ios - Swift 4 中带有默认大小写的 Codable 枚举

Question

我定义了一个 enum 如下:

enum Type: String, Codable {
    case text = "text"
    case image = "image"
    case document = "document"
    case profile = "profile"
    case sign = "sign"
    case inputDate = "input_date"
    case inputText = "input_text"
    case inputNumber = "input_number"
    case inputOption = "input_option"

    case unknown
}

映射一个 JSON 字符串属性。自动序列化和反序列化工作正常，但我发现如果遇到不同的字符串，反序列化失败。

是否可以定义一个映射任何其他可用案例的未知案例？

这可能非常有用，因为此数据来自 RESTFul API，将来可能会发生变化。

Answer 1

您可以扩展您的 Codable 类型并在失败时分配默认值:

enum Type: String {
    case text,
         image,
         document,
         profile,
         sign,
         inputDate = "input_date",
         inputText = "input_text" ,
         inputNumber = "input_number",
         inputOption = "input_option",
         unknown
}
extension Type: Codable {
    public init(from decoder: Decoder) throws {
        self = try Type(rawValue: decoder.singleValueContainer().decode(RawValue.self)) ?? .unknown
    }
}

---

编辑/更新:

Xcode 11.2 • Swift 5.1 或更高版本

创建一个默认为 CaseIterable & Decodable 枚举的最后一个 case 的协议(protocol):

protocol CaseIterableDefaultsLast: Decodable & CaseIterable & RawRepresentable
where RawValue: Decodable, AllCases: BidirectionalCollection { }

extension CaseIterableDefaultsLast {
    init(from decoder: Decoder) throws {
        self = try Self(rawValue: decoder.singleValueContainer().decode(RawValue.self)) ?? Self.allCases.last!
    }
}

---

Playground 测试:

enum Type: String, CaseIterableDefaultsLast {
    case text, image, document, profile, sign, inputDate = "input_date", inputText = "input_text" , inputNumber = "input_number", inputOption = "input_option", unknown
}

---

let types = try! JSONDecoder().decode([Type].self , from: Data(#"["text","image","sound"]"#.utf8))  // [text, image, unknown]