Alamofire number of requests one after another

Question

I have a number of requests witch I would like to call one after another without having nested spaghetti code.

I tried it already with a serial dispatch queue

let queue = dispatch_queue_create("label", DISPATCH_QUEUE_SERIAL)

Alamofire.request(Router.Countries).responseString { (response:Response<String, NSError>) in
            print(1)
        }

Alamofire.request(Router.Countries).responseString { (response:Response<String, NSError>) in
            print(2)
        }

Alamofire.request(Router.Countries).responseString { (response:Response<String, NSError>) in
            print(3)
        }

But unfortunately that does not work. The output of this can be 1,3,2 or 3,1,2 or any other combination.

What would be the best approach to get the output 1,2,3 so one after the other.

do you have n number of tries, or you already know how many request you will have? — Miknash, Jul 28 '16 at 08:32
I know how many Ill have but of course it would be better to be dynamic — Eike, Jul 28 '16 at 08:33
Have you tried to use a `dispatch_semaphore` ? I don't have time actually to reply with a good answer, but you can find a lot of examples here in SO — Luca D'Alberti, Jul 28 '16 at 08:53
Possible duplicate of [Chain multiple Alamofire requests](http://stackoverflow.com/questions/28634995/chain-multiple-alamofire-requests) — limfinity, Jul 28 '16 at 09:25

score 4 · Accepted Answer · answered Jul 28 '16 at 12:06

Ok I ended up writing my own implementation.

I created a class RequestChain wich takes Alamofire.Request as parameter

class RequestChain {
    typealias CompletionHandler = (success:Bool, errorResult:ErrorResult?) -> Void

    struct ErrorResult {
        let request:Request?
        let error:ErrorType?
    }

    private var requests:[Request] = []

    init(requests:[Request]) {
        self.requests = requests
    }

    func start(completionHandler:CompletionHandler) {
        if let request = requests.first {
            request.response(completionHandler: { (_, _, _, error) in
                if error != nil {
                    completionHandler(success: false, errorResult: ErrorResult(request: request, error: error))
                    return
                }
                self.requests.removeFirst()
                self.start(completionHandler)
            })
            request.resume()
        }else {
            completionHandler(success: true, errorResult: nil)
            return
        }

    }
}

And I use it like this

let r1 = Alamofire.request(Router.Countries).responseArray(keyPath: "endpoints") { (response: Response<[CountryModel],NSError>) in
    print("1")
}

let r2 = Alamofire.request(Router.Countries).responseArray(keyPath: "endpoints") { (response: Response<[CountryModel],NSError>) in
    print("2")
}

let r3 = Alamofire.request(Router.Countries).responseArray(keyPath: "endpoints") { (response: Response<[CountryModel],NSError>) in
    print("3")
}

let chain = RequestChain(requests: [r1,r2,r3])

chain.start { (success, errorResult) in
    if success {
        print("all have been success")
    }else {
        print("failed with error \(errorResult?.error) for request \(errorResult?.request)")
    }


}

Importent is that you are telling the Manager to not execute the request immediately

    let manager = Manager.sharedInstance
    manager.startRequestsImmediately = false

Hope it will help someone else

score 0 · Answer 2 · answered Jul 28 '16 at 10:26

0

I'm using Artman's Signals to notify my app once a result is returned, after which a queue elsewhere can call it's next request:

Alamofire.request( httpMethod, url, parameters: params ).responseJSON
{
    ( response: Response< AnyObject, NSError > ) in

    self._signals.dispatchSignalFor( Key: url, data: response.result )
}

More details here.

answered Jul 28 '16 at 10:26

Joseph Beuys' Mum

2,395
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50

Interesting approach! Thank for this hit but it will not fit in my code base. Thx – Eike Jul 28 '16 at 10:43

score -1 · Answer 3 · answered Jul 28 '16 at 08:51

One solution is to call your second request in the first one's callback :

Alamofire.request(Router.Countries).responseString { (response:Response<String, NSError>) in
            print(1)
            Alamofire.request(Router.Countries).responseString { (response:Response<String, NSError>) in
                 print(2)
                 Alamofire.request(Router.Countries).responseString { (response:Response<String, NSError>) in
                      print(3)
                 }
            }
        }

Alamofire number of requests one after another

3 Answers3