Accessing data after calling an API - swift

Question

first, I'm very (very) new to Swift programming. Challenging but so interesting!
Right now, in a Playground, I'm trying to fetch the data from a JSON that I can access using a URL.
I need to store the data somewhere (in this case I need to store an array of BixiStationViewModel so I can later on play with the data I fetch from the URL.
I think the issue is coming from the asynchronous process that is fetching the data and then having my code processing it.
You can see at the end of the code the print(allBixi.allStations) statement: it returns an empty array.
import Foundation
// JSON structure
struct BixiStationDataModel: Codable {
let lastUpdated, ttl: Int?
let data: StationsData?
enum CodingKeys: String, CodingKey {
case lastUpdated = "last_updated"
case ttl, data
}
}
struct StationsData: Codable {
let stations: [StationData]?
}
struct StationData: Codable {
let stationID: String?
let numBikesAvailable, numEbikesAvailable, numBikesDisabled, numDocksAvailable: Int?
let numDocksDisabled, isInstalled, isRenting, isReturning: Int?
let lastReported: Int?
let eightdHasAvailableKeys: Bool?
let eightdActiveStationServices: [EightdActiveStationService]?
enum CodingKeys: String, CodingKey {
case stationID = "station_id"
case numBikesAvailable = "num_bikes_available"
case numEbikesAvailable = "num_ebikes_available"
case numBikesDisabled = "num_bikes_disabled"
case numDocksAvailable = "num_docks_available"
case numDocksDisabled = "num_docks_disabled"
case isInstalled = "is_installed"
case isRenting = "is_renting"
case isReturning = "is_returning"
case lastReported = "last_reported"
case eightdHasAvailableKeys = "eightd_has_available_keys"
case eightdActiveStationServices = "eightd_active_station_services"
}
}
struct EightdActiveStationService: Codable {
let id: String?
}
// Calling the API
class WebserviceBixiStationData {
func loadBixiStationDataModel(url: URL, completion: #escaping ([StationData]?) -> ()) {
URLSession.shared.dataTask(with: url) { data, response, error in
guard let data = data, error == nil else {
completion(nil)
return
}
let response = try? JSONDecoder().decode(BixiStationDataModel.self, from: data)
if let response = response {
DispatchQueue.main.async {
completion(response.data?.stations)
}
}
}.resume()
}
}
// Data Model
class BixiStationViewModel {
let id = UUID()
let station: StationData
init(station: StationData) {
self.station = station
}
var stationID: String {
return self.station.stationID ?? ""
}
var numBikesAvailable: Int {
return self.station.numBikesAvailable ?? 0
}
var numDocksAvailable: Int {
return self.station.numDocksAvailable ?? 0
}
var isInstalled: Int {
return self.station.isInstalled ?? 0
}
var isReturning: Int {
return self.station.isReturning ?? 0
}
}
class BixiStationListModel {
init() { fetchBixiApiDataModel() }
var allStations = [BixiStationViewModel]()
private func fetchBixiApiDataModel() {
guard let url = URL(string: "https://api-core.bixi.com/gbfs/en/station_status.json") else {
fatalError("URL is not correct")
}
WebserviceBixiStationData().loadBixiStationDataModel(url: url) { stations in
if let stations = stations {
self.allStations = stations.map(BixiStationViewModel.init)
}
}
}
}
// Checking if the data has been dowloaded
let allBixi = BixiStationListModel()
print(allBixi.allStations)
How can I fix the code so I could access the values in the var allStations = [BixiStationViewModel]()
Thanks in advance, I've Benn working on it this issue for a while now and this would help me a lot in my app development

Answer 1

In a playground you need continuous execution to work with a url response.
Add PlaygroundPage.current.needsIndefiniteExecution = true to the top of your file (doesn't matter where it's added but I always do the top)
To get your data to print, add a print statement inside your loadBixiStationDataModel callback
WebserviceBixiStationData().loadBixiStationDataModel(url: url) { stations in
if let stations = stations {
self.allStations = stations.map(BixiStationViewModel.init)
print(stations)
}
}