enum PostType: Decodable {
init(from decoder: Decoder) throws {
// What do i put here?
}
case Image
enum CodingKeys: String, CodingKey {
case image
}
}
我要怎么做才能完成这个?
此外，让我们说我把情况改为这样:
case image(value: Int)
我如何使这符合解码?
这是我的完整代码(不工作)
let jsonData = """
{
"count": 4
}
""".data(using: .utf8)!
do {
let decoder = JSONDecoder()
let response = try decoder.decode(PostType.self, from: jsonData)
print(response)
} catch {
print(error)
}
}
}
enum PostType: Int, Codable {
case count = 4
}
此外，它将如何处理这样的枚举?
enum PostType: Decodable {
case count(number: Int)
}
这很简单，只需使用String或Int原始值，这些值是隐式分配的。
enum PostType: Int, Codable {
case image, blob
}
图像编码为0,blob编码为1
Or
enum PostType: String, Codable {
case image, blob
}
图像被编码为Image而blob被编码为blob
这是一个简单的例子如何使用它:
enum PostType : Int, Codable {
case count = 4
}
struct Post : Codable {
var type : PostType
}
let jsonString = "{\"type\": 4}"
let jsonData = Data(jsonString.utf8)
do {
let decoded = try JSONDecoder().decode(Post.self, from: jsonData)
print("decoded:", decoded.type)
} catch {
print(error)
}
更新
在iOS 13.3+和macOS 15.1+中，允许对片段(未包装在集合类型中的单个JSON值)进行解码
let jsonString = "4"
let jsonData = Data(jsonString.utf8)
do {
let decoded = try JSONDecoder().decode(PostType.self, from: jsonData)
print("decoded:", decoded) // -> decoded: count
} catch {
print(error)
}
在Swift 5.5+中，甚至可以在不需要任何额外代码的情况下对枚举进行关联值的en /decode。这些值被映射到一个字典，并且必须为每个关联值指定一个参数标签
enum Rotation: Codable {
case zAxis(angle: Double, speed: Int)
}
let jsonString = #"{"zAxis":{"angle":90,"speed":5}}"#
let jsonData = Data(jsonString.utf8)
do {
let decoded = try JSONDecoder().decode(Rotation.self, from: jsonData)
print("decoded:", decoded)
} catch {
print(error)
}
这很简单，只需使用String或Int原始值，这些值是隐式分配的。
enum PostType: Int, Codable {
case image, blob
}
图像编码为0,blob编码为1
Or
enum PostType: String, Codable {
case image, blob
}
图像被编码为Image而blob被编码为blob
这是一个简单的例子如何使用它:
enum PostType : Int, Codable {
case count = 4
}
struct Post : Codable {
var type : PostType
}
let jsonString = "{\"type\": 4}"
let jsonData = Data(jsonString.utf8)
do {
let decoded = try JSONDecoder().decode(Post.self, from: jsonData)
print("decoded:", decoded.type)
} catch {
print(error)
}
更新
在iOS 13.3+和macOS 15.1+中，允许对片段(未包装在集合类型中的单个JSON值)进行解码
let jsonString = "4"
let jsonData = Data(jsonString.utf8)
do {
let decoded = try JSONDecoder().decode(PostType.self, from: jsonData)
print("decoded:", decoded) // -> decoded: count
} catch {
print(error)
}
在Swift 5.5+中，甚至可以在不需要任何额外代码的情况下对枚举进行关联值的en /decode。这些值被映射到一个字典，并且必须为每个关联值指定一个参数标签
enum Rotation: Codable {
case zAxis(angle: Double, speed: Int)
}
let jsonString = #"{"zAxis":{"angle":90,"speed":5}}"#
let jsonData = Data(jsonString.utf8)
do {
let decoded = try JSONDecoder().decode(Rotation.self, from: jsonData)
print("decoded:", decoded)
} catch {
print(error)
}
特性
简单的使用。可解码实例中的一行:line eg let enum: DecodableEnum<AnyEnum>
使用标准映射机制解码:JSONDecoder().decode(Model.self, from: data)
接收未知数据的覆盖情况(例如，如果您接收到意外数据，映射可解码对象将不会失败)
处理/传递映射或解码错误
细节
Xcode 12.0.1 (12A7300)
斯威夫特5.3
解决方案
import Foundation
enum DecodableEnum<Enum: RawRepresentable> where Enum.RawValue == String {
case value(Enum)
case error(DecodingError)
var value: Enum? {
switch self {
case .value(let value): return value
case .error: return nil
}
}
var error: DecodingError? {
switch self {
case .value: return nil
case .error(let error): return error
}
}
enum DecodingError: Error {
case notDefined(rawValue: String)
case decoding(error: Error)
}
}
extension DecodableEnum: Decodable {
init(from decoder: Decoder) throws {
do {
let rawValue = try decoder.singleValueContainer().decode(String.self)
guard let layout = Enum(rawValue: rawValue) else {
self = .error(.notDefined(rawValue: rawValue))
return
}
self = .value(layout)
} catch let err {
self = .error(.decoding(error: err))
}
}
}
使用示例
enum SimpleEnum: String, Codable {
case a, b, c, d
}
struct Model: Decodable {
let num: Int
let str: String
let enum1: DecodableEnum<SimpleEnum>
let enum2: DecodableEnum<SimpleEnum>
let enum3: DecodableEnum<SimpleEnum>
let enum4: DecodableEnum<SimpleEnum>?
}
let dictionary: [String : Any] = ["num": 1, "str": "blablabla", "enum1": "b", "enum2": "_", "enum3": 1]
let data = try! JSONSerialization.data(withJSONObject: dictionary)
let object = try JSONDecoder().decode(Model.self, from: data)
print("1. \(object.enum1.value)")
print("2. \(object.enum2.error)")
print("3. \(object.enum3.error)")
print("4. \(object.enum4)")
为了扩展@Toka的回答，你也可以在enum中添加一个原始的可表示值，并使用默认的可选构造函数来构建没有开关的enum:
enum MediaType: String, Decodable {
case audio = "AUDIO"
case multipleChoice = "MULTIPLE_CHOICES"
case other
init(from decoder: Decoder) throws {
let label = try decoder.singleValueContainer().decode(String.self)
self = MediaType(rawValue: label) ?? .other
}
}
它可以使用一个允许重构构造函数的自定义协议进行扩展:
protocol EnumDecodable: RawRepresentable, Decodable {
static var defaultDecoderValue: Self { get }
}
extension EnumDecodable where RawValue: Decodable {
init(from decoder: Decoder) throws {
let value = try decoder.singleValueContainer().decode(RawValue.self)
self = Self(rawValue: value) ?? Self.defaultDecoderValue
}
}
enum MediaType: String, EnumDecodable {
static let defaultDecoderValue: MediaType = .other
case audio = "AUDIO"
case multipleChoices = "MULTIPLE_CHOICES"
case other
}
如果指定了无效的enum值，也可以轻松地扩展它以抛出错误，而不是默认值。这一变化的要点可以在这里找到:https://gist.github.com/stephanecopin/4283175fabf6f0cdaf87fef2a00c8128。
使用Swift 4.1/Xcode 9.3编译和测试代码。
实际上，上面的答案真的很好，但它们遗漏了许多人在持续开发客户端/服务器项目中需要的一些细节。我们开发一个应用程序，而我们的后端随着时间不断发展，这意味着一些枚举情况将改变这种发展。因此，我们需要一个枚举解码策略，能够解码包含未知情况的枚举数组。否则，解码包含数组的对象就会失败。
我所做的很简单:
enum Direction: String, Decodable {
case north, south, east, west
}
struct DirectionList {
let directions: [Direction]
}
extension DirectionList: Decodable {
public init(from decoder: Decoder) throws {
var container = try decoder.unkeyedContainer()
var directions: [Direction] = []
while !container.isAtEnd {
// Here we just decode the string from the JSON which always works as long as the array element is a string
let rawValue = try container.decode(String.self)
guard let direction = Direction(rawValue: rawValue) else {
// Unknown enum value found - ignore, print error to console or log error to analytics service so you'll always know that there are apps out which cannot decode enum cases!
continue
}
// Add all known enum cases to the list of directions
directions.append(direction)
}
self.directions = directions
}
}
奖励:隐藏实现>使其成为一个集合
隐藏实现细节总是一个好主意。为此，您只需要再编写一点代码。诀窍是使DirectionsList符合Collection，并使你的内部列表数组私有:
struct DirectionList {
typealias ArrayType = [Direction]
private let directions: ArrayType
}
extension DirectionList: Collection {
typealias Index = ArrayType.Index
typealias Element = ArrayType.Element
// The upper and lower bounds of the collection, used in iterations
var startIndex: Index { return directions.startIndex }
var endIndex: Index { return directions.endIndex }
// Required subscript, based on a dictionary index
subscript(index: Index) -> Element {
get { return directions[index] }
}
// Method that returns the next index when iterating
func index(after i: Index) -> Index {
return directions.index(after: i)
}
}
您可以在John Sundell的这篇博客文章中阅读更多关于遵循自定义集合的内容:https://medium.com/@johnsundell/ creating-customization - colls-in swift-a344e25d0bb0
