How can I extract jsonString from this method that depends on a task? - swift

Question

var temp = ""
let appid = "**************"
struct WeatherData {
// Object with latitude and longitude to process requests
// from OpenWeatherMap.
var lat, lon: Float
init(latitude: Float, longitude: Float) {
lat = latitude
lon = longitude
}
func retrieve() {
var jsonString = ""
// Send request to OpenWeatherMap.
let requestAddress = "https://api.openweathermap.org/data/2.5/weather?lat=\(lat)&lon=\(lon)&appid=\(appid)"
// Assign the URL to retrieve JSON, with ! dangerous
// operation.
let url = URL(string: requestAddress)!
let urlSession = URLSession(configuration: .ephemeral)
let task = urlSession.dataTask(with: url) {(data, response, error) in
let data = data
jsonString = String(data: data!, encoding: .utf8)!
print(jsonString)
}
task.resume()
}
}
var bangkok = WeatherData(latitude: 13.736717, longitude: 100.523186)
print(bangkok.retrieve())
print("Program running...")
print(temp)
RunLoop.main.run()
The issue I'm having is only print() works but not a return statement or an assignment to a global variable which is what I need. I ultimately want to parse this jsonString into a working dictionary except that I can't get it out of the function at the moment.
I'm depending on a webpage that has only text as body content.

Answer 1

It common to return the result via a completion block:
enum AppError : String, Error
{
case unknownFailure
case requestFailed
...
}
func retrieve(completion: #escaping (Result<Data, AppError>) -> Void)
{
...
let task = urlSession.dataTask(with: url)
{ (data, response, error) in
DispatchQueue.main.async
{
if let statusCode = (response as? HTTPURLResponse)?.statusCode,
statusCode != 200
{
completion(.failure(.requestFailed))
}
else if let data = data
{
completion(.success(data))
}
else if let error = error
{
completion(.failure(.requestFailed))
}
else
{
completion(.failure(.unknownFailure))
}
}
}
task.resume()
}
You need to choose where to convert the received Data to JSON and ultimately to some Codable struct.
You must also decide on how to handle errors and what detail you want to pass to a caller. In the above example I hide the details of dataTask() errors and put them all under app-custom .requestFailed.