时间戳

首页 > 解决方案 > 从数组初始化的可解码

json - 从数组初始化的可解码

问题描述

我有一个 JSON 对象数组。简而言之，它具有以下形式：

[
  {"name": "Tinky Winky"},
  {"name": "Dipsy"},
  {"name": "Laa-Laa"},
  {"name": "Po"}
]

我可以创建一个结构Tubby可以解码数组中的单个实例：

struct Tubby: Codable {
  let name: String
}

我想创建一个Tubbies可以从 JSON 数组解码的结构：

struct Tubbies: Codable {
   let tubbies: [Tubby]

   init(from decoder: Decoder) throws {
     // What goes here?
     tubbies = ???
   }

......但现在我不知道应该如何解码？我只想做：

   init(from decoder: Decoder) throws {
     // What goes here?
     tubbies = decoder.decode([Tubby].self)
   }

但Decoder不提供decode. 它有：

    /// Returns the data stored in this decoder as represented in a container
    /// keyed by the given key type.
    ///
    /// - parameter type: The key type to use for the container.
    /// - returns: A keyed decoding container view into this decoder.
    /// - throws: `DecodingError.typeMismatch` if the encountered stored value is
    ///   not a keyed container.
    func container<Key>(keyedBy type: Key.Type) throws -> KeyedDecodingContainer<Key> where Key : CodingKey

    /// Returns the data stored in this decoder as represented in a container
    /// appropriate for holding values with no keys.
    ///
    /// - returns: An unkeyed container view into this decoder.
    /// - throws: `DecodingError.typeMismatch` if the encountered stored value is
    ///   not an unkeyed container.
    func unkeyedContainer() throws -> UnkeyedDecodingContainer

    /// Returns the data stored in this decoder as represented in a container
    /// appropriate for holding a single primitive value.
    ///
    /// - returns: A single value container view into this decoder.
    /// - throws: `DecodingError.typeMismatch` if the encountered stored value is
    ///   not a single value container.
    func singleValueContainer() throws -> SingleValueDecodingContainer

两个都singleValueContainer（这是一个错误，因为答案澄清了 - 谢谢！）并unkeyedContainer抛出数组并显示一条消息，表明它们不支持数组。我可以使用container(keyedBy:)，我应该传递什么作为密钥？

标签： jsonswiftdecodable

解决方案

我认为这不是一个好方法，因为[Tubby].self它足够简单，可以在任何地方使用。但如果你只想将数组包装在另一种类型中，你应该有这样的东西：

详细版本：

struct Tubbies: Codable {
    let tubbies: [Tubby]
    
    init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()
        self.tubbies = try container.decode([Tubby].self)
    }
}

较短的版本：

struct Tubbies: Codable {
    let tubbies: [Tubby]
    
    init(from decoder: Decoder) throws {
        tubbies = try [Tubby](from: decoder)
    }
}

用法：

let tubbies: Tubbies = try! JSONDecoder().decode(Tubbies.self, from: jsonData)

推荐阅读