我的主要用例是使用字典创建一个对象,例如:
struct Person: Codable { let name: String }
let dictionary = ["name": "Bob"]
let person = Person(from: dictionary)
我希望避免编写自定义实现,并尽可能高效。
目前我拥有的最佳解决方案是这个,但它需要编码/解码的额外开销。
extension Decodable {
init(from: Any) throws {
let data = try JSONSerialization.data(withJSONObject: from, options: .prettyPrinted)
let decoder = JSONDecoder()
self = try decoder.decode(Self.self, from: data)
}
}
根据问题中的例子,结果将会是:
let person = Person(from: dictionary)
如果你想要倒过来做,这可能会有所帮助:https://dev59.com/5FcO5IYBdhLWcg3wzEqf#46329055
import Foundation
enum DictionaryParsingError: Error {
case jsonSerialization(Error)
case decode(Error)
}
extension Decodable {
static func from<Key>(dictionary: [Key: Any],
options: JSONSerialization.WritingOptions = [],
decoder: JSONDecoder) -> Result<Self, DictionaryParsingError> where Key: Hashable {
let data: Data
do {
data = try JSONSerialization.data(withJSONObject: dictionary, options: options)
} catch let error {
return .failure(.jsonSerialization(error))
}
do {
return .success(try decoder.decode(Self.self, from: data))
} catch let error {
return .failure(.decode(error))
}
}
static func from<Key>(dictionary: [Key: Any],
options: JSONSerialization.WritingOptions = [],
singleUseDecoder configuration: (JSONDecoder) -> ()) -> Result<Self, DictionaryParsingError> where Key: Hashable {
let decoder = JSONDecoder()
configuration(decoder)
return from(dictionary: dictionary, options: options, decoder: decoder)
}
}
struct Item: Decodable {
let id: Int
let name: String
var date: Date
let isActive: Bool
}
let dictionary = ["id": 1,
"name": "Item",
"date": "2019-08-06T06:55:00.000-04:00",
"is_active": false] as [String : Any]
print("========================")
let decoder = JSONDecoder()
decoder.keyDecodingStrategy = .convertFromSnakeCase
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSZ"
decoder.dateDecodingStrategy = .formatted(dateFormatter)
switch Item.from(dictionary: dictionary, decoder: decoder) {
case let .failure(error): print("ERROR: \(error)")
case let .success(item): print(item)
}
print("\n========================")
let item2 = Item.from(dictionary: dictionary) { decoder in
decoder.keyDecodingStrategy = .convertFromSnakeCase
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSZ"
decoder.dateDecodingStrategy = .formatted(dateFormatter)
}
switch item2 {
case let .failure(error): print("ERROR: \(error)")
case let .success(item): print(item)
}
print("\n========================")
let item3 = Item.from(dictionary: [String:Any]()) { decoder in
decoder.keyDecodingStrategy = .convertFromSnakeCase
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSZ"
decoder.dateDecodingStrategy = .formatted(dateFormatter)
}
switch item3 {
case let .failure(error): print("ERROR: \(error)")
case let .success(item): print(item)
}
========================
Item(id: 1, name: "Item", date: 2019-08-06 10:55:00 +0000, isActive: false)
========================
Item(id: 1, name: "Item", date: 2019-08-06 10:55:00 +0000, isActive: false)
========================
ERROR: decode(Swift.DecodingError.keyNotFound(CodingKeys(stringValue: "id", intValue: nil), Swift.DecodingError.Context(codingPath: [], debugDescription: "No value associated with key CodingKeys(stringValue: \"id\", intValue: nil) (\"id\").", underlyingError: nil)))
我改编了Chris Mitchelmore的答案,使其成为可失败的初始化器,而不是抛出代码。在某些情况下更加实用。
extension Decodable {
init?(from: Any) {
guard let data = try? JSONSerialization.data(withJSONObject: from, options: .prettyPrinted) else { return nil }
let decoder = JSONDecoder()
guard let decoded = try? decoder.decode(Self.self, from: data) else { return nil }
self = decoded
}
}
.prettyPrinted
只是增加了一些不必要的开销,但它的影响应该是可以忽略不计的,因为处理JSON才是主要的性能瓶颈。 - Alex Cohn