ObservableObject and Condition - timer

Question

I have a code for a timer that starts automatically and should stop again with an if statement. Unfortunately, that doesn't work and I don't get an error message. what am I doing wrong here?
import SwiftUI
import Combine
import Foundation
class WaitingTimerClass: ObservableObject {
#Published var waitingTimerCount: Int = 0
var waitingTimer = Timer()
func start() {
self.waitingTimer = Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { timer in self.waitingTimerCount += 1 } }
func stop() { waitingTimer.invalidate() }
func reset() { waitingTimerCount = 0; waitingTimer.invalidate() }
}
struct ContentView: View {
#ObservedObject var observed = WaitingTimerClass()
var body: some View {
Text("\(self.observed.waitingTimerCount)")
.onAppear {
self.observed.start()
if self.observed.waitingTimerCount == 3 {
self.observed.stop()
}
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
``

Answer 1

The code in onAppear block works only once, when the View appears (or several times, when view disappear and appear again). In your case waitingTimerCount will always be 0. If you need to observe some value from the view use onReceive. The code should looks like this:
struct TimerWaiter: View {
#ObservedObject var observed = WaitingTimerClass()
var body: some View {
Text("\(self.observed.waitingTimerCount)")
.onAppear {
self.observed.start()
}
.onReceive(observed.$waitingTimerCount) { count in
guard count == 3 else { return }
self.observed.stop()
}
}
}
update for first author's comment: I can't figure out, why reseting timer is not working as expected and I have not much time today. Maybe tomorrow it will be easier to understand. Here is not quite good, but worked solution:
class WaitingTimerClass: ObservableObject {
#Published var waitingTimerCount: Int = 0
var didInvalidate = PassthroughSubject<Void, Never>()
var waitingTimer = Timer()
func start() {
self.waitingTimer = Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { timer in self.waitingTimerCount += 1 } }
func stop() { waitingTimer.invalidate() }
func reset() {
waitingTimer.invalidate()
waitingTimerCount = 0
didInvalidate.send()
}
}
struct TimerWaiter: View {
#ObservedObject var observed = WaitingTimerClass()
#State private var count = 0
var body: some View {
Text("\(count)")
.onAppear {
self.observed.start()
}
.onReceive(observed.$waitingTimerCount) { count in
self.count = count
guard count == 3 else { return }
self.observed.reset()
}
.onReceive(observed.didInvalidate) { _ in
self.count = 0
}
}
}
P.S. I will try to dig deeper to understand, why the last changing of waitingTimerCount does not affect View

Answer 2

.onAppear {
self.observed.start()
if self.observed.waitingTimerCount == 3 {
self.observed.stop()
}
}
How this code works?
it is running when the View Appears (most likely only once)
start the timer
checked if waitinigTimer == 3 // it is not 3 at this moment
return
So, it simply never stop, as you already know.
If you like to stop it if waitingTimer == 3, you have to do it in your model.
#Published var waitingTimerCount: Int = 0 {
willSet {
if newValue == 3 { stop() }
}
}

Answer 3

Thank you very much. the solution to the reset problem can be found here:
ObservableObject bug or not