Calling methods in swift (Method doesnt finish before next line) - ios

Question

Trying to pull in some JSON data from an API and then save that to core data.
My current method of doing this is to pull in the JSON data and return that array which ill then iterate and save to core data.
Pull in Data: (Works fine)
func getPlayerDataFromAPI() -> [Dictionary<String,AnyObject>]{
let url: String = "http://api.fantasy.nfl.com/v1/players/stats?"
let request : NSMutableURLRequest = NSMutableURLRequest()
var jsonData = [Dictionary<String,AnyObject>]()
request.HTTPMethod = "GET"
request.URL = NSURL(string: url)
session.dataTaskWithRequest(request) { (data, response, error) -> Void in
do {
let jsonResult = try NSJSONSerialization.JSONObjectWithData(data!, options:NSJSONReadingOptions.MutableContainers) as? NSDictionary
if (jsonResult != nil) {
if let playerData = jsonResult?["players"] as? [Dictionary<String, AnyObject>]{
jsonData = playerData
print(jsonData.count)
}
} else {
print("No Data")
}
}
catch {
print("Error Occured")
}
}.resume()
return jsonData;
}
And then I wanted to test the returned Dictionary to ensure it was being populated:
func saveData(){
let players = getPlayerDataFromAPI()
print(players.count)
}
I call saveData() in the viewController viewDidLoad method and get an empty dictionary... Moments later, the print statement in the JSON function prints.
0
1427
Is there a reason the getPlayerDataFromAPI() function doesnt finish before the print(count) is being called? Do I have this wrong logically? I always get an empty dictionary returned in this instance and thats no good.

Answer 1

You're trying to synchronously return the results of an asynchronous function. session.dataTaskWithRequest is passed a closure, which doesn't execute until the request completes. So your jsonData = playerData statement doesn't get executed until after your getPlayerDataFromAPI() function has already returned (at which point jsonData is still the empty dictionary you defined at the beginning of the function).
One way to do what you're trying to do is to allow a closure to be passed in to your function; something like this (I haven't tested this code):
func getPlayerDataFromAPI(completion: (data: [String: AnyObject]) -> Void)
Then, at the point you assign jsonData = playerData, you can "return" the data to the caller like this:
completion(data: jsonData)
Calling this function would look something like this:
getPlayerDataFromAPI() { (data) -> Void in
print(data)
}