Correct way to collect a SingleShotEventBus used for navigation events?

[marcardar]

I use a SingleShotEventBus to communicate navigation events to a Composable which, in turn, will push the appropriate screens using the navigator.

In the Composable, I collect these events this way:

LaunchedEffect(Unit) {
    viewModel.navigationEvents.launchAndRepeatedlyCollect(activity) { navigationEvent ->
        ...
    }
}

However, while this works initially, after screen rotation, it doesn't (nothing is collected).

How to write this properly?

[marcardar]

It's probably a good idea to describe how I'm using Voyager (in Android) here.

In the main Activity I have an XML layout that declares a ComposeView and initialise it with:

containerComposeView.setContent {
    Navigator(ContainerScreen())
}

and then:

class ContainerScreen: Screen {
    @Composable
    override fun Content() {
        val activity = LocalContext.current.toActivityOrThrow() as ComponentActivity
        val navigator = LocalNavigator.currentOrThrow
        LaunchedEffect(Unit) {
             viewModel.navigationEvents.launchAndRepeatedlyCollect(activity) { navigationEvent ->
                 when (navigationEvent) {
                     NavigationEvent.Foo -> {
                         navigator.push(FooScreen())
                     }
                     ...
                 }
        ...

Think of the ContainerScreen as a placeholder (a pane in the main screen) to hold screens triggered by the navigation events.

Perhaps this is the problem? The ContainerScreen is not at the top of the stack and so is disposed?

[marcardar]

It seems the problem is that when the device is rotated, the ContainerScreen is disposed and so the flow collection is stopped. Because the ContainerScreen is not visible (it's behind whatever secondary screen it navigated to), it is not instantiated until the user backs out of the secondary screen.

So that explains what is happening. But this begs the question, where are you supposed to collect such navigation events?

Or, is there a way to recreate the backstack of screens? Because it makes more sense that following device rotation the stack should be the same as before device rotation.

[marcardar]

I seem to have found a solution by changing the ContainerScreen to have empty content and declare the LaunchedEffect in the Navigator's content arg instead:

Navigator(
    screen = ContainerScreen(),
    content = { navigator ->
        LaunchedEffect(Unit) {
            viewModel.navigationEvents.launchAndRepeatedlyCollect(activity) { navigationEvent ->
                ...
            }
        }
        CurrentScreen()
    }
)

class ContainerScreen: Screen {
    @Composable
    override fun Content() {
        // no content needed
    }
}

Have I stumbled upon the correct way to do this?