ios - 使具有关联值的枚举符合可解码？

Question

我试图使具有不同关联值的枚举符合 Decodable 协议(protocol)，但在关联值部分遇到问题。

enum SportType: Decodable {
    case team(String, String) //Two team names
    case individual([String]) //List of player names
}

我已经成功获得了一个符合 Decodable 的枚举，但没有关联值，但在使用关联值做同样的事情时遇到了困难。

//Works but no associated values
enum SportType: String, Decodable {
    case team, case individual
}

Answer 1

您需要创建一个自定义 init(from detector: Decoder) throws，并将关联值视为对象中的普通字段，使用 CodingKeys 进行解码他们。详细信息取决于关联值在编码对象中的实际表示方式。

例如，如果您的值编码为:

{ "team1": "aaa", "team2": "bbb" }

和

{ "individual": ["x", "y", "z"]}

你可以:

enum SportType: Decodable {

    case team(String, String) //Two team names
    case individual([String]) //List of player names

    // Define associated values as keys
    enum CodingKeys: String, CodingKey {
        case team1
        case team2
        case individual
    }

    init(from decoder: Decoder) throws {

        let container = try decoder.container(keyedBy: CodingKeys.self)

        // Try to decode as team
        if let team1 = try container.decodeIfPresent(String.self, forKey: .team1),
           let team2 = try container.decodeIfPresent(String.self, forKey: .team2) {
            self = .team(team1, team2)
            return
        }

        // Try to decode as individual
        if let individual = try container.decodeIfPresent([String].self, forKey: .individual) {
            self = .individual(individual)
            return
        }

        // No luck
        throw DecodingError.dataCorruptedError(forKey: .individual, in: container, debugDescription: "No match")
    }
}

测试:

let encoded = """
    { "team1": "aaa", "team2": "bbb" }
""".data(using: .utf8)

let decoded = try? JSONDecoder().decode(SportType.self, from: encoded!)

switch decoded {
case .team(let a, let b):
    print("I am a valid team with team1=\(a), team2=\(b)")
case .individual(let a):
    print("I am a valid individual with individual=\(a)")
default:
    print("I was not parsed :(")
}

打印:

I am a valid team with team1=aaa, team2=bbb