RxSwift & alamofire, How to send http request after previous request arrived? - alamofire

Question

I need to send http request in RxSwift & Alamofire circumstance and send it synchronously which means ...
send(1)...response(1)
-------------------- send(2)...response(2)
-----------------------------------------send(3)...response (3)
and This is my code
Observable.from(devicesArray)
.concatMap { (device) in
return HTTPRequest.deleteDevice(withDevice: device)
}.subscribe({ (event) in
log.debug("Remove device successfully")
}).disposed(by: self.disposeBag)
and deleteDevice is
func deleteDevice(withDevice device:Device) -> Single<String> {
return Alamofire.request("http://example.com/\(device.deviceId)", method: .delete, parameters: nil, headers: self.headers()).rx
.responseJSON()
.retry(self.retryMaxAttempCount)
.asSingle()
.observeOn(SerialDispatchQueueScheduler(qos: .default))
.map({ (response) in
guard let json = response.value as? [String: Any] else {
throw HTTPManagerError.invalidResponse
}
guard let resultCode = json["resultCode"] as? String else {
throw HTTPManagerError.invalidResponse
}
if resultCode == "0000" || resultCode == "0101" {
return resultCode
} else {
throw HTTPManagerError.invalidResponse
}
})
.observeOn(MainScheduler.instance)
}
Now every single HTTPRequest.deleteDevice function requested in parallel.
So How could I make this request wait until a previous request get finished?
Thanks.

Answer 1

The key here is to make an array of observables and concat them:
// first we create a deleteDevice observable for each item.
// Remember, they don't actually make a network call until subscribed to and concat only subscribes to each once the previous one is done.
Observable.concat(
devicesArray.map { deleteDevice(withDevice: $0) }
.map { $0.asObservable() } // because concat doesn't exist for Singles.
.map { $0.catchErrorJustReturn("\($0) not deleted.") } // make sure that all deletes will be attempted even if one errors out.
)
// the above will emit a string every time a delete finishes.
// `.toArray()` will gather them together into an array.
.toArray()
.subscribe(onNext: { results in
})
.disposed(by: disposeBag)