How can I synchronize closures? - ios

Question

How can I synchronize closures?
I have this code:
private func getWeather(parameters: [String : Any], failure: ((String) -> Void)? = nil ,completion: (() -> Void)? = nil) {
for _ in 0...10 {
RequestManager.sharedInstance.request(url: baseURL, parameters: parameters, completion: { (result) in
if JSON.parse(result)["name"].string == nil {
failure?("Something went wrong. Please, try again later")
} else {
let weatherModel: WeatherModel = WeatherModel(json: JSON.parse(result))
}
})
}
completion?()
}
In my code, completion?() will call, not when all requests will ended
And I need call completion?() when all requests will ended. Ho can I do it?

Answer 1

Since the currently accepted answer isn't correct, here is a version that properly uses a DispatchGroup.
private func getWeather(parameters: [String : Any], failure: ((String) -> Void)? = nil ,completion: (() -> Void)? = nil) {
let dispatchGroup = DispatchGroup()
for _ in 0...10 {
dispatchGroup.enter()
RequestManager.sharedInstance.request(url: baseURL, parameters: parameters) { result in
if JSON.parse(result)["name"].string == nil {
failure?("Something went wrong. Please, try again later")
} else {
let weatherModel: WeatherModel = WeatherModel(json: JSON.parse(result))
}
dispatchGroup.leave()
}
}
dispatchGroup.notify(queue: DispatchQueue.main) {
completion?()
}
}

Answer 2

An easy way to do this is just to count completed calls.
private func getWeather(parameters: [String : Any], failure: ((String) -> Void)? = nil ,completion: (() -> Void)? = nil) {
let numCalls = 11;
var completedCalls = 0;
for _ in 0..<numCalls {
RequestManager.sharedInstance.request(url: baseURL, parameters: parameters, completion: { (result) in
if JSON.parse(result)["name"].string == nil {
failure?("Something went wrong. Please, try again later")
} else {
let weatherModel: WeatherModel = WeatherModel(json: JSON.parse(result))
}
completedCalls += 1
if completedCalls == numCalls {
completion?()
}
})
}
}
Your completion callback runs when each request ends. Making each of your completion callbacks update a value in its enclosing scope allows you to keep track of how many requests have ended. When all the requests you expect have ended, you call completion?().