Asynchronous Request (Order Matters) - asynchronous

Question

I'm using Alamofire to execute a number of asynchronous requests concurrently, and SwiftyJSON to handle the response.
I need help making sure that appending to moviesByCategory occurs in order.
For example, the "top_rated" data response should be the first element appended to moviesByCategory, not "upcoming".
var moviesByCategory = [[JSON]]()
override func viewDidLoad() {
super.viewDidLoad()
let apiEndPoints = ["top_rated", "popular", "now_playing", "upcoming"]
let dispatchGroup = DispatchGroup()
for endPoint in apiEndPoints {
let endPointURL = URL(string: "https://api.themoviedb.org/3/movie/\(endPoint)?api_key=\(apiKey)&language=en-US&page=1")!
dispatchGroup.enter()
getMoviesFromEndPoint(url: endPointURL)
}
dispatchGroup.notify(queue: DispatchQueue.main) {
self.tableView.reloadData()
}
}
func getMoviesFromEndPoint(url: URL, group: dispatchGroup) {
Alamofire.request(url).responseData { response in
if let data = response.result.value {
let json = JSON(data: data)
self.moviesByCategory.append(json["results"].arrayValue)
}
}
}
The purpose for DispatchGroup is to reload the UITableView once all requests have completed.
Any help with this would be tremendously appreciated. Please do point out where I am wrong.

Answer 1

Add a completion handler parameter to getMoviesFromEndPoint:
func getMoviesFromEndPoint(url: URL, completion: () -> Void) { ... }
and leave the group within after the network call completed:
getMoviesFromEndPoint(url: endPointURL) {
dispatchGroup.leave()
}
Complete code:
override func viewDidLoad() {
super.viewDidLoad()
let apiEndPoints = ["top_rated", "popular", "now_playing", "upcoming"]
let dispatchGroup = DispatchGroup()
for endPoint in apiEndPoints {
let endPointURL = URL(string: "https://api.themoviedb.org/3/movie/\(endPoint)?api_key=\(apiKey)&language=en-US&page=1")!
dispatchGroup.enter()
getMoviesFromEndPoint(url: endPointURL) {
dispatchGroup.leave()
}
}
dispatchGroup.notify(queue: DispatchQueue.main) {
self.tableView.reloadData()
}
}
func getMoviesFromEndPoint(url: URL, completion: () -> Void) {
Alamofire.request(url).responseData { response in
if let data = response.result.value {
let json = JSON(data: data)
self.moviesByCategory.append(json["results"].arrayValue)
}
completion()
}
}