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从数组初始化的可解码

decodable swift json

0

Benjohn · 技术社区 · 5 年前

我有一个JSON对象数组。简而言之,它有以下形式:

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

Tubby 可以从数组中解码单个实例:

struct Tubby: Codable {
  let name: String
}

我想创建一个结构 Tubbies 可以从JSON数组中解码:

struct Tubbies: Codable {
   let tubbies: [Tubby]

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

但现在我被困在如何解码?我只想做:

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

但是 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

两者 ~~singleValueContainer~~ (这是一个错误,因为答案澄清了谢谢!)和 unkeyedContainer 向数组抛出一条消息,提示它们不支持数组。我能用一下吗 container(keyedBy:) ,我应该把什么作为钥匙?

1 回复 | 直到 5 年前

1

2

Mojtaba Hosseini 5 年前

我不认为这是个好办法,因为 [Tubby].self 但是,如果只想将数组包装到另一种类型中,则应该具有如下内容:

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)