Swift - append to array that is in an array - ios

Question

I am writing a class that returns JSON data. I create an array of the type NSArray. To this Array I add arrays of the type String.
I later want to append strings to the array of type String that is within the array of type NSArray.
However it does not allow this, I have no idea why because the append function does work when appending NSArrays to the main array.
This is the entire class:
import Foundation
class JSON {
struct Static {
let hostname = "http://192.168.2.115:8888/tcn/";
func getJSON(script:String, jsonMainElement:String, elements:[String]) -> [NSArray] {
var returnObject = [NSArray]()
let urlAsString = hostname + script;
let url = NSURL(string: urlAsString)!
let urlSession = NSURLSession.sharedSession()
let jsonQuery = urlSession.dataTaskWithURL(url, completionHandler: { data, response, error -> Void in
if (error != nil) {
println(error.localizedDescription);
}
var err: NSError?
var jsonResult = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableContainers, error: &err) as NSDictionary
if (err != nil) {
println("JSON Error \(err!.localizedDescription)");
}
var i = 0;
let arrayFromJson: [[String:String]] = jsonResult[jsonMainElement] as [[String:String]]
dispatch_async(dispatch_get_main_queue(), {
for item in arrayFromJson {
returnObject.append([String]());
for jsonObject in elements {
returnObject[i].append(item[jsonObject]!);
// ^ THIS LINE GIVES ERROR
}
i++;
}
if (arrayFromJson.count > 0) {
//k
}
})
})
jsonQuery.resume()
return returnObject;
}
}
}

Answer 1

You may need to define the array as containing a mutable array as below.
var returnObject = [NSMutableArray]()
You could also use a Swift 'sub' array, and define it more like this.
var returnObject = Array<Array<String>>()
Don't forget to update your return on the method.
func getJSON() -> Array<Array<String>>