Show error response in alert RxSwift using Driver - swift

Question

How to get an error response with driver so I can show it in alert. When I see the trait driver is can't error out, so should I use subject or behaviourRelay to get error response when I subscribe. Actually I like how to use driver but I don't know how to passed error response using driver.
this is my network service
func getMovies(page: Int) -> Observable<[MovieItem]> {
return Observable.create { observer -> Disposable in
self.service.request(endpoint: .discover(page: page)) { data, response, error in
if let _ = error {
observer.onError(MDBError.unableToComplete)
return
}
guard let response = response as? HTTPURLResponse, response.statusCode == 200 else {
observer.onError(MDBError.invalidResponse)
return
}
guard let data = data else {
observer.onError(MDBError.invalidData)
return
}
if let decode = self.decode(jsonData: MovieResults.self, from: data) {
observer.onNext(decode.results)
}
observer.onCompleted()
}
return Disposables.create()
}
}
This is my viewModel
protocol ViewModelType {
associatedtype Input
associatedtype Output
func transform(input: Input) -> Output
}
class PopularViewModel: ViewModelType {
struct Input {
let viewDidLoad: Driver<Void>
}
struct Output {
let loading: Driver<Bool>
let movies: Driver<[MovieItem]>
}
private let service: NetworkDataFetcher
init(service: NetworkDataFetcher = NetworkDataFetcher(service: NetworkService())) {
self.service = service
}
func transform(input: Input) -> Output {
let loading = ActivityIndicator()
let movies = input.viewDidLoad
.flatMap { _ in
self.service.getMovies(page: 1)
.trackActivity(loading)
.asDriver(onErrorJustReturn: [])
}
let errorResponse = movies
return Output(loading: loading.asDriver(),movies: movies)
}
}
this is how I bind the viewModel in viewController
let input = PopularViewModel.Input(viewDidLoad: rx.viewDidLoad.asDriver())
let output = viewModel.transform(input: input)
output.movies.drive { [weak self] movies in
guard let self = self else { return }
self.populars = movies
self.updateData(on: movies)
}.disposed(by: disposeBag)
output.loading
.drive(UIApplication.shared.rx.isNetworkActivityIndicatorVisible)
.disposed(by: disposeBag)

Answer 1

You do this the same way you handled the ActivityIndicator...
The ErrorRouter type below can be found here.
This is such a common pattern that I have created an API class that takes care of this automatically.
class PopularViewModel: ViewModelType {
struct Input {
let viewDidLoad: Driver<Void>
}
struct Output {
let loading: Driver<Bool>
let movies: Driver<[MovieItem]>
let displayAlertMessage: Driver<String>
}
private let service: NetworkDataFetcher
init(service: NetworkDataFetcher = NetworkDataFetcher(service: NetworkService())) {
self.service = service
}
func transform(input: Input) -> Output {
let loading = ActivityIndicator()
let errorRouter = ErrorRouter()
let movies = input.viewDidLoad
.flatMap { [service] in
service.getMovies(page: 1)
.trackActivity(loading)
.rerouteError(errorRouter)
.asDriver(onErrorRecover: { _ in fatalError() })
}
let displayAlertMessage = errorRouter.error
.map { $0.localizedDescription }
.asDriver(onErrorRecover: { _ in fatalError() })
return Output(
loading: loading.isActive.asDriver(onErrorRecover: { _ in fatalError() }),
movies: movies,
displayAlertMessage: displayAlertMessage
)
}
}