singleton viewmodel becoming unable to launch coroutine after popBackStack

[mannyvw]

Describe the bug
Happy to be told its something im doing wrong but this seems very strange to me took me a while to track down the cause but basically ViewModels getting corrupted ? on use on popBackStack or swipe left when created vm singletons using singleOf(::NameViewModel), leaving the viewmodel not able to launch coroutines. Am guessing its just because detailscreen goes out of scope with VM attached to it, but as its a singleton it should still be available elsewhere ?

To Reproduce
Steps to reproduce the behavior:

1. Create vm using singleOf(::NameViewModel)
2. Add two screens that navigate from one to other
3. reference vm in 2nd screen and 1st (should be same vm)
4. use swipe left on android to navigate back to root screen (or can use popBackStack on a button)

Expected behavior
vm is still available to launch coroutines in vm. Coroutine just don't start

`
class MyViewModel : ViewModel() {
var name = "Hello"
private var _coroutineRunCount = MutableStateFlow(0)
var coroutineRunCount : StateFlow = _coroutineRunCount

fun runCoroutine() {
    println("runCoroutine")
    viewModelScope.launch {
        println("runCoroutine - Launched *****")
        _coroutineRunCount.value += 1
    }
}

}
**Koin module and version:** [e.g]:koin-core:4.1.1`

Snippet or Sample project to help reproduce
WeirdIssueApp 3.zip

[arnaudgiuliani]

Hello,

Your ViewModel shouldn't be declared as single but viewModel instead. You should share your ViewModel from navigation backstack or activity.

[ocetin00]

Firstly, you should use viewModelOf(::MyViewModel) instead of singleOf. When you create a singleton, you pass the same object to the screens, and one of them cancels the viewModelScope.

vm is still available to launch coroutines in vm. Coroutine just don't start

This is because when you go back to the first screen from the second one, the second screen is popped from the back stack and onCleared() is triggered. This cancels the viewModelScope, and you cannot launch coroutines in a scope that has already been cancelled.