在 Swift 5 中解码 JSON 后得到 nil

Question

@Edit - Thanks to the do-try-catch suggestion from Finn, it turned out Json was containing some null values, which I had missed during testing in postman. After refactoring fields in UserInfoStruct to Optionals, everything works.

I'm trying to unwrap json in my application, but despite getting code 200 from server and receiving bytes of data, printing returns nil . Putting field in struct that returns string with all the information resulted with nil as well, same with printing one of the fields. I've followed tutorials like the one on hackingwithswift.com, but to no avail. Previously checking on reqres.in endpoints, everything works just fine.

Code used to fetch data from api with the build-in json decoder:

func getUserInfo() {
        var userInfo: UserInfoStruct?
        let token = UserDefaults.standard.string(forKey: ApiUtils().userToken) ?? ""
        guard let url = URL(string: EndpointUrls().machineUrl + EndpointUrls().profileUrl) else { return }
        var request = URLRequest(url: url)
        request.httpMethod = HttpMethodsStruct().get
        request.setValue(ApiUtils().appjson, forHTTPHeaderField: ApiUtils().contType)
        request.addValue(ApiUtils().bearer + token, forHTTPHeaderField: ApiUtils().auth)
        URLSession.shared.dataTask(with: request) {data, response, error in
            let httpStatusCode = (response as? HTTPURLResponse)?.statusCode ?? 0
            print(httpStatusCode)
            if (httpStatusCode) == 200 {
                if let data = data {
                    print(data)
                    userInfo = try? JSONDecoder().decode(UserInfoStruct.self, from: data)
                    print(userInfo)
                }
            }
        }.resume()
    }

I've replaced all the strings with variables declared in another struct, as some of them are used in the more places. With this, any changes would be easier to implement. To access the endpoints, You need to be logged in a specific vpn.

Here is the example json I'm receiving:

{
  "authorities": [
    {
      "created_at": "2021-01-21T13:49:32.755Z",
      "id": 0,
      "name": "string",
      "updated_at": "2021-01-21T13:49:32.755Z"
    }
  ],
  "business_name": "string",
  "created_at": "2021-01-21T13:49:32.755Z",
  "devices_limit": 0,
  "email": "string",
  "first_name": "string",
  "has_active_call": true,
  "id": 0,
  "is_business_account": true,
  "last_name": "string",
  "marketing": true,
  "min_to_call": 0,
  "paid_to": "2021-01-21T13:49:32.755Z",
  "password_reset_active_link": true,
  "phone_number": "string",
  "translation_types": [
    {
      "display_name": "string",
      "id": 0,
      "jabber_destination": "string",
      "name": "string"
    }
  ],
  "updated_at": "2021-01-21T13:49:32.755Z"
}

Using app.quicktype.io, following structs has been generated:

import Foundation

struct UserInfoStruct: Codable {
    let authorities: [Authority]
    let business_name: String
    let created_at: String
    let devices_limit: Int
    let email: String
    let first_name: String
    let has_active_call: Bool
    let id: Int
    let is_business_account: Bool
    let last_name: String
    let marketing: Bool
    let min_to_call: Int
    let paid_to: String
    let password_reset_active_link: Bool
    let phone_number: String
    let translation_types: [TranslationType]
    let updated_at: String
}

struct Authority: Codable {
    let created_at: String
    let id: Int
    let name: String
    let updated_at: String
}

struct TranslationType: Codable {
    let display_name: String
    let id: Int
    let jabber_destination: String
    let name: String
}

Still, in console all, that's printed, is this:

200        <- from print(httpStatusCode)
689 bytes  <- from print(data)
nil        <- from print(userInfo)

As in some tutorials, I've tried to declare userInfo field as

var userInfo = [UserInfoStruct]()

but it only resulted in

Cannot assign value of type 'UserInfoStruct?' to type '[UserInfoStruct]'

Declaring this field both in the func as well as @State in the main struct gave the same results.

About me: I'm self-taught with background in java. I've been developing in swift since October 2020, so I'm fully aware, that many problems might be trivial and my lack of experience causes me to miss them.

Thanks for all the help.

Answer 1

You can try catching your errors with a do-catch block instead of just using try? . This will enable you to log a error message instead if just getting a nil result.

a do-catch block is formed like this:

do {
    userInfo = try JSONDecoder().decode(UserInfoStruct.self, from: data)
    print("Success!")
} catch {
    print("Unexpected error: \(error).")
}