Swift 4 可解码，直到解码时间才知道密钥 [英] Swift 4 Decodable with keys not known until decoding time

问题描述

Swift 4 Decodable 协议如何处理包含名称直到运行时才知道的键的字典?例如:

How does the Swift 4 Decodable protocol cope with a dictionary containing a key whose name is not known until runtime? For example:

  [
    {
      "categoryName": "Trending",
      "Trending": [
        {
          "category": "Trending",
          "trailerPrice": "",
          "isFavourit": null,
          "isWatchlist": null
        }
      ]
    },
    {
      "categoryName": "Comedy",
      "Comedy": [
        {
          "category": "Comedy",
          "trailerPrice": "",
          "isFavourit": null,
          "isWatchlist": null
        }
      ]
    }
  ]

这里我们有一个字典数组；第一个有键categoryName 和Trending，而第二个有键categoryName 和Comedy.categoryName 键的值告诉我第二个键的名称.我如何使用 Decodable 表达这一点?

Here we have an array of dictionaries; the first has keys categoryName and Trending, while the second has keys categoryName and Comedy. The value of the categoryName key tells me the name of the second key. How do I express that using Decodable?

推荐答案

关键在于您如何定义 CodingKeys 属性.虽然它最常见的是 enum，但它可以是任何符合 CodingKey 协议的东西.并且要制作动态键，您可以调用一个静态函数:

The key is in how you define the CodingKeys property. While it's most commonly an enum it can be anything that conforms to the CodingKey protocol. And to make dynamic keys, you can call a static function:

struct Category: Decodable {
    struct Detail: Decodable {
        var category: String
        var trailerPrice: String
        var isFavorite: Bool?
        var isWatchlist: Bool?
    }

    var name: String
    var detail: Detail

    private struct CodingKeys: CodingKey {
        var intValue: Int?
        var stringValue: String

        init?(intValue: Int) { self.intValue = intValue; self.stringValue = "(intValue)" }
        init?(stringValue: String) { self.stringValue = stringValue }

        static let name = CodingKeys.make(key: "categoryName")
        static func make(key: String) -> CodingKeys {
            return CodingKeys(stringValue: key)!
        }
    }

    init(from coder: Decoder) throws {
        let container = try coder.container(keyedBy: CodingKeys.self)
        self.name = try container.decode(String.self, forKey: .name)
        self.detail = try container.decode([Detail].self, forKey: .make(key: name)).first!
    }
}

用法:

let jsonData = """
  [
    {
      "categoryName": "Trending",
      "Trending": [
        {
          "category": "Trending",
          "trailerPrice": "",
          "isFavourite": null,
          "isWatchlist": null
        }
      ]
    },
    {
      "categoryName": "Comedy",
      "Comedy": [
        {
          "category": "Comedy",
          "trailerPrice": "",
          "isFavourite": null,
          "isWatchlist": null
        }
      ]
    }
  ]
""".data(using: .utf8)!

let categories = try! JSONDecoder().decode([Category].self, from: jsonData)

(我将 JSON 中的 isFavourit 更改为 isFavourite 因为我认为这是拼写错误.如果不是这种情况，调整代码很容易)

(I changed isFavourit in the JSON to isFavourite since I thought it was a mispelling. It's easy enough to adapt the code if that's not the case)

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