ],
  ...
}

但是，您編寫的代碼需要頂級的[Question] 。 你需要的是一個不同的頂級類型，它具有一個[Question]的themes屬性。 當您解碼該頂級類型時，您的[Question]將被解碼為themes鍵。

Answer 3

您好@all我已經為Swift 4添加了JSON編碼和解碼的代碼。

請使用此處的鏈接