Swift 4.1 Decodable 无法使用 nestedContainer 解码嵌套数组

Question

尝试使用 Codable 编写一个简单的 Swift 4.1 来解析 json。

我有一个 struct 这样的：

struct GameCharacter : Codable {
  var name : String
  var weapons : [Weapon]
  enum CodingKeys : String, CodingKey {
    case name
    case weapons
  }

  init(from decoder: Decoder) {
    do {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.name = try container.decode(String.self, forKey: .name)
        let weaponsContainer = try container.nestedContainer(keyedBy: Weapon.CodingKeys.self, forKey: .weapons)
        self.weapons = try weaponsContainer.decode([Weapon].self, forKey: .weapons)

    } catch let error {
        print("error: \(error)")
        fatalError("error is \(error)")
    }
  }
}

还有一个像这样：

struct Weapon : Codable {    
  var name : String
  enum CodingKeys : String, CodingKey {
    case name
  }

  init(from decoder: Decoder) {
    do {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.name = try container.decode(String.self, forKey: .name)
    } catch let error {
        print("error: \(error)")
        fatalError("error is \(error)")
    }
  }
}

我也有一个 struct 这样的包装器：

struct Game : Codable {
  var characters : [GameCharacter]
  enum CodingKeys : String, CodingKey { case characters }
}

json 数据如下所示：

{ 
  "characters" : [{
    "name" : "Steve",
    "weapons" : [{
      "name" : "toothpick"
    }]
  }]
}

但是，我总是收到类型不匹配错误：

error: typeMismatch(Swift.Dictionary, Swift.DecodingError.Context(codingPath: [CodingKeys(stringValue: "characters", intValue: nil), _JSONKey(stringValue: "Index 0", intValue: 0)], debugDescription: "Expected to decode Dictionary but found an array instead.", underlyingError: nil))

这一行：

let weaponsContainer = try container.nestedContainer(keyedBy: Weapon.CodingKeys.self, forKey: .weapons)

我不确定问题出在哪里，因为我显然（在我看来）要求一系列武器，但它认为我正在寻找字典。

想知道是否有人知道我遗漏了什么。

Answer 1

nestedContainers 只有当你想将子字典或子数组解码到父结构中时才需要——例如将 weapons 对象解码到 Game 结构中——事实并非如此，因为您声明了所有嵌套结构。

要解码 JSON 你可以省略所有 CodingKeys 和初始化器，利用 Codable 的魔力，这就足够了：

struct Game : Codable {
    let characters : [GameCharacter]
}

struct GameCharacter : Codable {
    let name : String
    let weapons : [Weapon]
}

struct Weapon : Codable {
    let name : String
}

并称之为

do {
    let result = try JSONDecoder().decode(Game.self, from: data)
    print(result)
} catch { print(error) }

Answer 2

用以下不需要任何自定义初始化程序替换您的结构

import Foundation

struct Weapon: Codable {
    let characters: [Character]
}

struct Character: Codable {
    let name: String
    let weapons: [WeaponElement]
}

struct WeaponElement: Codable {
    let name: String
}

并创建

extension Weapon {
init(data: Data) throws {
    self = try JSONDecoder().decode(Weapon.self, from: data)
}

现在

 let weapon = try Weapon(json)

Answer 3

试试这个

let string = """
{
"characters" : [{
    "name" : "Steve",
    "weapons" : [{
    "name" : "toothpick"
        }]
    }]
}
"""

struct GameCharacter: Codable {
    let characters: [Character]
}

struct Character: Codable {
    let name: String
    let weapons: [Weapon]
}

struct Weapon: Codable {
    let name: String
}

let jsonData = string.data(using: .utf8)!
let decodr = JSONDecoder()

let result = try! decodr.decode(GameCharacter.self, from: jsonData)

let weapon = result.characters.flatMap {[=10=].weapons}

for weaponname in weapon {
    print(weaponname.name) //Output toothpick
}

Answer 4

我有同样的问题，JSONDecoder() 只解码了我的 JSON 的第一级，然后我通过从扩展的 class 正文中评论这些方法解决了这个问题来自 Codable

public class Response<T:Codable> : Codable {

    public let data : T?

//commented this two function and my problem Solved <3
//    enum CodingKeys: String, CodingKey {
//        case data
//    }
//    required public init(from decoder: Decoder) throws {
//        data = try T(from: decoder)
//    }


}

Swift 4.1 Decodable 无法使用 nestedContainer 解码嵌套数组

Swift 4.1 Decodable Can't decode nested array with nestedContainer

ios

swift

codable