can not convert json to struct object - swift

Question

I want to parse JSON data into a struct object but i can't do it.
Actually the code is in different files but here i'm posting it as a whole.
Here is my code :
import Foundation
struct dataResponse: Decodable {
var results: [userData]
init(from decoder: Decoder) throws {
var results = [userData] ()
var container = try decoder.unkeyedContainer()
while !container.isAtEnd {
if let route = try? container.decode(userData.self) {
results.append(route)
}
else {
_ = try? container.decode(dummyData.self)
}
}
self.results = results
}
}
private struct dummyData: Decodable { }
enum dataError: Error {
case dataUnavailable
case cannotProcessData
}
struct userData: Codable {
var avatar: String
var city: String
var contribution: Int
var country: String
var friendOfCount: Int
var handle: String
var lastOnlineTimeSeconds: Int
var maxRank: String
var maxRating: Int
var organization: String
var rank: String
var rating: Int
var registrationTimeSeconds: Int
var titlePhoto: String
}
struct dataRequest {
let requestUrl: URL
init(){
self.requestUrl = URL(string: "https://codeforces.com/api/user.info?handles=abhijeet_ar")!
}
func getData(completionHandler: #escaping(Result<[userData], dataError>) -> Void) {
URLSession.shared.dataTask(with: self.requestUrl) { (data,response, error) in
guard let data = data else {
completionHandler(.failure(.dataUnavailable))
print("-------bye-bye--------")
return
}
do {
print("-------entered--------")
// let dataresponse = try JSONDecoder().decode([userData].self, from: data)
// print(type(of: dataresponse))
// completionHandler(.success(dataresponse))
let jsonResult = try JSONSerialization.jsonObject(with: data, options: JSONSerialization.ReadingOptions.mutableContainers) as AnyObject
print(jsonResult)
completionHandler(.success(jsonResult as! [userData]))
}
catch {
completionHandler(.failure(.cannotProcessData))
}
}.resume()
}
}
here userData is my struct
the error says : Could not cast value of type '__NSDictionaryM' (0x7fff8fe2dab0) to 'NSArray' (0x7fff8fe2dd30).
I would appreciate if anyone helps, thanks.

Answer 1

You are making a very common mistake.
You are ignoring the root object which is a dictionary and causes the error.
struct Root: Decodable {
let status : String
let result: [UserData]
}
struct UserData: Decodable {
let avatar: String
let city: String
let contribution: Int
let country: String
let friendOfCount: Int
let handle: String
let lastOnlineTimeSeconds: Int
let maxRank: String
let maxRating: Int
let organization: String
let rank: String
let rating: Int
let registrationTimeSeconds: Int
let titlePhoto: String
}
Forget JSONSerialization and use only JSONDecoder
And it's not a good idea to return meaningless enumerated errors. Use Error and return the real error.
You get the array with dataresponse.result
struct DataRequest { // name structs always with starting capital letter
let requestUrl: URL
init(){
self.requestUrl = URL(string: "https://codeforces.com/api/user.info?handles=abhijeet_ar")!
}
func getData(completionHandler: #escaping(Result<Root, Error>) -> Void) {
URLSession.shared.dataTask(with: self.requestUrl) { (data,response, error) in
guard let data = data else {
completionHandler(.failure(error!))
print("-------bye-bye--------")
return
}
do {
print("-------entered--------")
let dataresponse = try JSONDecoder().decode(Root.self, from: data)
completionHandler(.success(dataresponse))
}
catch {
completionHandler(.failure(error))
}
}.resume()
}
}
And consider that if status is not "OK" the JSON response could be different.

Answer 2

Your problem is you are using the wrong struct. Create and use a Response struct for decoding. You need to keep your Types to have the first letter in capital to avoid confusion. You could use the JSONDecoder() maybe you are using something that doesn't have the correct format. Try the below code.
struct Response: Codable {
var result: [UserData]
}
enum DataError: Error {
case dataUnavailable, cannotProcessData
}
struct DataRequest {
let requestUrl: URL
init(){
self.requestUrl = URL(string: "https://codeforces.com/api/user.info?handles=abhijeet_ar")!
}
func getData(completionHandler: #escaping(Result<Response, DataError>) -> Void) {
URLSession.shared.dataTask(with: self.requestUrl) { (data,response, error) in
guard let data = data else {
completionHandler(.failure(.dataUnavailable))
return
}
do {
let dataresponse = try JSONDecoder().decode(Response.self, from: data)
completionHandler(.success(dataresponse))
} catch {
completionHandler(.failure(.cannotProcessData))
}
}.resume()
}
}
Note: Parameters in UserData always needs to right. Try with and Empty struct to check if everything else is working then proceed to adding the variable one-by-one.