Codable中的多个类型

Question

我使用的是API，它可以根据项目返回一个值的Bool或Int。我不熟悉如何处理Codable数据中一个值的不同类型。分级密钥可以是对象，也可以是布尔，只是不确定如何正确处理而不会出现typeMismatch错误。这是我第一次使用API遇到这种情况。

{"id":550,"favorite":false,"rated":{"value":9.0},"watchlist":false}

{“id":405,"favorite":false,"rated":false,"watchlist":false}

struct AccountState: Codable {
let id: Int?
let favorite: Bool?
let watchlist: Bool?
let rated: Rated?
}
struct Rated : Codable {
let value : Int? // <-- Bool or Int
}

Answer 1

我绝对同意@vadian的观点。你的评分是可选的。IMO这是使用propertyWrapper的完美场景。这将允许您在任何型号中使用这种额定类型，而无需手动为每个型号实现自定义编码器/解码器：

@propertyWrapper
struct RatedDouble: Codable {
var wrappedValue: Double?
init(wrappedValue: Double?) {
self.wrappedValue = wrappedValue
}
private struct Rated: Decodable {
let value: Double
}
public init(from decoder: Decoder) throws {
do {
wrappedValue = try decoder.singleValueContainer().decode(Rated.self).value
} catch DecodingError.typeMismatch {
let bool = try decoder.singleValueContainer().decode(Bool.self)
guard !bool else {
throw DecodingError.dataCorrupted(.init(codingPath: decoder.codingPath, debugDescription: "Corrupted data"))
}
wrappedValue = nil
}
}
public func encode(to encoder: Encoder) throws {
var container = encoder.singleValueContainer()
guard let double = wrappedValue else {
try container.encode(false)
return
}
try container.encode(["value": double])
}
}

---

用法：

struct AccountState: Codable {
let id: Int?
let favorite: Bool?
let watchlist: Bool?
@RatedDouble var rated: Double?
}

let json1 = #"{"id":550,"favorite":false,"rated":{"value":9.0},"watchlist":false}"#
let json2 = #"{"id":550,"favorite":false,"rated":false,"watchlist":false}"#
do {
let accountState1 = try JSONDecoder().decode(AccountState.self, from: Data(json1.utf8))
print(accountState1.rated ?? "nil")  // "9.0n"
let accountState2 = try JSONDecoder().decode(AccountState.self, from: Data(json2.utf8))
print(accountState2.rated ?? "nil")  // "niln"
let encoded1 = try JSONEncoder().encode(accountState1)
print(String(data: encoded1, encoding: .utf8) ?? "nil")
let encoded2 = try JSONEncoder().encode(accountState2)
print(String(data: encoded2, encoding: .utf8) ?? "nil")
} catch {
print(error)
}

这将打印：

9.0
nil
{观察名单"：false，"id"550，&quotquot；收藏夹"：false，quot；评级">

Answer 2

我的建议是实现init(from decoder，将rated声明为可选的Double，并解码一个Dictionary，如果解码失败，则解码一个用于密钥rated的Bool。在前一种情况下，rated被设置为Double值，在后一种情况中，它被设置为nil。

struct AccountState: Decodable {
let id: Int
let favorite: Bool
let watchlist: Bool
let rated: Double?

private enum CodingKeys: String, CodingKey { case id, favorite, watchlist, rated }

init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
id = try container.decode(Int.self, forKey: .id)
favorite = try container.decode(Bool.self, forKey: .favorite)
watchlist = try container.decode(Bool.self, forKey: .watchlist)
if let ratedData = try? container.decode([String:Double].self, forKey: .rated),
let key = ratedData.keys.first, key == "value"{
rated = ratedData[key]
} else {
let _ = try container.decode(Bool.self, forKey: .rated)
rated = nil
}
}
}

在else范围中解码Bool的行甚至可以被省略。

Answer 3

这里有一个简单的方法(很长，但很容易理解(

• 步骤1-为您的两种格式创建两种类型的结构(从您的示例中，rated可以是Bool或值为Double(

// Data will convert to this when rate is bool
struct AccountStateRaw1: Codable {
let id: Int?
let favorite: Bool?
let watchlist: Bool?
let rated: Bool?
}
// Data will convert to this when rate has value
struct AccountStateRaw2: Codable {
let id: Int?
let favorite: Bool?
let watchlist: Bool?
let rated: Rated?
struct Rated : Codable {
let value : Double?
}
}

• 第2步-创建您的AccountState，它可以容纳两种格式

// You will use this in your app, and you need the data you get from API to convert to this
struct AccountState: Codable {
let id: Int?
let favorite: Bool?
let watchlist: Bool?
let ratedValue: Double?
let isRated: Bool?
}

• 步骤3-使第1步的两个结构都能够转换为第2步的结构

protocol AccountStateConvertable {
var toAccountState: AccountState { get }
}
extension AccountStateRaw1: AccountStateConvertable {
var toAccountState: AccountState {
AccountState(id: id, favorite: favorite, watchlist: watchlist, ratedValue: nil, isRated: rated)
}
}
extension AccountStateRaw2: AccountStateConvertable {
var toAccountState: AccountState {
AccountState(id: id, favorite: favorite, watchlist: watchlist, ratedValue: rated?.value, isRated: nil)
}
}

• 最后一步-data from API-转换->structs of Steps 1—转换-->struct of Step 2

func convert(data: Data) -> AccountState? {
func decodeWith<T: Codable & AccountStateConvertable>(type: T.Type) -> AccountState? {
let parsed: T? = try? JSONDecoder().decode(T.self, from: data)
return parsed?.toAccountState
}
return decodeWith(type: AccountStateRaw1.self) ?? decodeWith(type: AccountStateRaw2.self)
}