You must make two HTTP network requests at the same time (with a completion handler after both are completed)

Question

I have a situation where I need to make two HTTP GET requests and process their results only after they are completed. I have a completion handler for each individual network request, but this does not help, since I do not know when the data is extracted from both requests.

I have limited experience with GCD, but now that Swift 3 is out, I'm trying to figure out how to complete several tasks and have one completion handler for them. My research has shown that a GCD or NSOperationQueue solution may be the solution I'm looking for. Can anyone help suggest what tool is suitable for working and what the code looks like in Swift 3?

Answer 1

You must use the send groups included in the group before issuing the request and leaving the group in the completion handler for the request. So, suppose for a second you had some method that performed an asynchronous request, but provided a completion handler parameter, which was a closure that would be called when the network request was executed:

func perform(request: URLRequest, completionHandler: @escaping () -> Void) { ... }

To run these two simultaneous requests and get notified when they are done, you will do something like:

let group = DispatchGroup()

group.enter()
perform(request: first) {
    group.leave()
}

group.enter()
perform(request: second) {
    group.leave()
}

group.notify(queue: .main) {
    print("both done")
}

, perform(request:) (, ), , , URLSession Alamofire. GCD, .

Answer 2

: dispatch_after GCD Swift 3? dispatch_group . ( ObjC):

dispatch_group_t group = dispatch_group_create();

//startOperation1
dispatch_group_enter(group);

//finishOpeartion1
dispatch_group_leave(group);


//startOperation2
dispatch_group_enter(group);

//finishOpeartion2
dispatch_group_leave(group);


//Handle both operations completion
dispatch_group_notify(group, dispatch_get_main_queue(), ^{ 
//code here
});