I know it is impossible to call function from here in real app project. But in playground it was possible. What can I do now?
You can try using class
like this:
struct Dummy: Decodable {
let userId: Int
let id: Int
let title: String?
let body: String?
}
final class APIHandler{
static let shared = APIHandler()
private init () {}
func get<T: Decodable>(_ type: T.Type, completion:#escaping (Result<T,Error>)->Void) {
guard let url = URL(string:"https://jsonplaceholder.typicode.com/posts" ) else {return}
let task = URLSession.shared
task.dataTask(with: url) { data, response, error in
if let error = error {
completion(.failure(error))
}
if let data = data {
do {
let json = try JSONDecoder().decode(T.self, from: data)
completion(.success(json))
} catch let error {
print("Error with Data : \(error)")
completion(.failure(error))
}
}
}.resume()
}
}
and test it:
APIHandler.shared.get([Dummy].self) { result in
switch result {
case .success(let res):
print("response: ", res)
case .failure(let error):
print(error)
}
}
Related
I am trying to understand what is going on in my code here.
I have a simple API call to open weahter API and that whenever the user taps the UIButton, it should call the api and get the data back from open weather.
Everything works as intended however, when I have my UIButton pressed, the print statement executed first before the Task closure. I'm trying to understand the race condition here
This is my code in viewController:
#IBAction func callAPIButton(_ sender: UIButton) {
Task {
let weatherData = await weatherManager.fetchWeather(cityName: "Seattle")
}
}
Here's the code for fetching the API:
struct WeatherManager{
let weatherURL = "https://api.openweathermap.org/data/2.5/weather?appid=someAPIKeyHere"
func fetchWeather(cityName: String) -> WeatherModel? {
let urlString = "\(weatherURL)&q=\(cityName)"
let requestResult = performRequest(urlString: urlString)
return requestResult
}
func performRequest(urlString: String) -> WeatherModel? {
var weatherResult : WeatherModel? = nil
if let url = URL(string: urlString){
let session = URLSession(configuration: .default)
let task = session.dataTask(with: url, completionHandler: {
(data, response, error) in
if error != nil {
return
}
if let safeData = data {
weatherResult = parseJSON(weatherData: safeData)
}
})
task.resume()
}
return weatherResult
}
func parseJSON(weatherData: Data) -> WeatherModel?{
let decoder = JSONDecoder()
do {
let decodedData = try decoder.decode(WeatherResponse.self, from: weatherData)
print("this is in decodedData: \(decodedData)")
let temp = decodedData.main.temp
let name = decodedData.name
let weather = WeatherModel(conditionId:300, cityName: name, temperature: temp)
return weather
} catch {
print("Something is wrong here: " + error.localizedDescription)
}
return nil
}
}
Here's my Model:
struct WeatherModel{
let conditionId: Int
let cityName: String
let temperature: Double
var temperatureString: String{
return String(format: "%.1f", temperature)
}
var conditionName: String {
switch conditionId {
case 200...232:
return "cloud.bolt"
case 300...321:
return "cloud.drizzle"
case 500...531:
return "cloud.rain"
case 600...622:
return "cloud.snow"
case 701...781:
return "cloud.fog"
case 800:
return "sun.max"
case 801...804:
return "cloud.bolt"
default:
return "cloud"
}
}
}
Desired result:
This is in weatherData: WeatherResponse(name: "Seattle", weather: [Awesome_Weather_App.WeatherAPI(description: "overcast clouds", icon: "04d")], main: Awesome_Weather_App.MainAPI(temp: 287.81, pressure: 1018.0, humidity: 44.0, temp_min: 284.91, temp_max: 290.42, feels_like: 286.48), sys: Awesome_Weather_App.SysAPI(sunrise: 1.6712886e+09, sunset: 1.6713243e+09))
This is what I am getting instead:
This is in weatherData: nil
this is in decodedData: WeatherResponse(name: "Seattle", weather: [Awesome_Weather_App.WeatherAPI(description: "overcast clouds", icon: "04d")], main: Awesome_Weather_App.MainAPI(temp: 287.81, pressure: 1018.0, humidity: 44.0, temp_min: 284.91, temp_max: 290.42, feels_like: 286.48), sys: Awesome_Weather_App.SysAPI(sunrise: 1.6712886e+09, sunset: 1.6713243e+09))
Thank you in advance
Everything works as intended
No, it doesn't. I don't know why you claim such a thing; your code isn't working at all.
The problem is that you are trying to return weatherResult from performRequest. But performRequest gets its weatherResult value asynchronously, so this attempt is doomed to failure; you will always be returning nil, because the return weatherResult happens before session.dataTask ever even starts to find out what weatherResult is.
You cannot just synchronously return the results of an asynchronous request. You have two basic options for asynchronous requests.
Use the older “completion handler” pattern with Result types:
struct WeatherManager {
let weatherURL = "https://api.openweathermap.org/data/2.5/weather"
let appId = "someAPIKeyHere"
func fetchWeather(
cityName: String,
completion: #escaping (Result<WeatherModel, Error>) -> Void
) {
guard var components = URLComponents(string: weatherURL) else {
completion(.failure(URLError(.badURL)))
return
}
components.queryItems = [
URLQueryItem(name: "appid", value: appId),
URLQueryItem(name: "q", value: cityName)
]
guard let url = components.url else {
completion(.failure(URLError(.badURL)))
return
}
performRequest(url: url, completion: completion)
}
func performRequest(
url: URL,
queue: DispatchQueue = .main,
completion: #escaping (Result<WeatherModel, Error>) -> Void
) {
let session = URLSession.shared // note, do not create a new URLSession for every request or else you will leak; use shared instance
let task = session.dataTask(with: url) { data, response, error in
guard
error == nil,
let data = data,
let response = response as? HTTPURLResponse,
200 ..< 300 ~= response.statusCode
else {
queue.async { completion(.failure(error ?? URLError(.badServerResponse))) }
return
}
do {
let weatherResult = try parseJSON(weatherData: data)
queue.async { completion(.success(weatherResult)) }
} catch {
queue.async { completion(.failure(error)) }
}
}
task.resume()
}
func parseJSON(weatherData: Data) throws -> WeatherModel {
let decoder = JSONDecoder()
let response = try decoder.decode(WeatherResponse.self, from: weatherData)
print("this is in decodedData: \(response)")
return WeatherModel(conditionId: 300, cityName: response.name, temperature: response.main.temp)
}
}
Then, rather than:
let weather = weatherManager.fetchWeather(cityName: …)
You would
weatherManager.fetchWeather(cityName: …) { result in
switch result {
case .failure(let error):
print(error)
case .success(let weather):
// do something with the `weather` object here
}
}
// note, do not do anything with `weather` here, because the above
// runs asynchronously (i.e., later).
Use the newer async-await pattern of Swift concurrency:
struct WeatherManager {
let weatherURL = "https://api.openweathermap.org/data/2.5/weather"
let appId = "someAPIKeyHere"
func fetchWeather(cityName: String) async throws -> WeatherModel {
guard var components = URLComponents(string: weatherURL) else {
throw URLError(.badURL)
}
components.queryItems = [
URLQueryItem(name: "appid", value: appId),
URLQueryItem(name: "q", value: cityName)
]
guard let url = components.url else {
throw URLError(.badURL)
}
return try await performRequest(url: url)
}
func performRequest(url: URL) async throws -> WeatherModel {
let session = URLSession.shared // note, do not create a new URLSession for every request or else you will leak; use shared instance
let (data, response) = try await session.data(from: url)
guard
let response = response as? HTTPURLResponse,
200 ..< 300 ~= response.statusCode
else {
throw URLError(.badServerResponse)
}
return try parseJSON(weatherData: data)
}
func parseJSON(weatherData: Data) throws -> WeatherModel {
let decoder = JSONDecoder()
do {
let response = try decoder.decode(WeatherResponse.self, from: weatherData)
print("this is in decodedData: \(response)")
return WeatherModel(conditionId: 300, cityName: response.name, temperature: response.main.temp)
} catch {
print("Something is wrong here: " + error.localizedDescription)
throw error
}
}
}
And then you can do things like:
Task {
do {
let weather = try await weatherManager.fetchWeather(cityName: …)
// do something with `weather` here
} catch {
print(error)
}
}
Note, a few changes in the above unrelated to the asynchronous nature of your request:
Avoid creating URLSession instances. If you do, you need to remember to invalidate them. Instead, it is much easier to use URLSession.shared, eliminating this annoyance.
Avoid building URLs with string interpolation. Use URLComponents to build safe URLs (e.g., ones that can handle city names like “San Francisco”, with spaces in their names).
I have this Networking class that i declared in the Model .
class Networking {
func response (url : String ) {
guard let url = URL(string: url) else {return}
URLSession.shared.dataTask(with: url, completionHandler: urlPathCompletionHandler(data:response:error:)).resume()
}
func urlPathCompletionHandler (data : Data? , response: URLResponse? , error: Error? ) {
guard let data = data else {return }
do {
let jsondecoder = JSONDecoder()
}catch {
print("Error \(error)")
}
}
}
In the controller . I have an array of users i declared and i want the controller to call from the Model Networking class instead of doing the networking inside the controller. This is part of my controller:
var users = [Users]()
var networking : Networking()
#IBOutlet weak var tableview : UITableView!
override func viewDidLoad() {
super.viewDidLoad()
tableview.delegate = self
tableview.dataSource = self
}
func getFromModel() {
var vm = networking.response()
}
I want a way of calling the networking class and return an array of users that i can set to the users array above and use it to populate the table view . If i wanted to do that inside the controller it would easy but i am not sure how i can return an array of users from the Model Networking class .
You need to modify your Network class like this:
class Networking {
func response<T: Codable>(url: String, completion: ((T) -> Void)?) {
guard let url = URL(string: url) else {return}
URLSession.shared.dataTask(with: url, completionHandler: { (data, response, error) in
self.urlPathCompletionHandler(data: data, response: response, error: error, completion: completion)
}).resume()
}
func urlPathCompletionHandler<T: Codable>(data : Data? , response: URLResponse? , error: Error?, completion: ((T) -> Void)?) {
guard let data = data else { return }
do {
let jsondecoder = JSONDecoder()
// Pseudo Code to decode users
completion?(decodedObject)
} catch {
print("Error \(error)")
}
}
}
And call it like this:
func getFromModel() {
networking.response(url: <#T##String#>) { (users: [User]) in
self.users = users
}
}
OK, there are a few thoughts:
Your response method is performing an asynchronous network request, so you need to give it a completion handler parameter. So, I might suggest something like:
class Networking {
enum NetworkingError: Error {
case invalidURL
case failed(Data?, URLResponse?)
}
private let parsingQueue = DispatchQueue(label: Bundle.main.bundleIdentifier! + ".parsing")
// response method to handle network stuff
func responseData(_ string: String, completion: #escaping (Result<Data, Error>) -> Void) {
guard let url = URL(string: string) else {
completion(.failure(NetworkingError.invalidURL))
return
}
URLSession.shared.dataTask(with: url) { data, response, error in
DispatchQueue.main.async {
if let error = error {
completion(.failure(error))
return
}
guard
let responseData = data,
let httpResponse = response as? HTTPURLResponse,
200 ..< 300 ~= httpResponse.statusCode
else {
completion(.failure(NetworkingError.failed(data, response)))
return
}
completion(.success(responseData))
}
}.resume()
}
// response method to handle the JSON parsing
func response<T: Decodable>(of type: T.Type, from string: String, completion: #escaping (Result<T, Error>) -> Void) {
responseData(string) { result in
switch result {
case .failure(let error):
completion(.failure(error))
case .success(let data):
self.parsingQueue.async {
do {
let responseObject = try JSONDecoder().decode(T.self, from: data)
DispatchQueue.main.async {
completion(.success(responseObject))
}
} catch let parseError {
DispatchQueue.main.async {
completion(.failure(parseError))
}
}
}
}
}
}
}
This obviously assumes that you have some Codable types. For example, it’s common for an API to have some common structure in its responses:
struct ResponseObject<T: Decodable>: Decodable {
let code: Int
let message: String?
let data: T?
}
And maybe the User is like so:
struct User: Decodable {
let id: String
let name: String
}
Then getFromModel (perhaps better called getFromRepository or something like that) could parse it with:
networking.response(of: ResponseObject<[User]>.self, from: urlString) { result in
switch result {
case .failure(let error):
print(error)
case .success(let responseObject):
let users = responseObject.data
// do something with users
}
}
For what it’s worth, if you didn’t want to write your own networking code, you could use Alamofire, and then getFromModel would do:
AF.request(urlString).responseDecodable(of: ResponseObject<[User]>.self) { response in
switch response.result {
case .failure(let error):
print(error)
case .success(let responseObject):
let users = responseObject.data
}
}
Now, clearly the model types are likely to be different in your example, but you didn’t share what your JSON looked like, so I had to guess, but hopefully the above illustrates the general idea. Make a generic-based network API and give it a completion handler for its asynchronous responses.
How to use call getEmployee function while using "Result"?
struct Employee {
let name: String
let designation: String
}
func getEmployee(name: String, completion: #escaping(Result<Employee?, Error>) -> Void) {
}
First you need to make your structure conform to Codable
struct Employee: Codable {
let name, designation: String
}
Than you need to fetch your data from your server and call completion if decoding was successful with your employee .success(employee) or if it fails pass failure with your error .failure(error):
func getEmployee(name: String, completion: #escaping(Result<Employee, Error>) -> Void) {
URLSession.shared.dataTask(with: URL(string: "http://www.example.com/getEmployee.api?name=\(name)")!) { data, response, error in
guard let data = data, error == nil else {
if let error = error { completion(.failure(error)) }
return
}
do {
let employee = try JSONDecoder().decode(Employee.self, from: data)
completion(.success(employee))
} catch {
completion(.failure(error))
}
}
}
Usage:
getEmployee(name: "Ella") { result in
switch result {
case let .success(employee):
print("employee:", employee)
case let .failure(error):
print("error:", error)
default: break
}
}
I have the following issue that I'm not sure how to handle.
My JSON response can look like this:
{
"data": {
"id": 7,
"token": "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJleHAiOjE1NDY1MTU0NDMsImRhdGEiOiJ2bGFkVGVzdCIsImlhdCI6MTU0NjUwODI0M30.uwuPhlnchgBG4E8IvHvK4bB1Yj-TNDgmi7wUAiKmoVo"
},
"error": null
}
Or like this:
{
"data": [{
"id": 12
}, {
"id": 2
}, {
"id": 5
}, {
"id": 7
}],
"error": null
}
So in short the data can be either a single objet or an Array. What i have is this:
struct ApiData: Decodable {
var data: DataObject?
var error: String?
}
struct DataObject: Decodable {
var userId: Int?
enum CodingKeys: String, CodingKey {
case userId = "id"
}
}
This works fine for the first use case, but it will fail once data turns into
var data: [DataObject?]
How do I make that dynamic without duplicating code?
Edit: This is how i decode the object as well
func makeDataTaskWith(with urlRequest: URLRequest, completion: #escaping(_ apiData: ApiData?) -> ()) {
let config = URLSessionConfiguration.default
let session = URLSession(configuration: config)
session.dataTask(with: urlRequest) {
(data, response, error) in
guard let _ = response, let data = data else {return}
if let responseCode = response as? HTTPURLResponse {
print("Response has status code: \(responseCode.statusCode)")
}
do {
let retreived = try NetworkManager.shared.decoder.decode(ApiData.self, from: data)
completion(retreived)
} catch let decodeError as NSError {
print("Decoder error: \(decodeError.localizedDescription)\n")
return
}
}.resume()
}
If data can be a single object or an array write a custom initializer which decodes first an array, if a type mismatch error occurs decode a single object. data is declared as an array anyway.
As token appears only in a single object the property is declared as optional.
struct ApiData: Decodable {
let data : [DataObject]
let error : String?
private enum CodingKeys : String, CodingKey { case data, error }
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
do {
data = try container.decode([DataObject].self, forKey: .data)
} catch DecodingError.typeMismatch {
data = [try container.decode(DataObject.self, forKey: .data)]
}
error = try container.decodeIfPresent(String.self, forKey: .error)
}
}
struct DataObject: Decodable {
let userId : Int
let token : String?
private enum CodingKeys: String, CodingKey { case userId = "id", token }
}
Edit: Your code to receive the data can be improved. You should add a better error handling to return also all possible errors:
func makeDataTaskWith(with urlRequest: URLRequest, completion: #escaping(ApiData?, Error?) -> Void) {
let config = URLSessionConfiguration.default
let session = URLSession(configuration: config)
session.dataTask(with: urlRequest) {
(data, response, error) in
if let error = error { completion(nil, error); return }
if let responseCode = response as? HTTPURLResponse {
print("Response has status code: \(responseCode.statusCode)")
}
do {
let retreived = try NetworkManager.shared.decoder.decode(ApiData.self, from: data!)
completion(retreived, nil)
} catch {
print("Decoder error: ", error)
completion(nil, error)
}
}.resume()
}
Using power of generic, it simple like below:
struct ApiData<T: Decodable>: Decodable {
var data: T?
var error: String?
}
struct DataObject: Decodable {
private var id: Int?
var userId:Int? {
return id
}
}
Use
if let obj = try? NetworkManager.shared.decoder.decode(ApiData<DataObject>.self, from: data) {
//Do somthing
} else if let array = try NetworkManager.shared.decoder.decode(ApiData<[DataObject]>.self, from: data) {
// Do somthing
}
If you have only two possible outcomes for your data, an option would be to try and parse data to one of the expected types, if that fails you know that the data is of other type and you can then handle it accordingly.
See this
You can try
struct Root: Codable {
let data: DataUnion
let error: String?
}
enum DataUnion: Codable {
case dataClass(DataClass)
case datumArray([Datum])
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
if let x = try? container.decode([Datum].self) {
self = .datumArray(x)
return
}
if let x = try? container.decode(DataClass.self) {
self = .dataClass(x)
return
}
throw DecodingError.typeMismatch(DataUnion.self, DecodingError.Context(codingPath: decoder.codingPath, debugDescription: "Wrong type for DataUnion"))
}
func encode(to encoder: Encoder) throws {
var container = encoder.singleValueContainer()
switch self {
case .dataClass(let x):
try container.encode(x)
case .datumArray(let x):
try container.encode(x)
}
}
}
struct Datum: Codable {
let id: Int
}
struct DataClass: Codable {
let id: Int
let token: String
}
let res = try? JSONDecoder().decode(Root.self, from:data)
I successfully fetched and decoded data from an API and now have access to all the data I need to be used in the algorithm I want to write in my App.
The issue is that I don't know how to access this data after I decoded it, I can print it immediately after it's decoded but I have no idea how to use it in another function or place in my app.
Here is my Playground:
import PlaygroundSupport
PlaygroundPage.current.needsIndefiniteExecution = true
enum MyError : Error {
case FoundNil(String)
}
struct Level: Codable {
let time: Double
let close: Double
let high: Double
let low: Double
let open: Double
}
struct Response: Codable {
let data: [Level]
private enum CodingKeys : String, CodingKey {
case data = "Data"
}
}
func fetchData(completion: #escaping (Response?, Error?) -> Void) {
let url = URL(string: "https://min-api.cryptocompare.com/data/histominute?fsym=BTC&tsym=USD&limit=60&aggregate=3&e=CCCAGG")!
let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
guard let data = data else { return }
do {
if let marketData = try? JSONDecoder().decode(Response.self, from: data) {
print(marketData.data[0].open)
print(marketData.data[1].open)
print("Average=", (marketData.data[0].open + marketData.data[1].open) / 2)
//completion(marketData, nil)
throw MyError.FoundNil("data")
}
} catch {
print(error)
}
}
task.resume()
}
fetchData() { items, error in
guard let items = items,
error == nil else {
print(error ?? "Unknown error")
return
}
print(items)
}
How can I use .data[0], .data[1], ..., somewhere else?
You data will be available in your fecthData() call. Probably what you want is your items variable, where you're printing it. But make sure to call the completion in your fetchData implementation.
WARNING: Untested code.
import PlaygroundSupport
PlaygroundPage.current.needsIndefiniteExecution = true
enum MyError: Error {
case FoundNil(String)
case DecodingData(Data)
}
struct Level: Codable {
let time: Double
let close: Double
let high: Double
let low: Double
let open: Double
}
struct Response: Codable {
let data: [Level]
private enum CodingKeys : String, CodingKey {
case data = "Data"
}
}
func fetchData(completion: #escaping (Response?, Error?) -> Void) {
let url = URL(string: "https://min-api.cryptocompare.com/data/histominute?fsym=BTC&tsym=USD&limit=60&aggregate=3&e=CCCAGG")!
let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
guard let data = data else {
completion(nil, MyError.FoundNil("data"))
}
do {
if let marketData = try? JSONDecoder().decode(Response.self, from: data) {
completion(marketData, nil)
} else {
completion(nil, MyError.DecodingData(data)) // work on this duplicated call
}
} catch {
completion(nil, MyError.DecodingData(data)) // work on this duplicated call
}
}
task.resume()
}
fetchData() { items, error in
if let error == error {
switch(error) {
case .foundNil(let whatsNil):
print("Something is nil: \(whatsNil)")
case .decodingData(let data):
print("Error decoding: \(data)")
}
} else {
if let items = items {
print(items.data[0].open)
print(items.data[1].open)
print("Average=", (items.data[0].open + items.data[1].open) / 2)
print(items)
} else {
print("No items to show!")
}
}
}
I don't understand what is your real issue, because you have written everything you need here, but as far I understand , to pass data
just uncomment this line completion(marketData, nil)
and in
fetchData() { items, error in
guard let items = items,
error == nil else {
print(error ?? "Unknown error")
return
}
print(items)
}
items is an object of your struct Response. You can pass this anywhere in your other class , by just creating an another variable like:
var items : Response!
for example :
class SomeOtherClass : NSObject{
var items : Response!
func printSomeData()
{
print(items.data[0].open)
print(items.data[1].open)
print("Average=", (items.data[0].open + items.data[1].open) / 2)
}
}
and in fetchData method write this:
fetchData() { items, error in
guard let items = items,
error == nil else {
print(error ?? "Unknown error")
return
}
let otherObject = SomeOtherClass()
otherObject.items = items
otherObject.printSomeData()
}