How to observe a published property via another observable 0bject - Swift Combine - swiftui

Question

[Edit]
I should point out that I am collecting data from a large number of sensors and having to pollute the view model, that is orchestrating this, with lots of #Published and subscriber code gets quite tedious and error prone.
I've also edited the code to be more representative of the actual problem.
[Original]
I'm trying to reduce the amount of code needed to observer a result from another class when using publishers. I would prefer to publish the result from a class that is generating the result instead of having to propagate it back to the calling class.
Here is a simple playground example showing the issue.
import SwiftUI
import Combine
class AnObservableObject: ObservableObject {
#Published var flag: Bool = false
private var timerPub: Publishers.Autoconnect<Timer.TimerPublisher>
private var timerSub: AnyCancellable?
init() {
timerPub = Timer.publish(every: 1, on: .current, in: .common)
.autoconnect()
}
func start() {
timerSub = timerPub.sink { [self] _ in
toggleFlag()
}
}
func stop() {
timerSub?.cancel()
}
func toggleFlag() {
flag.toggle()
}
}
class AnotherObservableObject: ObservableObject {
let ao = AnObservableObject()
func start() {
ao.start()
}
func stop() {
ao.stop()
}
}
struct MyView: View {
#StateObject var ao = AnotherObservableObject()
var body: some View {
VStack {
if ao.ao.flag {
Image(systemName: "flag").foregroundColor(.green)
}
HStack {
Button(action: {ao.start()}, label: {
Text("Toggle Flag")
})
Button(action: {ao.stop()}, label: {
Text("Stop")
})
}
}
.padding()
}
}
import PlaygroundSupport
PlaygroundPage.current.needsIndefiniteExecution = true
// Make a UIHostingController
let viewController = UIHostingController(rootView: MyView())
// Assign it to the playground's liveView
PlaygroundPage.current.liveView = viewController
let myView = MyView()
The Only way I have got this to work is to do this:
import SwiftUI
import Combine
class AnObservableObject: ObservableObject {
let flag = CurrentValueSubject<Bool, Never>(false)
private var subscriptions = Set<AnyCancellable>()
private var timerPub: Publishers.Autoconnect<Timer.TimerPublisher>
private var timerSub: AnyCancellable?
init() {
timerPub = Timer.publish(every: 1, on: .current, in: .common)
.autoconnect()
}
func start() {
timerSub = timerPub.sink { [self] _ in
toggleFlag()
}
}
func stop() {
timerSub?.cancel()
}
func flagPublisher() -> AnyPublisher<Bool, Never> {
return flag.eraseToAnyPublisher()
}
func toggleFlag() {
flag.value.toggle()
}
}
class AnotherObservableObject: ObservableObject {
let ao = AnObservableObject()
#Published var flag = false
init() {
let flagPublisher = ao.flagPublisher()
flagPublisher
.receive(on: DispatchQueue.main)
.assign(to: &$flag)
}
func start() {
ao.start()
}
func stop() {
ao.stop()
}
}
struct MyView: View {
#StateObject var ao = AnotherObservableObject()
var body: some View {
VStack {
if ao.flag {
Image(systemName: "flag").foregroundColor(.green)
}
HStack {
Button(action: {ao.start()}, label: {
Text("Toggle Flag")
})
Button(action: {ao.stop()}, label: {
Text("Stop")
})
}
}
.padding()
}
}
import PlaygroundSupport
PlaygroundPage.current.needsIndefiniteExecution = true
// Make a UIHostingController
let viewController = UIHostingController(rootView: MyView())
// Assign it to the playground's liveView
PlaygroundPage.current.liveView = viewController
let myView = MyView()
Thoughts?

Answer 1

You don't need an ObservableObject for this; you can observe a Timer directly in your View.
struct MyView: View {
#State private var flag: Bool = false
#State var timer = Timer.publish(every: 1, on: .main, in: .common).autoconnect()
var body: some View {
VStack {
if flag {
Image(systemName: "flag").foregroundColor(.green)
}
HStack {
Button(action: {start()}, label: {
Text("Toggle Flag")
})
Button(action: {stop()}, label: {
Text("Stop")
})
}
.onReceive(timer) { _ in
flag.toggle()
}
}
.padding()
}
func start() {
timer = Timer.publish(every: 1, on: .main, in: .common).autoconnect()
}
func stop() {
timer.upstream.connect().cancel()
}
}