I am trying to save data from a JSON call into a variable (calling this in ViewDidLoad if it makes a difference). I've been stuck on this for quite a while and am getting pretty frustrated.
I know there are topics on this already, but I can't seem to figure it out and I'm hoping theres a simple explanation for what I'm doing wrong.
Edit: The execution goes to "print("breakpoint")" line before doing the JSON call, I'd like to force execution to wait so I can actually fill up wantedCARDSET but am struggling with how to do that. Sorry if that was unclear!
Here's the call in viewDidLoad
override func viewDidLoad() {
super.viewDidLoad()
setPickerView.dataSource = self
setPickerView.delegate = self
testJSONgrab.getCards(url: "https://mtgjson.com/json/WAR.json") {json, error in
DispatchQueue.main.async {
for item in json {
self.wantedCARDSET.append(item)
}
}
}
print("breakpoint")
getCards function
class mtgJSONDATA {
func getCards(url: String, completionHandler: #escaping ([CARDS], Error?)-> Void) {
var cardSet = [CARDS]()
guard let url = URL(string:url) else {return}
let session = URLSession.shared
let task = session.dataTask(with: url, completionHandler: {
(data, response, error) in
if error == nil {
guard let data = data else {return}
do {
let decoded = try JSONDecoder().decode(mtgJSON.self, from: data)
DispatchQueue.main.async {
for item in decoded.cards! {
cardSet.append(item)
}
completionHandler(cardSet, nil)
}
} catch let jsonError {
print("Error serializing JSON: ", jsonError)
}
}
})
task.resume()
}
You miss a reload
DispatchQueue.main.async {
self.wantedCARDSET = item
self.setPickerView.reloadAllComponents()
}
As the call to get your data is asynchronous
Related
I am facing an issue when trying to retrieve and decode JSON data from an API. I am able to get the data from the API and decode it successfully, but I can't access it from outside the function scope. I am using the following function to get and decode data. The API returns an array of JSON objects.
func getJSON(completed: #escaping () -> ()) {
var jsonData = [API_data] () // A struct for retrieved data
let url = "URL Here" // I have the original URL here, which I can't share
let task = URLSession.shared.dataTask(with: URL(string: url)!, completionHandler: { [self]data,response,error in
guard let data = data, error == nil else{
print("error")
return
}
do{
jsonData = try JSONDecoder().decode([API_data].self,from:data)
} catch{
print(error)
}
print(jsonData[0].id) // This prints my data
})
print(jsonData[0].id) // This won't print my data
task.resume()
}
struct API_data: Codable {
let id : String
}
As a result of this, I cannot use this data anywhere in the application. Any help will be appreciated. I have also tried making jsonData a global variable, updating it in the function and returning it and then using it, still doesn't work.
Thanks for your help.
As you already have a completion handler use it and pass the received data
func getJSON(completed: #escaping ([API_data]) -> Void) {
let url = "URL Here" // I have the original URL here, which I can't shar
let task = URLSession.shared.dataTask(with: URL(string: url)!) { data, _ , error in
if let error = error { print(error); return }
do {
completed(try JSONDecoder().decode([API_data].self,from:data!))
} catch{
print(error)
}
}
task.resume()
}
and use it
getJSON { apiData in
print(apiData[0].id) // This prints my data
}
Or more comfortable with the Result type
func getJSON(completed: #escaping (Result<[API_data],Error>) -> Void) {
let url = "URL Here" // I have the original URL here, which I can't shar
let task = URLSession.shared.dataTask(with: URL(string: url)!) { data, _ , error in
if let error = error { completed(.failure(error)); return }
Result { try JSONDecoder().decode([API_data].self,from: data!) }
}
task.resume()
}
getJSON { result in
switch result {
case .success(let apiData): print(apiData[0].id) // This prints my data
case .failure(let error): print(error)
}
}
It is asynchronous, you might want to access it a bit later when it’s ready, e.g. by using the completion handler.
Try creating a completion handler from your API function and send the data with the completion. And try using it there.
This question already has answers here:
Returning data from async call in Swift function
(13 answers)
Closed 1 year ago.
I'm trying to return json data from an api call. I'm able to access the json data successfully but am struggling to find a way / the best way to return it for access in my app. Thanks for any ideas!
import UIKit
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
// make the api call and obtain data
let data = self.loadData()
print("inside viewDidLoad", data) // prints 'inside viewDidLoad emptyString'
}
func loadData() -> String {
var circData = "emptyString"
let session = URLSession.shared
let url = URL(string: "https://us-east-1.aws.webhooks.mongodb-realm.com/api/client/v2.0/app/cirdata-khyvx/service/cirData/incoming_webhook/cirlAPI")!
let task = session.dataTask(with: url, completionHandler: { data, response, error in
if let json = try? JSONSerialization.jsonObject(with: data!, options: []) {
// print("json: ", json) // prints the whole json file, verifying the connection works. Some 300kb of data.
// print("json file type: ", type(of: json)) // prints '__NSArrayI'
let jsonString = "\(json)"
circData = jsonString
// print("circData", circData) // prints the whole json file, verifying that the json string has been assigned to 'circData'
}
})
task.resume()
// print("after: ", circData) // prints 'after: emptyString'. It's as if the reassignment didn't take place.
return circData
}
}
You can't return a value synchronously becuase the api call that is fetching json data is asynchronous. You need to use a completion handler instead.
You can put breakpoints in different places inside the code to understand how the flow executes.
import UIKit
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
self.loadData(completion: { [weak self] (result, error) in
if let error = error {
print(error.localizedDescription)
}
if let result = result {
print(result)
}
})
}
func loadData(completion: #escaping (_ data: Any?, _ error: Error?) -> Void) {
let url = URL(string: "https://us-east-1.aws.webhooks.mongodb-realm.com/api/client/v2.0/app/cirdata-khyvx/service/cirData/incoming_webhook/cirlAPI")!
let task = URLSession.shared.dataTask(with: url, completionHandler: { data, response, error in
if let error = error {
completion(nil, error)
return
}
do {
if let data = data {
let json = try JSONSerialization.jsonObject(with: data, options: [.allowFragments])
completion(json, nil)
} else {
completion(nil, nil)
}
} catch {
completion(nil, error)
}
})
task.resume()
}
}
so i wanna parse json api, but i the way i get that param to parse i need to fetch another json (which is working), and since i cant put that data param for my 2nd json api into global var so i can just put it into another func, i have this idea that i parse my 2nd json api inside the 1st urlSession, but i always get a nil callback,
override func viewDidLoad() {
super.viewDidLoad()
getRoom()
}
func getRoom() {
guard let url = URL(Some url) else {return}
print(url)
URLSession.shared.dataTask(with: url) { data, resp, err in
guard let data = data else {return}
do{
let decoder = JSONDecoder()
let room = try decoder.decode(User.self, from: data)
self.dataClient = [room].compactMap{$0!.data}
self.DATA = [room]
print("ini dataClient 🪕\(self.dataClient)")
let roomid = self.dataClient[0].RoomID
self.roomId = roomid
print(self.roomId)
DispatchQueue.main.async {
checkRoom()
}
}catch{
print(err!)
}
}.resume()
}
func checkRoom() {
if self.roomId == 0 {
print("roomId nil")
}else if self.roomId != 0{
print("ini room id \(self.roomId)")
guard let urlRoom = URL(some url) else {return
URLSession.shared.dataTask(with: urlRoom) { (data, resp, err) in
guard let data = data else {return}
do{
let decoder = JSONDecoder()
let roomAv = try decoder.decode(User.self, from: data)
self.DATA = [roomAv]
print("ini boolnya 🎸 \(self.DATA[0].success)")
print("Success")
}catch{
print("damn😭") // this line always get called
}
}.resume()
}
}
can anyone tell me any ideas? the reason i put the 2nd urlsession inside 1st urlsession because i need that (self.roomId) for my param in my 2nd Json api.
and when i try to separate both urlsession func in my checkRoom() alwasy called "roomId Nil"
I wouldn't make a call within a call personally. That's asking for trouble. Just call the first endpoint, get the data from it and pass in whatever you needed from that into the second call in your logic controller.
Quasi code:
import Foundation
class Test {
func getRoom() {
getFirstCall { [weak self] (foo) in
self?.getSecondCall(someArg: foo) {
// Handle data here.
}
}
}
func getFirstCall(completion: #escaping (_ somethingToReturn: String) -> ()) {
guard let url = URL(string: "Some URL") else { return }
URLSession.shared.dataTask(with: url) { data, response, error in
// Logic to ingest data.
completion("foo")
}.resume()
}
func getSecondCall(someArg: String, completion: #escaping () -> ()) {
guard let url = URL(string: "Some URL 2") else { return }
// Use "someArg" however you need in this call. queryParam, body, etc.
URLSession.shared.dataTask(with: url) { data, response, error in
// Logic to ingest data.
completion()
}.resume()
}
}
I am having problems finding out why my dataTask returns an empty result.
While going through My NetworkingManager class it appeared that it never enters the URLSession.shared.dataTask. Does anyone know why?
Her is my NetworkingManager which is being used in the ContentView of the app:
class NetworkingManager: ObservableObject {
var didChange = PassthroughSubject<NetworkingManager, Never>()
var showList = ShowResultsAPI(results: []) {
didSet {
didChange.send(self)
}
}
init() {
guard let url = URL(string: "www.json.url") else {
return }
URLSession.shared.dataTask(with: url) { (data, _, _) in
guard let data = data else {
return }
let showList = try! JSONDecoder().decode(ShowResultsAPI.self, from: data)
DispatchQueue.main.async {
self.showList = showList
}
}.resume()
}
}
In my opinion your coding looks correct.
Keep in mind that the request is asynch. When your debugging the URLSession.shared.dataTask you will recognize that at first the debugger is skipping the dataTask. When the URLSession receives a response it will enter the URLSession.shared.dataTask again.
I would recommend to set a breakpoint in the line with your guard statement. Then debug the process again and see if the debugger enters the process.
It would also be interesting to observe the response and the error in the completion handler to see if there are errors occuring.
URLSession.shared.dataTask(with: url) { (data, response, error) in
if let error = error {
print(error)
return
}
guard let httpResponse = response as? HTTPURLResponse,
httpResponse.statusCode == 200,
let data = data
else {
print("ResponseProblem")
print(response)
return
}
add return value in guard : return "example"
change your code to this :
}
}.resume()
sleep(2)
}
Adding a .sleep(2) at the end of the init() helped to process the JSON.
Edited:
It needed an asynchronous task which implies having a sleep or as #vadian suggested a better suited delay() from combine.
I'm building an iOS app in Swift 3 that's supposed to communicate with a JSON Rest Api that I'm also building myself. The app will get all sorts of content from the Api, but for now all I need it to do is check the availability of the Api through a handshake function.
let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
if error != nil {
print(error)
} else {
if let urlContent = data {
do {
let jsonResult = try JSONSerialization.jsonObject(with: urlContent, options: JSONSerialization.ReadingOptions.mutableContainers) as! NSDictionary
if jsonResult["response"] as! String == "Welcome, come in!" {
print("************ RESPONSE IS: ************")
print(jsonResult)
return
} else {
return
}
} catch {
print("************ JSON SERIALIZATION ERROR ************")
}
}
}
}
task.resume()
This is the dataTask I've set up and it runs just fine (When I print the jsonResult, I get the "Welcome!" message as expected. The problem is that I want my handshake function to return true or false (So that I can give an alert if the case is false.) When I try to set up a return true or false within the if-statement, I get the error: Unexpected non-void return value in void function.
My question is: How do I return the data out of the dataTask so that I can perform checks with it within my handshake function? I'm very new to Swift so all help is appreciated :)
Below is the entire class:
import Foundation
class RestApiManager: NSObject {
var apiAvailability:Bool?
func handshake() -> Bool {
let url = URL(string: "https://api.restaurapp.nl/handshake.php")!
let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
if error != nil {
print(error)
} else {
if let urlContent = data {
do {
let jsonResult = try JSONSerialization.jsonObject(with: urlContent, options: JSONSerialization.ReadingOptions.mutableContainers) as! NSDictionary
if jsonResult["response"] as! String == "Welcome, come in!" {
print("************ RESPONSE IS: ************")
print(jsonResult)
return true
} else {
return false
}
} catch {
print("************ JSON SERIALIZATION ERROR ************")
}
}
}
}
task.resume()
}
}
Because you're using an asynchronous API, you can't return the bool from your handshake function. If you want to show an alert in the false case, you would replace the return false with something like:
DispatchQueue.main.async {
self.showAlert()
}
Technically you could make the handshake function pause until the network stuff was done, and return the bool, but that defeats the purpose of being asynchronous, and it would freeze your app's UI during the network activity, so I doubt that's what you want to do.