Delay task until completed - ios

Question

It is a very common question for people to ask "How do I delay a function or a chunk of code?" but that is not what I need here.
I need my code to wait until a certain task is complete, otherwise my function receives an error that I have no access_token (as the code doesn't wait for fetching the data from the Spotify server).
Here is my code so far, with the attempt to add a DispatchGroup:
func getAccessToken() throws -> Spotify.JSONStandard {
var accessToken: Spotify.JSONStandard!
let group = DispatchGroup() // <- Create group
group.enter() // <- Enter group
Alamofire.request("https://accounts.spotify.com/api/token", method: .post, parameters: spotify.parameters, headers: nil).responseJSON(completionHandler: {
response in
// Check if response is valid
if let newValue = response.result.value as? Spotify.JSONStandard {
accessToken = newValue
}
group.leave() // <- Leave group
})
group.wait() // <- Wait until task is completed
// \/ Delay this code until complete \/
if accessToken != nil {
return accessToken
}
else {
throw SpotifyError.failedToGetAccessToken
}
// /\ /\
}
Without the groups, my code throws SpotifyError.failedToGetAccessToken (the access_token is nil).
However, after adding the groups, my code just hangs and waits forever. How can I delay this code from being completed?
I know getting the token has no issues, as if I remove the return and place a print within the request, I get my expected result.
If you have any questions, please ask

Answer 1

Don't try to make an asynchronous task synchronous
This is a solution with a completion handler and a custom enum for convenience
enum Result {
case success(Spotify.JSONStandard), failure(Error)
}
func getAccessToken(completion: #escaping (Result)->()) {
Alamofire.request("https://accounts.spotify.com/api/token", method: .post, parameters: spotify.parameters, headers: nil).responseJSON(completionHandler: {
response in
// Check if response is valid
if let newValue = response.result.value as? Spotify.JSONStandard {
completion(.success(newValue)
} else {
completion(.failure(SpotifyError.failedToGetAccessToken))
}
})
}
and call it
getAccessToken { result in
switch result {
case .success(let token) : // do something with the token
case .failure(let error) : // do something with the error
}
}