JSON parsing and returning data in Swift - ios

Question

i have a Swift code for retrieving and parsing JSON data from the web. everything seems to work fine except one problem i am facing right now. I tried to solve it for some time, have check all sources online.
I have created global dictionary "dicOfNeighbours" that would like to return as a result of parse to other class by calling "func startConnection".
dicOfNeighbours stores parsed data till it goes out of the closing bracket of the:
"let task = session.dataTaskWithRequest(urlRequest) { ... }"
After it stores just nil. And returned result is nil as well.
I have tried to pass "dicOfNeighbours" variable by reference using inout and it is still returns nil result.
there might some solution that i missed.
I would appreciate any help and suggestions.
Thanks!
var dicOfNeighbours = Dictionary<String, [Int]>()
func startConnection() -> Dictionary<String, [Int]>{
let requestURL: NSURL = NSURL(string: "http://www....data.json")!
let urlRequest: NSMutableURLRequest = NSMutableURLRequest(URL: requestURL)
let session = NSURLSession.sharedSession()
let task = session.dataTaskWithRequest(urlRequest) {
(data, response, error) -> Void in
let httpResponse = response as! NSHTTPURLResponse
let statusCode = httpResponse.statusCode
if (statusCode == 200) {
do{
let json = try NSJSONSerialization.JSONObjectWithData(data!, options:.AllowFragments)
if let neighbours = json["neighbours"] as? [String: Array<Int>] {
var i = 0
for (index, value) in neighbours {
self.dicOfNeighbours[index] = value
}
}
}catch {
print("Error with Json: \(error)")
}
}
}
task.resume()
return self.dicOfNeighbours
}

Answer 1

You are using return instead of using a callback. You are doing your parsing when the network connection is done; asynchronously.
To synchronize it, you'd need to use semaphores, but that is highly discouraged on the main thread.
Instead, do the appropriate things with the result when your completion block is executed. Think of the data task as 'do stuff, come back to me when you're done'.