cannot make post request in swift 4 - json

Question

cannot men a POST request but cannot understand why, the struct is Codable and there is no erro in url. I get this message error in console
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** +[NSJSONSerialization dataWithJSONObject:options:error:]: Invalid top-level type in JSON write'
*** First throw call stack:
(0x1ac0dfea0 )
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb)
but everything seems to be ok
my struct:
struct PostOfMine: Codable {
let body: String?
let id: Int?
let title: String?
let userId: Int?
}
my func:
func postData() {
guard let url = URL(string: "https://jsonplaceholder.typicode.com/posts") else {
print("WARNING: url related error")
return}
var request = URLRequest(url: url)
request.httpMethod = "POST"
request.addValue("Application/json", forHTTPHeaderField: "Content-Type")
let newPost = PostOfMine(body: "test body", id: 20, title: "test title", userId: 20)
do {
let jsonBody = try JSONSerialization.data(withJSONObject: newPost, options: [])
request.httpBody = jsonBody
} catch {
print(error.localizedDescription)
}
let session = URLSession.shared
let task = session.dataTask(with: request) { (Data, _, error) in
guard let data = Data else {return}
do {
let sentPost = try JSONSerialization.jsonObject(with: data, options: [])
print(sentPost)
} catch {
print(error.localizedDescription)
}
}
task.resume()
}

Answer 1

As per apple documents:
JSONSerialization.data(withJSONObject: obj, options: [])
If obj will not produce valid JSON, an exception is thrown. This exception is thrown prior to parsing and represents a programming error, not an internal error. You should check whether the input will produce valid JSON before calling this method by using isValidJSONObject(_:).
In your code exception is raised due to below reason
JSONSerialization.data(withJSONObject: obj, options: [])
In this method you have to pass the valid JSON object e.g obj. You are just confirming to the codable protocol and passing the structure variable instead of JSON object.
Code:
struct PostOfMine: Codable {
let body: String?
let id: Int?
let title: String?
let userId: Int?
private enum CodingKeys: String, CodingKey {
case body
case id
case title
case userId
}
func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: CodingKeys.self)
try container.encode(body, forKey: .body)
try container.encode(id, forKey: .id)
try container.encode(title, forKey: .title)
try container.encode(userId, forKey: .userId)
}
}
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
let newPost = PostOfMine(body: "test body", id: 20, title: "test title", userId: 20)
do {
let encoder = JSONEncoder()
let newPostData = try encoder.encode(newPost)
//Send newPostData to your server.
request.httpBody = newPostData
//Send data you your server
//For Decoding the data use JSONDecoder
let post = try JSONDecoder().decode(PostOfMine.self, from: newPostData)
debugPrint(post)
} catch {
debugPrint(error.localizedDescription)
}
}

Answer 2

Since your model conforms to Codable you get JSONEncoder().encode(_:) for free. Use that to encode instead of JSONSerialization
func postData() {
//...
//For this particular api, the server will take care of generating an `id` so leave that as `nil`
let newPost = PostOfMine(body: "test body", id: nil, title: "test title", userId: 20)
do {
let jsonBody = try JSONEncoder().encode(newPost)
} catch {
print(error.localizedDescription)
}
let session = URLSession.shared
session.dataTask(with: request) { _, response, error in
if error != nil {
//check & handle error from upload task.
}
if let response = response as? HTTPURLResponse {
// Monitor the status code recieved from the server. 200-300 = OK
print(response.statusCode)
// prints 201 - Created
}
}.resume()
}