swift - 使用 SWIFT 4 decoable 时出现未知上下文错误

Question

我正在尝试使用 Decodable，但我收到一条错误消息:

KeyedDecodingContainer < CodingKeys>(_box: Swift._KeyedDecodingContainerBox< Foundation.(unknown context at 0x102f06958)._JSONKeyedDecodingContainer< MealsParser.Entry.CodingKeys>>)

我不知道为什么。

这里是 JSON:

{
  "meals": {
    "breakfast": {
      "cost": 24,
      "min_price": 4
    },
    "lunch": {
      "cost": 12,
      "min_price": 2,
      "max_price": 20
    },
    "dinner": {
      "cost": 42
    }
  }
}

代码如下:

import UIKit


struct Meal: Decodable {
    var price: Int?
}

struct Entry: Decodable {

    enum CodingKeys: String, CodingKey {
        case meals
    }
    var meals: String?
    //    var meals: [String: Meal]

    public init(from decoder: Decoder) throws {
        var values = try decoder.container(keyedBy: CodingKeys.self)
        print(values)
    }
}




class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let url = Bundle.main.url(forResource: "meal", withExtension: "json")
        let data = try! Data(contentsOf: url!)

        let decoder = JSONDecoder()
        print(try! decoder.decode(Entry.self, from: data))
    }
}

如您所见，我什至无法解析包含关键餐点的容器。 稍后我希望能够解析膳食并创建内部结构等。但是，是的，我什至无法理解解析。

Answer 1

正确解码

struct Root: Codable {
    let meals: Meals
}

struct Meals: Codable {
    let breakfast: Breakfast
    let lunch: Lunch
    let dinner: Dinner
}

struct Breakfast: Codable {
    let cost, minPrice: Int

    enum CodingKeys: String, CodingKey {
        case cost
        case minPrice = "min_price"
    }
}

struct Dinner: Codable {
    let cost: Int
}

struct Lunch: Codable {
    let cost, minPrice, maxPrice: Int

    enum CodingKeys: String, CodingKey {
        case cost
        case minPrice = "min_price"
        case maxPrice = "max_price"
    }
}

//

do {

    let content = try JSONDecoder().decode(Root.self, from: data)

    print(content)
}
catch {

    print(error)
}