RxSwift - Receive the same event at two ViewControllers at the same time - ios

Question

Hi i'm just getting started with RxSwift and decided to make simple Currency Exchange application. My app has two view's (allCurrenciesList and userFavouritesView). Basically all logic works, but only if i run networking func every single time one of view didAppear/didLoad. My point is two fetch it only once, and received many times, when necessary. Application fetch dictionary of currencies and in ViewModel pass it to BehaviorSubject, and when view being load/appear it just subscribe it, and use it in UITableView. Thanks
class ListViewModel {
let service: CurrencyService!
var curriencies = BehaviorRelay<[Currency]>(value: [])
var currienciesObservable: Observable<[Currency]> {
return curriencies.asObservable().share()
}
let disposeBag = DisposeBag()
init(service: CurrencyService) {
self.service = service
}
func fetchAllCurrencies() {
self.service.fetchAllSymbols { result in
switch result{
case .success(let currencies):
self.dictionaryIntoArray(currencies: currencies["symbols"] as! [String : Any])
case .failure:
print("error")
}
}
}
private func dictionaryIntoArray(currencies: [String: Any]) {
var currencyArray = [Currency]()
for (symbol, name) in currencies {
currencyArray.append(Currency(symbol: symbol, fullName: name as! String))
}
let sortedArray = currencyArray.sorted { $0.fullName < $1.fullName }
self.curriencies.accept(sortedArray)
}
allCurrenciesList
override func viewDidLoad() {
super.viewDidLoad()
setupView()
configureTableViewDataSource()
tableView.delegate = self
fetchData()
}
private func fetchData() {
viewModel.fetchAllCurrencies() // this func is necceserry everysingle time
viewModel.currienciesObservable.subscribe(onNext: { curriencies in
self.applySnapshot(curriencies: curriencies)
}).disposed(by: disposeBag)
}
userFavouritesView
override func viewDidLoad() {
super.viewDidLoad()
viewModel.fetchAllCurrencies() // this func is necceserry everysingle time
viewModel.currienciesObservable.subscribe(onNext: { allCurencies in
let selectedItems = UserDefaults.standard.array(forKey: "SelectedCells") as? [Int] ?? [Int]()
var currenciesArray: [Currency] = []
selectedItems.forEach { int in
self.pickerValues.append(allCurencies[int])
currenciesArray.append(allCurencies[int])
}
self.applySnapshot(curriencies: currenciesArray)
}).disposed(by: disposeBag)
}

Answer 1

The key here is to not use a Subject. They aren't recommended for regular use. Just define the currienciesObservable directly.
Something like this:
class ListViewModel {
let currienciesObservable: Observable<[Currency]>
init(service: CurrencyService) {
self.currienciesObservable = service.rx_fetchAllSymbols()
.map { currencies in
currencies["symbols"]?.map { Currency(symbol: $0.key, fullName: $0.value as! String) }
.sorted(by: { $0.fullName < $1.fullName }) ?? []
}
}
}
extension CurrencyService {
func rx_fetchAllSymbols() -> Observable<[String: [String: Any]]> {
Observable.create { observer in
self.fetchAllSymbols { result in
switch result {
case let .success(currencies):
observer.onNext(currencies)
observer.onCompleted()
case let .failure(error):
observer.onError(error)
}
}
return Disposables.create()
}
}
}
With the above, every time you subscribe to the currenciesObservable the fetch will be called.

Answer 2

As I understand, it's because your fetchAllSymbols function was not stored in the DisposeBag.
func fetchAllCurrencies() {
self.service.fetchAllSymbols { result in
switch result{
case .success(let currencies):
self.dictionaryIntoArray(currencies: currencies["symbols"] as! [String : Any])
case .failure:
print("error")
}
}.dispose(by: disposeBag)
}