Is it bad idea to create static stream in reactive programming? - ios

Question

Now I'm working on iOS using RxSwift framework. In my app I have to user user location, but I don't need it to be updated in real time. It's enough if location updated every time user opens app or does some defined action. Therefore, how about implementing singleton class where the last result is cached. Each update by action changes cached result and accepts it to the stream. Stream's default value is cached value. Then, views where user location is needed would subscribe on this stream.
Example implementation using Cache and RxSwift
import Foundation
import Cache
import CoreLocation
import RxSwift
import RxCocoa
class UserLocationManager: NSObject {
private enum Keys: String {
case diskConfig = "Disk Config"
case lastLocation = "User Last Location"
}
// MARK: - Variables
private func cache<T: Codable>(model: T.Type) -> Cache.Storage<T> {
let storage = try! Cache.Storage(diskConfig: DiskConfig(name: Keys.diskConfig.rawValue), memoryConfig: MemoryConfig(expiry: .never), transformer: TransformerFactory.forCodable(ofType: model))
return storage
}
private let locationManager = CLLocationManager()
private var lastPosition: MapLocation? {
get {
do {
return try cache(model: MapLocation.self).object(forKey: Keys.lastLocation.rawValue)
}
catch { return nil }
}
set {
do {
guard let location = newValue else { return }
try cache(model: MapLocation.self).setObject(location, forKey: Keys.lastLocation.rawValue)
}
catch { }
}
}
private let disposeBag = DisposeBag()
static let shared = UserLocationManager()
var locationStream = BehaviorRelay<CLLocationCoordinate2D?>(value: nil)
// MARK: - Methods
func updateLocation() {
if CLLocationManager.locationServicesEnabled() {
locationManager.requestLocation()
}
}
func subscribe() {
locationStream.accept(lastPosition?.clCoordinate2D)
locationStream.subscribe(onNext: { [weak self] location in
guard let `self` = self else { return }
guard let location = location else { return }
self.lastPosition = MapLocation(latitude: location.latitude, longitude: location.longitude)
}).disposed(by: disposeBag)
locationManager.delegate = self
}
// MARK: - Lifecycle
override init() {
super.init()
defer {
self.subscribe()
}
}
}
// MARK: - CLLocationManagerDelegate
extension UserLocationManager: CLLocationManagerDelegate {
func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
guard let location = locations.first else { return }
UserLocationManager.shared.locationStream.accept(location.coordinate)
}
func locationManager(_ manager: CLLocationManager, didFailWithError error: Error) {
}
}

Answer 1

There's no problem conceptually of having a global stream that can be subscribed to. However, your specific implementation is worrisome to me.
One of the cool things about Observable streams is that they are lazy, no work is done unless needed, but you are writing extra code to bypass that feature and I don't think it's necessary. Also, storing there current location when the app goes into the background and just assuming that is a valid location when the app comes back to the foreground (possibly weeks later) sounds inappropriate to me.
The RxCocoa package already has an Rx wrapper for CLLocationManager. It seems to me it would be far simpler to just use it. If you only need one location update then use .take(1). I'd be inclined to add a filter on the accuracy of the location before the take(1).