How to save data from Json with Alamofire and SwiftyJSON? - ios

Question

I am trying to save "author" data to global variable named "authors" from json(Link:"https://learnappmaking.com/ex/books.json") with these two libraries. But it only works at the trailing closure of func Alamofire.request(url).responseJSON. When I access the global variable named "authors" from somewhere except the trailing closure, what I get is an empty array of string.
Can someone explain the reason behind this werid situation？
Thanks a lot.
class ViewController: UIViewController {
var authors = [String]()
let url = "https://learnappmaking.com/ex/books.json"
func getAuthorsCount() {
print("the number of authors : \(authors.count)") // I hope that here, the number of authors should be 3 too! actually, it is 0. Why?
// this for loop doesn't get excuted
for author in authors {
print(author)
}
}
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
Alamofire.request(url).responseJSON { response in
if let data = response.data {
if let json = try? JSON(data: data) {
for item in json["books"].arrayValue {
var outputString: String
print(item["author"])
outputString = item["author"].stringValue
//urlOfProjectAsset.append(outputString)
self.authors.append(outputString)
print("authors.count: \(self.authors.count)")
}
}
}
}
getAuthorsCount()
print("-------------")
}
}
the actual output is:
Update：
I adjusted my code:
class ViewController: UIViewController {
var authors = [String]()
let url = "https://learnappmaking.com/ex/books.json"
func getAuthorsCount() {
print("the number of authors : \(authors.count)")
// this for loop doesn't get excuted
for author in authors {
print(author)
}
}
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
Alamofire.request(url).responseJSON { response in
if let data = response.data {
if let json = try? JSON(data: data) {
for item in json["books"].arrayValue {
var outputString: String
//print(item["author"])
outputString = item["author"].stringValue
//urlOfProjectAsset.append(outputString)
self.authors.append(outputString)
//print("authors.count: \(self.authors.count)")
}
self.getAuthorsCount() // I added this line of code.
}
}
}
getAuthorsCount()
print("-------------")
}
}
But why does the func getAuthorsCount() (not self. version) still print an empty array of strings ? I think the result should be the same as the result which
func self.getAuthorsCount() printed.
I am so confused now...
Again, I want to use the data kept in the variable named "authors", but what I only got is an empty array of strings.

Answer 1

I'll try to answer all your questions :
The data is persistant
You are doing the following : Alamo.request (Network call) -> getAuthors(print result - empty) ->
response (receive response) -> self.authors.append(save response) -> self.authors (print result)
You need to do : Alamo.request (Network call) -> response (receive response) -> self.authors.append(save response) -> self.getAuthors or getAuthors(same) (inside the response {})
You need to call getAuthors once you have your result, inside the response callback :
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
Alamofire.request(url).responseJSON { response in
if let data = response.data {
if let json = try? JSON(data: data) {
for item in json["books"].arrayValue {
var outputString: String
print(item["author"])
outputString = item["author"].stringValue
//urlOfProjectAsset.append(outputString)
self.authors.append(outputString)
print("authors.count: \(self.authors.count)")
}
self.getAuthorsCount()
print("-------------")
//Do whatever you want from here : present/push
}
}
}
Then you can use the saved data :
To send the data to another ViewController you can use various methods (present/push, closure/callback, ...)
Usually you will have a loading spinner to wait for the network to
answer then you will show your next controller

Answer 2

As requested via direct message: a Swift-only approach. Just paste this in a blank Playground:
import Foundation
final class NetworkService {
enum ServiceError: LocalizedError {
case invalidUrl
case networkingError(error: Error)
case parsingError
var localizedDescription: String? { return String(describing: self) }
}
func request(completion: #escaping (Result<[UserObject], Error>) -> Void ) {
guard let url = URL(string: "https://jsonplaceholder.typicode.com/users") else {
completion(.failure(ServiceError.invalidUrl))
return
}
let dataTask = URLSession.shared.dataTask(with: url) { (jsonData, response, error) in
if let jsonData = jsonData {
let jsonDecoder = JSONDecoder()
do {
let users = try jsonDecoder.decode([UserObject].self, from: jsonData)
completion(.success(users))
} catch {
completion(.failure(ServiceError.parsingError))
}
} else if let error = error {
completion(.failure(ServiceError.networkingError(error: error)))
}
}
dataTask.resume()
}
}
struct UserObject: Codable {
let id: Int
let name: String
let username: String
let email: String?
let website: String?
}
let networkService = NetworkService()
networkService.request { result in
switch result {
case .success(let users):
debugPrint("Received \(users.count) users from REST API")
debugPrint(users)
case .failure(let error):
debugPrint(error.localizedDescription)
}
}