Swift 4 可解码多个容器

Question

我试图了解如何将这个多容器 JSON 解析为一个对象。我已经尝试过这种方法（Mark answer），但他解释了如何使用一级容器解决它。出于某种原因，我无法模仿多个容器的行为。

 {
     "graphql": {
        "shortcode_media": {
          "id": "1657677004214306744",
          "shortcode": "BcBQHPchwe4"
        }
     }
  }

---

class Post: Decodable {


    enum CodingKeys: String, CodingKey {
        case graphql // The top level "user" key
        case shortcode_media
    }

    enum PostKeys: String, CodingKey {
        case id
    }

    required init(from decoder: Decoder) throws {

        let values = try decoder.container(keyedBy: CodingKeys.self)

        let post = try values.nestedContainer(keyedBy: PostKeys.self, forKey: .shortcode_media)

        self.id = try post.decode(String.self, forKey: .id)

    }

    var id: String

}

我越来越：

Swift.DecodingError.Context(codingPath: [], debugDescription: "Cannot get KeyedDecodingContainer<PostKeys> -- no value found for key \"shortcode_media\"", underlyingError: nil))

任何帮助将不胜感激，谢谢！

Answer 1

正如 vadian 指出的那样，您没有匹配 JSON 结构。没有shortcode_media像您在CodingKeys.

为了使用自定义解码器对其进行解码，您需要遍历每个级别并进行处理。

class Post: Decodable {

    enum CodingKeys: String, CodingKey {
        case graphql
    }

    enum GraphQLKeys: String, CodingKey {
        case shortcode_media
    }

    enum PostKeys: String, CodingKey {
        case id
    }

    required init(from decoder: Decoder) throws {
        // unload the top level
        let container = try decoder.container(keyedBy: CodingKeys.self)
        // Unload the graphql key
        let graphql = try container.nestedContainer(keyedBy: GraphQLKeys.self, forKey: .graphql)
        // unload the shortcode_media key
        let post = try graphql.nestedContainer(keyedBy: PostKeys.self, forKey: .shortcode_media)

        // Finally, unload the actual object
        self.id = try post.decode(String.self, forKey: .id)
    }

    var id: String

}