Hello i am trying to get result based on a result from another api.The getLatest function is going to get the latest object and will return the number then i want to generate a list of urls with the latest number and then sequentially get the data in the function getXKCDData.How can i achieve this.The dispatchgroup i have on there works sometimes but doesnt work all the time because generateUrlList is called before getting the latest number and it generate the wrong url.Which causes The operation couldn’t be completed. (XKCD_Comics.NetworkError error 1.) error.How can i achieve this.
final class NetworkManager {
public static var shared = NetworkManager()
private let sessions = URLSession.shared
private func generateUrlList(latestXKCD: Int) -> [String] {
print("Here at generateUrlList")
var urls = [String]()
for i in latestXKCD-100...latestXKCD{
let xkcd_url = "https://xkcd.com/\(i)/info.0.json"
urls.append(xkcd_url)
}
return urls
}
private func getLatest(completion: #escaping(Int) -> ()){
print("Here at get latest")
guard let url = URL(string: "https://xkcd.com/info.0.json") else { return }
let task = sessions.dataTask(with: url) { data, response, error in
guard let jsonData = data else { return }
do {
let decoder = JSONDecoder()
let response = try decoder.decode(Comics.self, from: jsonData)
completion(response.num)
}catch {
completion(0)
}
}
task.resume()
}
public func getXKCDData(completion: #escaping(Result<Comics,NetworkError>) -> Void){
let group = DispatchGroup()
var latestID = 0
group.enter()
self.getLatest { (result) in
latestID = result
group.leave()
}
let urlList = generateUrlList(latestXKCD: latestID)
print(urlList)
print("Here at getXKCDData")
for url in urlList {
group.enter()
guard let url = URL(string: url) else {
completion(.failure(.InvalidURL))
return
}
let task = sessions.dataTask(with: url) { data, response, error in
guard let jsonData = data else {
completion(.failure(.NoDataAvailable))
return
}
do {
let decoder = JSONDecoder()
let response = try decoder.decode(Comics.self, from: jsonData)
completion(.success(response))
group.leave()
}catch {
completion(.failure(.CanNotProcessData))
}
}
task.resume()
}
}
}
Related
This question already has answers here:
Returning data from async call in Swift function
(13 answers)
Closed 2 years ago.
I'm coming from a JavaScript/Flutter environment and I need to await an asynchronous function in Swift. Is there a way to do it?
Basically, I want to return repoNames from a class but a "task" is executing way faster than a return keyword.
Here's the code:
import UIKit
class SearchViewModel {
let textFieldText: String?
var repoNames: Array<String> = []
init(textFieldText: String?) {
self.textFieldText = textFieldText
}
func searchForRepo() -> Array<String> {
let baseUrl = "https://api.github.com/search/repositories?q="
let finalUrl = URL(string: baseUrl + self.textFieldText!)
let session = URLSession.shared
let task = session.dataTask(with: finalUrl!) { (data, response, error) in
guard let data = data else { return }
let repos: Items = try! JSONDecoder().decode(Items.self, from: data)
for repo in repos.items {
self.repoNames.append(repo.name)
print(self.repoNames)
}
}
task.resume()
return self.repoNames
}
}
Add a completion
func searchForRepo(completion:#escaping( [String] -> ())) -> {
let baseUrl = "https://api.github.com/search/repositories?q="
let finalUrl = URL(string: baseUrl + self.textFieldText!)
URLSession.shared.dataTask(with: finalUrl!) { (data, response, error) in
guard let data = data else { return }
do {
let repos = try JSONDecoder().decode(Items.self, from: data)
self.repoNames = repos.items.map { $0repo.name }
completion(self.repoNames)
}
catch {
print(error)
}
}.resume()
}
When calling
SearchViewModel(textFieldText:"someValue").searchForRepo { res in
print(res)
}
I fetched the data and it is showing when printing but when i try to display it on tableview.Nothing is coming
Am i placing tableview.reloadData in wrong place ?
override func viewDidLoad() {
super.viewDidLoad()
fetchData()
tableView.reloadData()
}
func fetchData()
{
if let url = URL(string: urlConstant) {
let session = URLSession(configuration: .default)
let task = session.dataTask(with: url) { (data, res, err) in
if err == nil
{
let decoder = JSONDecoder()
if let safeData = data
{
do{
let results = try decoder.decode(Results.self, from: safeData)
guard let array = results.Result as? [Products] else {return }
for product in array
{
self.productArray.append(product)
}
} catch {
print(error)
}
}
}
}
task.resume()
}
self.tableView.reloadData()
}
If you are getting correct response(check it once) from the server then next thing you need to reload tableView after getting the response from the server and populating the array.
func fetchData() {
if let url = URL(string: urlConstant) {
let session = URLSession(configuration: .default)
let task = session.dataTask(with: url) { (data, res, err) in
if err == nil
{
let decoder = JSONDecoder()
if let safeData = data
{
do{
let results = try decoder.decode(Results.self, from: safeData)
guard let array = results.Result as? [Products] else {return }
for product in array {
self.productArray.append(product)
}
// Reload table view here
DispatchQueue.main.async {
self.tableView.reloadData()
}
} catch {
print(error)
}
}
}
}
task.resume()
}
}
Alternative, you can add completion handled in fetchData method.
I am trying to make an API call to the GitLab API to get the projects that are available to a particular user.
I can get one project of an index of my choosing, put it into a ProjectModel with the projectId and the projectName but I can not figure out how to get all of them into an array of ProjectModels.
By printing then I can see them all being printed in the console but it will not let me append them to an array.
It is in the parseJSON function that I am trying to get a hold of all of the projects.
Does anyone have any suggestions?
This is my manager to fetch the projects:
protocol FetchProjectsManagerDelegate {
func didUpdateProjects(_ fetchProjectsManager: FetchProjectsManager, project: ProjectModel?)
func didFailWithError(error: Error)
}
struct FetchProjectsManager {
let projectsURL = "secret"
var delegate: FetchProjectsManagerDelegate?
func fetchProjects(privateToken: String) {
let privateTokenString = "\(projectsURL)projects?private_token=\(privateToken)"
performRequest(with: privateTokenString)
}
func performRequest(with privateTokenString: String) {
// Create url
if let url = URL(string: privateTokenString) {
// Create URLSession
let session = URLSession(configuration: .default)
// Give the session a task
let task = session.dataTask(with: url) { data, response, error in
if error != nil {
self.delegate?.didFailWithError(error: error!)
return
}
if let safeData = data {
if let project = self.parseJSON(safeData) {
self.delegate?.didUpdateProjects(self, project: project)
}
}
}
// Start the task
task.resume()
}
}
func parseJSON(_ projectData: Data) -> ProjectModel? {
let decoder = JSONDecoder()
do {
let decodedData = try decoder.decode([Project].self, from: projectData)
for project in decodedData {
print(project)
}
let projectId = decodedData[0].id
let projectName = decodedData[0].name
let project = ProjectModel(projectId: projectId, projectName: projectName)
return project
} catch {
delegate?.didFailWithError(error: error)
return nil
}
}
}
This is my project model
struct ProjectModel {
let projectId: Int
let projectName: String
}
Your parseJson method only returns a single project instead of all of them, change it to
func parseJSON(_ projectData: Data) -> [ProjectModel]? {
let decoder = JSONDecoder()
do {
let decodedData = try decoder.decode([Project].self, from: projectData)
let projects = decodedData.map { ProjectModel(projectId: $0.id,
projectName: $0.name) }
return projects
} catch {
delegate?.didFailWithError(error: error)
return nil
}
}
and you of course need to update didUpdateProjects so that it takes an array of ProjectModel or call it in a loop
Trying to make a program for a news site. I take information from the site through the api, everything works fine.
The only question is, how do I get this array out of the loop?
Here is my code:
import UIKit
class ViewController: UIViewController {
var news:[News] = []
override func viewDidLoad() {
super.viewDidLoad()
getUsers()
print(news)
}
func getUsers() {
guard let url = URL(string: "http://prostir.news/swift/api2.php") else {return}
URLSession.shared.dataTask(with: url) { data, response, error in
if let data = data {
do {
news = try JSONDecoder().decode([News].self, from: data)
// print(self.news)
} catch let error {
print(error)
}
}
}.resume()
}
}
struct News:Codable, CustomStringConvertible{
let href:String?
let site:String?
let title:String?
let time:String?
var description: String {
return "(href:- \(href), site:- \(site), title:- \(title), time:- \(time))"
}
}
Declare news array in your class and assign the response to this array in getUsers method
var news:[News] = []
func getUsers(){
guard let url = URL(string: "https") else {return}
URLSession.shared.dataTask(with: url) { data, response, error in
if let data = data {
do {
self.news = try JSONDecoder().decode([News].self, from: data)
print(self.news)
} catch let error {
print(error)
}
}
}.resume()
}
The fundamental problem is you are retrieving data asynchronously (e.g. getUsers will initiate a relatively slow request from the network using URLSession, but returns immediately). Thus this won’t work:
override func viewDidLoad() {
super.viewDidLoad()
getUsers()
print(news)
}
You are returning from getUsers before the news has been retrieved. So news will still be [].
The solution is to give getUsers a “completion handler”, a parameter where you can specify what code should be performed when the asynchronous request is done:
enum NewsError: Error {
case invalidURL
case invalidResponse(URLResponse?)
}
func getUsers(completion: #escaping (Result<[News], Error>) -> Void) {
let queue = DispatchQueue.main
guard let url = URL(string: "http://prostir.news/swift/api2.php") else {
queue.async { completion(.failure(NewsError.invalidURL)) }
return
}
URLSession.shared.dataTask(with: url) { data, response, error in
if let error = error {
queue.async { completion(.failure(error)) }
return
}
guard
let data = data,
let httpResponse = response as? HTTPURLResponse,
200 ..< 300 ~= httpResponse.statusCode
else {
queue.async { completion(.failure(NewsError.invalidResponse(response))) }
return
}
do {
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .secondsSince1970
let news = try decoder.decode([News].self, from: data)
queue.async { completion(.success(news)) }
} catch let parseError {
queue.async { completion(.failure(parseError)) }
}
}.resume()
}
Then your view controller can fetch the news, passing a “closure”, i.e. code that says what to do when the asynchronous call is complete. In this case, it will set self.news and trigger the necessary UI update (e.g. maybe refresh tableview):
class ViewController: UIViewController {
var news: [News] = []
override func viewDidLoad() {
super.viewDidLoad()
fetchNews()
}
func fetchNews() {
getUsers() { result in
switch result {
case .failure(let error):
print(error)
case .success(let news):
self.news = news
print(news)
}
// trigger whatever UI update you want here, e.g., if using a table view:
//
// self.tableView.reloadData()
}
// but don't try to print the news here, as it hasn't been retrieved yet
// print(news)
}
I'm trying to fetch data from an API but I can't get it right and I don't know the issue here:
struct BTCData : Codable {
let close : Double
let high : Double
let low : Double
private enum CodingKeys : Int, CodingKey {
case close = 3
case high = 4
case low = 5
}
}
func fetchBitcoinData(completion: #escaping (BTCData?, Error?) -> Void) {
let url = URL(string: "https://api.bitfinex.com/v2/candles/trade:30m:tBTCUSD/hist")!
let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
guard let data = data else { return }
do {
if let bitcoin = try JSONDecoder().decode([BTCData].self, from: data).first {
print(bitcoin)
completion(bitcoin, nil)
}
} catch {
print(error)
}
}
task.resume()
}
I'd like to be able to access close in every dict and iterate like that:
var items : BTCData!
for idx in 0..<15 {
let diff = items[idx + 1].close - items[idx].close
upwardMovements.append(max(diff, 0))
downwardMovements.append(max(-diff, 0))
}
I get nil. I don't understand how to decode this kind of API where I need to iterate something which is not inside another dict.
EDIT: The above was solved and I'm now struggling to use [BTCData] in another function.
I am trying to use it here :
func fetchBitcoinData(completion: #escaping ([BTCData]?, Error?) -> Void) {
let url = URL(string: "https://api.bitfinex.com/v2/candles/trade:30m:tBTCUSD/hist")!
let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
guard let data = data else {
completion(nil, error ?? FetchError.unknownNetworkError)
return
}
do {
let bitcoin = try JSONDecoder().decode([BTCData].self, from: data); completion(bitcoin, nil)
//let close52 = bitcoin[51].close
//print(bitcoin)
//print(close52)
} catch let parseError {
completion(nil, parseError)
}
}
task.resume()
}
class FindArray {
var items = [BTCData]()
func findArray() {
let close2 = items[1].close
print(close2)
}
}
fetchBitcoinData() { items, error in
guard let items = items,
error == nil else {
print(error ?? "Unknown error")
return
}
let call = FindArray()
call.items = items
call.findArray()
}
EDIT 2: Solved it with [BTCData](). var items : [BTCData] = [] works too
To decode an array of arrays into a struct with Decodable you have to use unkeyedContainer. Since there is no dictionary CodingKeys are useless.
struct BTCData : Decodable {
let timestamp : Int
let open, close, high, low, volume : Double
init(from decoder: Decoder) throws {
var container = try decoder.unkeyedContainer()
timestamp = try container.decode(Int.self)
open = try container.decode(Double.self)
close = try container.decode(Double.self)
high = try container.decode(Double.self)
low = try container.decode(Double.self)
volume = try container.decode(Double.self)
}
}
You don't have to change your JSONDecoder() line.
...
if let bitcoin = try JSONDecoder().decode([BTCData].self, from: data).first {
print(bitcoin)
completion(bitcoin, nil)
}
Just by adding two lines it's even possible to decode the timestamp into a Date value
struct BTCData : Decodable {
let timestamp : Date
let open, close, high, low, volume : Double
init(from decoder: Decoder) throws {
var container = try decoder.unkeyedContainer()
timestamp = try container.decode(Date.self)
...
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .millisecondsSince1970
if let bitcoin = try decoder.decode([BTCData].self, from: data).first {
print(bitcoin)
completion(bitcoin, nil)
}
To decode the array and get a value at specific index
do {
let bitcoins = try JSONDecoder().decode([BTCData].self, from: data)
let close52 = bitcoins[51].close
print(close52)
...
You need to use JSONSerialization and cast to [[NSNumber]] to get the result needed
UPDATE
Checking this https://docs.bitfinex.com/v2/reference#rest-public-candles I think this is what you are searching for
Try using this
func fetchBitcoinData(completion: #escaping ([BTCData]?, Error?) -> Void) {
let url = URL(string: "https://api.bitfinex.com/v2/candles/trade:30m:tBTCUSD/hist")!
let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
guard let data = data else { return }
do {
if let array = try JSONSerialization.jsonObject(with: data, options: .allowFragments) as? [[NSNumber]]{
var arrayOfCoinData : [BTCData] = []
for currentArray in array{
arrayOfCoinData.append(BTCData(close: currentArray[2].doubleValue, high: currentArray[3].doubleValue, low: currentArray[4].doubleValue))
}
debugPrint(arrayOfCoinData)
completion(arrayOfCoinData, nil)
}
} catch {
print(error)
completion(nil, error)
}
}
task.resume()
}
Log Result
[BitcoinApiExample.BTCData(close: 7838.8999999999996,...]