Replay last request with RxSwift - swift

Question

I'm creating a networking layer where I inject API provider and call event to the initialize method.
class NetworkingLayer<T: Decodable, E: TargetType> {
var response: Driver<T>
init(provider: MoyaProvider<E>, request: Singal<E>) {
let requestState = request
.flatMapLatest({
provider.rx.request($0).map(Respose<T>.self)
.map { ReqestState.loaded($0) }
.asDriver(onErrorRecover: { error in
return Driver.just(.error(error))
})
.startWith(.loading)
})
.asDriver(onErrorRecover: { fatalError($0.localizedDescription) })
response = requestState
.map({ $0.data?.data })
.filterNil()
}
}
Using them in the following way:
class ViewModel {
let networking: DataNetworkingResponse<[TagItem], ScoutEnpoint>
init(provider: MoyaProvider<Endpoint>, event: Singal<[Int]>) {
let request = event
.map({ Endpoint.getNewItems(prevItemsIds: $0) })
self.networking = NetworkingLayer(provider: provider, request: request)
}
}
All working like charm. But now I have to implement refresh feature. Refresh my last request. I've added this let refresh: Signal<()> = Signal.empty() property to my network layer. But can't understand how to save my last request.
class NetworkingLayer<T: Decodable, E: TargetType> {
let refresh: BehaviorRelay<()> = BehaviorRelay.init(value: ())
...
}
How can I implement refreshing like this?
viewModel.networking.refresh.accept(())

Answer 1

Using a BehaviorRelay is a bad idea because it emits a value as soon as it's subscribed to. This means that your NetworkingLayer object would make a request as soon as it's constructed.
Better would be to pass another Signal into the init method:
init(provider: MoyaProvider<E>, request: Singal<E>, refresh: Signal<Void>)
I don't know Moya but here's how I would have written something like that using URLSession:
enum RequestState<T> {
case loaded(T)
case error(Error)
case loading
}
class NetworkingLayer<T: Decodable> {
let response: Driver<RequestState<T>>
init(request: Signal<URLRequest>, refresh: Signal<Void>, provider: URLSession = URLSession.shared, decoder: JSONDecoder = JSONDecoder()) {
response = Observable.merge(request.asObservable(), refresh.withLatestFrom(request).asObservable())
.flatMapLatest { request in
provider.rx.data(request: request)
.map { try decoder.decode(T.self, from: $0) }
.map { RequestState.loaded($0) }
.startWith(.loading)
.catchError { Observable<RequestState<T>>.just(.error($0)) }
}
.share(replay: 1)
.asDriver(onErrorRecover: { fatalError($0.localizedDescription) })
}
}
I threw the share(replay:) on there so that subsequent subscribers won't make separate network requests, and I made the decoder injectable so the caller can configure it how they want.