Control when a different number of requests are completed in Swift - swift

Question

I have the following code that runs about :
for resFoto in resFotosResenhaEscolhidas {
jsonRequestUploadImagem = ResFotosModel.createJsonFotoResenha(resFoto)
let requestUploadImagem: NSMutableURLRequest = serviceRepository.clientURLRequest(wsUploadImagem, typeAutho: .basic, parms: "", body: jsonRequestUploadImagem as Dictionary<String, AnyObject>)
serviceRepository.post(requestUploadImagem, retryLogin: true, completion: {isOk,msgError,httpCode,needLogin,response in
self.checkResponseUploadImagemFotoResenha(response as AnyObject, httpCode)
})
}
func checkResponseUploadImagemFotoResenha(_ response:AnyObject, _ httpCode:Int) {
if httpCode != 200 {
let string = String(data: response as! Data, encoding: .utf8)
print( string!+" \n Erro HTTP: "+String(httpCode) )
} else {
// httpCode == 200
let data: Data = response as! Data // received from a network request, for example
let jsonResponse = try? JSONSerialization.jsonObject(with: data, options: [])
print("json response upload foto")
print(jsonResponse!)
}
}
The serviceRepository.post just run a "urlSession.dataTask", but I wanna know how can I control when the completion of the request.
The "resFotosResenhaEscolhidas" object contains 0 to 4 array inside it depending on the call. So, the code runs and create from 0 to 4 requests.
If the 4 requests are running, I just wanna know how can I check when they are finished?

Answer 1

Look at using a DispatchGroup. You'd create a DispatchGroup when you get ready to begin making network calls.
You'd call enter() on your dispatch group each time you begin a new URLSession task (or other async task.) You'd call leave() on the dispatch group in the completion handler for each task.
After you've submitted your async tasks, you'd call the dispatch group's notify() method to submit a block that will execute once all your async tasks are complete. (It's important that you wait until you've submitted your async tasks before calling notify(). If you try to call it before submitting your tasks, it invokes it's closure immediately since no tasks are running.)
I wrote a little demo project that uses a DispatchGroup to monitor a set of async tasks. (In the demo the tasks just delay for a random time before completing, and generate a random number.)
It waits until they've all completed, and then indicates the task that returned the largest value.
You can check it out on Github: DispatchGroupDemo on github