RXSwift collectionView doesn't update when calling .onNext(newArray) - swift

Question

I got a problem. I got a collectionview which is binded to a winPinataActions PublishSubject<[Object]>(). Initially, when loading collectionview everything is fine, it displays as it has to the objects, however when the pull to refresh action changes the publishSubject data the UI is not updated, it still gets the old content of the PublishSubject.
Here is how I bind the collectionView :
class WinPinatasViewController: UIViewController {
#IBOutlet weak var collectionView: UICollectionView!
private let bag = DisposeBag()
override func viewDidLoad() {
super.viewDidLoad()
configureCollectionView()
}
func configureCollectionView() {
/..../
viewModel.winPinataActions
.observeOn(MainScheduler.instance)
.bind(to: collectionView.rx.items(cellIdentifier: "winPinatasCell", cellType: WinPinatasCell.self)) {(row, item, cell) in
cell.configureCell(with: item)
}.disposed(by: bag)
viewModel.getPinataActions()
}
#objc func handleRefreshControl() {
viewModel.getPinataActions()
DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
self.collectionView.refreshControl?.endRefreshing()
}
}
}
This is my viewModel class:
class WinPinatasViewModel {
let winPinataActions = PublishSubject<[WinPinatasAction]>()
func getPinataActions() {
guard let ssoId = UserDefaultsStore.ssoId() else {
return
}
NetworkEngine.shared.gamificationNetwork.getUserWinPinataActions(subject: winPinataActions, ssoID: ssoId)
}
}
And my NetworkEngine getuserPinataActions method:
func getUserWinPinataActions(subject winPinatasActions: PublishSubject<[WinPinatasAction]>, ssoID: String) {
//...//
let actions = try decoder.decode([WinPinatasAction].self, from: jsonData)
winPinatasActions.onNext(actions)
winPinatasActions.onCompleted()
//...//
}
When the pull to refresh action is done, the handleRefreshControl() method is called. Also While debugging I could see that after pullToRefresh action the new data is received inside my NetworkEngine method and both .onNext()and onCompleted() are called. But when I scroll through the collectionView the data the cell items are from the old array, not the one new one. Could you help me please? What am I doing wrong?

Answer 1

The problem here is that you are sending a completed event to the Subject but then expecting it to be able to send other events after that. The Observable contract specifies that once an Observable (or Subject in this case) sends a completed event, it will never send any more events under any circumstances.
Instead of passing a Subject into getUserWinPinataActions you should be returning an Observable from the function.
This is closer to what you should have:
class WinPinatasViewController: UIViewController {
#IBOutlet weak var collectionView: UICollectionView!
private let bag = DisposeBag()
let viewModel = WinPinatasViewModel()
override func viewDidLoad() {
super.viewDidLoad()
collectionView.refreshControl!.rx.controlEvent(.valueChanged)
.startWith(())
.flatMapLatest { [viewModel] in
viewModel.getPinataActions()
}
.observeOn(MainScheduler.instance)
.bind(to: collectionView.rx.items(cellIdentifier: "winPinatasCell", cellType: WinPinatasCell.self)) {(row, item, cell) in
cell.configureCell(with: item)
}
.disposed(by: bag)
}
}
class WinPinatasViewModel {
func getPinataActions() -> Observable<[WinPinatasAction]> {
guard let ssoId = UserDefaultsStore.ssoId() else {
return .empty()
}
return GamificationNetwork.shared.getUserWinPinataActions(ssoID: ssoId)
}
}
class GamificationNetwork {
static let shared = GamificationNetwork()
func getUserWinPinataActions(ssoID: String) -> Observable<[WinPinatasAction]> {
Observable.create { observer in
let jsonData = Data() // get jsonData somehow
let actions = try! decoder.decode([WinPinatasAction].self, from: jsonData)
observer.onNext(actions)
observer.onCompleted()
return Disposables.create { /* cancelation code, if any */ }
}
}
}
Remember:
Subjects provide a convenient way to poke around Rx, however they are not recommended for day to day use... In production code you may find that you rarely use the IObserver interface and subject types... The IObservable interface is the dominant type that you will be exposed to for representing a sequence of data in motion, and therefore will comprise the core concern for most of your work with Rx...
-- Intro to Rx
If you find yourself reaching for a Subject to solve a problem, you are probably doing something wrong.
Also, this article might help: Integrating RxSwift Into Your Brain and Code Base