Parsing JSON returns nil, why? - ios

Question

This is my first project working with JSON, so this question could probably be relevant to others in the same situation.
I'm making a weather app using the DarkSky API. So far, I'm requesting the data from the internet, parsing it and, for testing, printing it in the console. Unfortunately, I just get nil. Here's the relevant code:
-> Functions in my ViewController:
func getWeatherData(latitude: String, longitude: String, time: String) {
let basePath = "https://api.darksky.net/forecast/xxxxxxxxxxxxxxxb170/"
let url = basePath + "\(latitude),\(longitude)"
let request = URLRequest(url: URL(string: url)!)
let task = URLSession.shared.dataTask(with: request) {
(data:Data?, response:URLResponse?, error:Error?)
in
if let data = data {
do {
if let json = try JSONSerialization.jsonObject(with: data, options: []) as? [String:Any] {
let dictionary = json
UserDefaults.standard.set(dictionary, forKey: "lastWeatherUpdate")
}
} catch {
print(error.localizedDescription)
}
}
}
}
func getCurrentWeather() {
getWeatherData(latitude: "37", longitude: "40", time: "40000")
let weather = UserDefaults.standard.dictionary(forKey: "lastWeatherUpdate")
print(weather?["latitude"])
}
Does someone spot my mistake? Here's how DarkSky specifies the structure of the JSON data:
"latitude": 47.20296790272209,
"longitude": -123.41670367098749,
"timezone": "America/Los_Angeles",
"currently": {
"time": 1453402675,
"summary": "Rain",
"icon": "rain",
"nearestStormDistance": 0,
"precipIntensity": 0.1685,
"precipIntensityError": 0.0067,
"precipProbability": 1,
"precipType": "rain",
"temperature": 48.71,
"apparentTemperature": 46.93,
"dewPoint": 47.7,
"humidity": 0.96,
"windSpeed": 4.64,
"windGust": 9.86,
"windBearing": 186,
"visibility": 4.3,
"cloudCover": 0.73,
"pressure": 1009.7,
"ozone": 328.35
Well, apparently that's just the important part of the JSON.
Can anyone spot my mistake?

Answer 1

Does someone spot my mistake?
Actually there are two mistakes:
As mentioned in the comments the task must be resumed
dataTask works asynchronously, it requires a completion handler to be able to print something after the call.
The code uses a simple enum with associated types as return type for convenience reasons.
enum WeatherResult {
case success([String:Any]), failure(Error)
}
func getWeatherData(latitude: String, longitude: String, time: String, completion: #escaping (WeatherResult)->()) {
let basePath = "https://api.darksky.net/forecast/xxxxxxxxxxxxxxxb170/"
let urlString = basePath + "\(latitude),\(longitude)"
let url = URL(string: urlString)!
let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
if let error = error {
completion(.failure(error))
return
}
do {
if let json = try JSONSerialization.jsonObject(with: data!) as? [String:Any] {
completion(.success(json))
} else {
completion(.failure(NSError(domain: "myDomain", code: 1, userInfo: [NSLocalizedDescriptionKey : "JSON is not a dictionary"])))
}
} catch {
completion(.failure(error))
}
}
task.resume()
}
func getCurrentWeather() {
getWeatherData(latitude: "37", longitude: "40", time: "40000") { result in
switch result {
case .success(let dictionary):
UserDefaults.standard.set(dictionary, forKey: "lastWeatherUpdate")
print(dictionary["latitude"])
case .failure(let error):
print(error.localizedDescription)
}
}
}