Swift 4可解码，直到解码时才知道密钥

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
        }
      ]
    }
  ]

在这里，我们有一系列词典；第一个具有键categoryName和Trending，第二个具有键categoryName和Comedy. categoryName键的值告诉我第二个键的名称.如何使用Decodable来表达这一点?

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

关键在于如何定义CodingKeys属性.尽管最常见的是enum，它可以是符合CodingKey协议的任何内容.要创建动态键，您可以调用静态函数:

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)

(由于我认为这是拼写错误，所以将JSON中的isFavourit更改为isFavourite.如果不是这样，很容易修改代码)

(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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