用Swift解码JSON数据时出现问题

Question

试图在解码JSON数据方面进行一些练习，遇到了一个问题。我知道URL是有效的，但由于某种原因，我的解码器不断抛出错误。下面是我的模型结构，我试图解码的JSON对象，以及我的解码器。

型号结构：

struct Event: Identifiable, Decodable {
let id: Int
let description: String
let title: String
let timestamp: String
let image: String
let phone: String
let date: String
let locationline1: String
let locationline2: String
}
struct EventResponse: Decodable {
let request: [Event]
}

JSON响应：

[
{
"id": 1,
"description": "Rebel Forces spotted on Hoth. Quell their rebellion for the Empire.",
"title": "Stop Rebel Forces",
"timestamp": "2015-06-18T17:02:02.614Z",
"image": "https://raw.githubusercontent.com/phunware-services/dev-interview-homework/master/Images/Battle_of_Hoth.jpg",
"date": "2015-06-18T23:30:00.000Z",
"locationline1": "Hoth",
"locationline2": "Anoat System"
},
{
"id": 2,
"description": "All force-sensitive members of the Empire must report to the Sith Academy on Korriban. Test your passion, attain power, to defeat your enemy on the way to becoming a Dark Lord of the Sith",
"title": "Sith Academy Orientation",
"timestamp": "2015-06-18T21:52:42.865Z",
"image": "https://raw.githubusercontent.com/phunware-services/dev-interview-homework/master/Images/Korriban_Valley_TOR.jpg",
"phone": "1 [phone]",
"date": "2015-09-27T15:00:00.000Z",
"locationline1": "Korriban",
"locationline2": "Horuset System"
},
{
"id": 3,
"description": "There is trade dispute between the Trade Federation and the outlying systems of the Galactic Republic, which has led to a blockade of the small planet of Naboo. You must smuggle supplies and rations to citizens of Naboo through the blockade of Trade Federation Battleships",
"title": "Run the Naboo Blockade",
"timestamp": "2015-06-26T03:50:54.161Z",
"image": "https://raw.githubusercontent.com/phunware-services/dev-interview-homework/master/Images/Blockade.jpg",
"phone": "1 [phone]",
"date": "2015-07-12T19:08:00.000Z",
"locationline1": "Naboo",
"locationline2": "Naboo System"
}
]

我的解码器：

func getEvents(completed: @escaping (Result<[Event], APError>) -> Void) {
guard let url = URL(string: eventURL) else {
completed(.failure(.invalidURL))
return
}

let task = URLSession.shared.dataTask(with: URLRequest(url: url)) { data, response, error in

if let _ =  error {
completed(.failure(.unableToComplete))
return
}

guard let response = response as? HTTPURLResponse, response.statusCode == 200 else {
completed(.failure(.invalidResponse))
return
}

guard let data = data else {
completed(.failure(.invalidData))
return
}

do {
let decoder = JSONDecoder()
let decodedResponse = try decoder.decode(EventResponse.self, from: data)
completed(.success(decodedResponse.request))
} catch {
completed(.failure(.invalidData))
}
}

task.resume()
}

我相信答案对一些人来说是显而易见的，但我一直在碰壁。谢谢

Answer 1

EventResponse建议JSON的形式为：

{
"request": [...]
}

但这显然不是JSON所包含的内容。

但你可以替换：

let decodedResponse = try decoder.decode(EventResponse.self, from: data)

带有：

let decodedResponse = try decoder.decode([Event].self, from: data)

并且不再需要EventResponse类型。

---

FWIW，在catch块中，返回.invalidData错误。但是decode(_:from:)抛出的错误包含有关解析问题的含义信息。我建议捕获/显示原始错误，因为它会告诉你它失败的确切原因。在catch块中打印错误消息，或者将原始错误作为相关值包含在invalidData错误中。但目前，您正在丢弃decode(_:from:)抛出的错误中包含的所有有用信息。

---

不相关，但您可以将Event更改为使用URL和Date类型：

struct Event: Identifiable, Decodable {
let id: Int
let description: String
let title: String
let timestamp: Date
let image: URL
let phone: String
let date: Date
let locationline1: String
let locationline2: String
}

并配置您的日期格式，为您解析这些日期：

let formatter = DateFormatter()
formatter.locale = Locale(identifier: "en_US_POSIX")
formatter.timeZone = TimeZone(secondsFromGMT: 0)    // not necessary because you have timezone in the date string, but useful if you ever use this formatter with `JSONEncoder`
formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSX"
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .formatted(formatter)

---

如果您想让Swift代码遵循camelBase命名惯例，即使API没有，您也可以手动指定您的编码密钥：

struct Event: Identifiable, Decodable {
let id: Int
let description: String
let title: String
let timestamp: Date
let image: URL
let phone: String
let date: Date
let locationLine1: String
let locationLine2: String
enum CodingKeys: String, CodingKey {
case id, description, title, timestamp, image, phone, date
case locationLine1 = "locationline1"
case locationLine2 = "locationline2"
}
}