How to use JSON Results created in a function [duplicate] - ios

Question

This question already has answers here:
Returning data from async call in Swift function
(13 answers)
Closed 6 years ago.
I'm parsing JSON data from a remote service. i wrote a function wich do the parsing process. This function has a return value. The result is created in this function and saved in a global property. But when i call the function in viewDidLoad i get an empty result:
Here is my code
class ViewController: UIViewController {
var rates = [String:AnyObject]()
override func viewDidLoad() {
super.viewDidLoad()
print(getRates("USD")) // <- Gives me an empty Dictionary
}
func getRates(base: String) -> [String:AnyObject]{
let url = NSURL(string: "http://api.fixer.io/latest?base=\(base)")!
let urlSession = NSURLSession.sharedSession()
let task = urlSession.dataTaskWithURL(url) { (data, response, error) in
do{
self.rates = try NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions()) as! [String:AnyObject]
//print(self.rates) //<-- Gives me the right output, but i want to use it outside.
}
catch{
print("Something went wrong")
}
}
task.resume()
return self.rates //<- returns an empty Dictionary
}
I can only get the right result inside the function, but I can't use it outside. What is wrong here?
EDIT:
Tank you! All answers are working, but is there a way to store the result in a global property so that i can use the result anywhere? Assuming i have a tableView. Then i need to have the result in a global property

Answer 1

You cannot return response value at once - you have to wait until response arrives from network. So you have to add a callback function (a block or lambda) to execute once response arrived.
class ViewController: UIViewController {
var rates = [String:AnyObject]()
override func viewDidLoad() {
super.viewDidLoad()
getRates("USD"){(result) in
print(result)
}
}
func getRates(base: String, callback:(result:[String:AnyObject])->()){
let url = NSURL(string: "http://api.fixer.io/latest?base=\(base)")!
let urlSession = NSURLSession.sharedSession()
let task = urlSession.dataTaskWithURL(url) { (data, response, error) in
do{
self.rates = try NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions()) as! [String:AnyObject]
callback(self.rates)
//print(self.rates) //<-- Gives me the right output, but i want to use it outside.
}
catch{
print("Something went wrong")
}
}
task.resume()
}

Answer 2

Because you are using NSURLSession and the task is asynchronous you will need to use a completion handler. Here is an example:
//.. UIViewController Code
var rates = [String: AnyObject]()
override func viewDidLoad() {
super.viewDidLoad()
getRates("USD") { [weak self] result in
self?.rates = result
}
}
func getRates(base: String, completion: [String: AnyObject] -> Void) {
let url = NSURL(string: "http://api.fixer.io/latest?base=\(base)")!
let urlSession = NSURLSession.sharedSession()
let task = urlSession.dataTaskWithURL(url) { (data, response, error) in
do {
let rates = try NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions()) as! [String:AnyObject]
completion(rates)
}
catch {
print("Something went wrong")
}
}
task.resume()
}

Answer 3

Try this on your code:
class ViewController: UIViewController {
var rates = [String:AnyObject]()
override func viewDidLoad() {
super.viewDidLoad()
getRates() { (result) in
print(result)
}
}
func getRates(completion: (result: Array)) -> Void{
let url = NSURL(string: "http://api.fixer.io/latest?base=\(base)")!
let urlSession = NSURLSession.sharedSession()
let task = urlSession.dataTaskWithURL(url) { (data, response, error) in
do{
self.rates = try NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions()) as! [String:AnyObject]
completion(self.rates)
}
catch{
print("Something went wrong")
}
}
task.resume()
return self.rates //<- returns an empty Dictionary
}
}