Can't access data outside of closure in swift - swift

Question

I am trying to extract an array from closure in swift 3 and its not working for me. I have my JSON parser in the class WeatherGetter and I am calling it in the view did load file in the viewcontroller.swift how to assign the weather_data array to some outside variable?
class WeatherGetter {
func getWeather(_ zip: String, startdate: String, enddate: String, completion: #escaping (([[Double]]) -> Void)) {
// This is a pretty simple networking task, so the shared session will do.
let session = URLSession.shared
let string = "Insert API address"
let url = URL(string: string)
var weatherRequestURL = URLRequest(url:url! as URL)
weatherRequestURL.httpMethod = "GET"
// The data task retrieves the data.
let dataTask = session.dataTask(with: weatherRequestURL) {
(data, response, error) -> Void in
if let error = error {
// Case 1: Error
// We got some kind of error while trying to get data from the server.
print("Error:\n\(error)")
}
else {
// Case 2: Success
// We got a response from the server!
do {
var temps = [Double]()
var winds = [Double]()
let weather = try JSON(data: data!)
//print(weather)
let conditions1 = weather["data"]
let conditions2 = conditions1["weather"]
let count = conditions2.count
for i in 0...count-1 {
let conditions3 = conditions2[i]
let conditions4 = conditions3["hourly"]
let count2 = conditions4.count
for j in 0...count2-1 {
let conditions5 = conditions4[j]
let tempF = conditions5["tempF"].doubleValue
let windspeed = conditions5["windspeedKmph"].doubleValue
//temps.updateValue(tempF, forKey: "\(date)//\(j)")
temps.append(tempF)
winds.append(windspeed)
}
}
//print(temps)
//print(winds)
completion([temps, winds])
}
catch let jsonError as NSError {
// An error occurred while trying to convert the data into a Swift dictionary.
print("JSON error description: \(jsonError.description)")
}
}
}
// The data task is set up...launch it!
dataTask.resume()
}
}
override func viewDidLoad() {
super.viewDidLoad()
let weather = WeatherGetter()
weather.getWeather("13323", startdate: "2016-10-01", enddate: "2017-04-30"){(weather_data) -> Void in
print(weather_data[1])
}
//Do your stuff with isResponse variable.
}

Answer 1

You can assign it to a class property like this:
var weatherData: [[Double]]()
override func viewDidLoad() {
super.viewDidLoad()
let weather = WeatherGetter()
weather.getWeather("13323", startdate: "2016-10-01", enddate: "2017-04-30"){(weather_data) -> Void in
self.weatherData = weather_data
// reload or display data
}
}
You need to remember that the network request takes some time, so this is why you would call something like reloadData once you know you have received the response.
Say for example, the network response takes 100 milliseconds to respond. By the time the data has responded, all of the code in viewDidLoad will very likely be completely finished. So you need to respond to the data being received, when you receive it. If you have a bad mobile signal, it may take longer.
This is why you use callbacks/closures. They are called when the operation completes
UPDATE:
The code inside getWeather shows multiple errors for me and won't let me run it as is.
I managed to get a response from the weather API by modifying the code slightly and commenting alot out. Your main issue here is that you are not casting your JSON data to specific types.
// The data task retrieves the data.
let dataTask = session.dataTask(with: weatherRequestURL) {
(data, response, error) -> Void in
guard error == nil, let data = data else {
print("ERROR")
return
}
// Case 2: Success
// We got a response from the server!
do {
var temps = [Double]()
var winds = [Double]()
if let weather = try JSONSerialization.jsonObject(with: data, options: .allowFragments) as? [String:AnyObject] {
if let conditions1 = weather["data"] as? [String:AnyObject] {
print(conditions1)
}
}
} catch let jsonError {
// An error occurred while trying to convert the data into a Swift dictionary.
print("JSON error description: \(jsonError)")
}
}
dataTask.resume()
See in the code above how I am optionally unwrapping the values whilst casting their types. This is what you need to do throughout your code and check you get the right data at each step along the way. Unfortunately the API response is too large for me to do it here.
Unwrapping JSON Swift
Swift Closures
iOS Networking with Swift - This is a free course which I highly recommend. This is how I learnt iOS networking.

Answer 2

As mentioned by #Scriptable, it takes a while for the response to be processed since it's asynchronous. What you can do is to add the OperationQueue.main.addOperation to assign the current process to the main queue. This will prioritize the processing of your network response. You can also put your reloadData in this part.
var weatherData: [Double]()
override func viewDidLoad() {
super.viewDidLoad()
let weather = WeatherGetter()
OperationQueue.main.addOperation {
weather.getWeather("13323", startdate: "2016-10-01", enddate: "2017-04-30"){(weather_data) -> Void in
print(weather_data[1])
// reloadData()
}
}
}