The state is saved as expected for these screens and the VM which works as expected, but because the VM isn’t cleared when it’s popped, I’m seeing flow collection that the VM is doing stick around after the fact.

So our VM collects a flow from a repository and every time I navigate to a different bottom bar destination and then back a new instance of the VM is created with the state restored from the previous instance, but the new instance has a new VM scope and starts a new collection of the repository flow.

this ends up leaking the collection jobs for this flow repeatedly and I’m not sure if I should be doing something else to avoid/detect this

We are getting a new instance of the VM when we come back to the destination after it has been popped off the backstack. But I can see in my logs that the old instances are still collecting the flow from the repo

So anytime the repo flow emits, the log indicating the flow is collected happens once for everytime the VM has been instantiated

I also added a log in the onCleared() override to confirm it is never called

You can check the

navBackStackEntry.id

to get the unique ID associated with each entry - that's the unique ID the VMs are associated with. If you aren't getting the same ID back, then these are new instances of the same destination, not a restored one

I’ll have to figure out why that is happening

My backstack is essentially going from

RootNavGraph > NavGraphA > Start-A

to

RootNavGraph > NavGraphB > Start-B

when switching between destinations in the bottom bar. So A and B are different items in the bottom bar. That navigation between items always looks like this:

navController.navigate(routeA) {
    launchSingleTop = true
    restoreState = true
    popUpTo(RootNavGraphName) {
         saveState = true
    }
}

The destination I’m looking at doesn’t have any nav arguments that would make the route different.

Behavior is the same when I do it that way except it pops up to the start destination of the root instead of the root itself which is fine, but it still is getting a new backstackEntry ID every time we come back to a bottom nav item.

So I debugged through what the nav controller is doing here and I think this might be an issue with how I’m using nested nav graphs. First I traced it to these lines in one of the navigate functions where it determines if it has state to restore and does the restore. My destination’s ID is never in that

backStackMap

// Starts at line 1695 in navigation 2.5.3
if (navOptions?.shouldRestoreState() == true && backStackMap.containsKey(node.id)) {
            navigated = restoreStateInternal(node.id, finalArgs, navOptions, navigatorExtras)
} else {
   // ...
}

Then I looked at where the state is saved in that map:

// Starts at line 585 in navigation 2.5.3, inside popBackStackInternal
if (savedState.isNotEmpty()) {
                val firstState = savedState.first()
                // Whether is is inclusive or not, we need to map the
                // saved state to the destination that was popped
                // as well as its parents (if it is the start destination)
                val firstStateDestination = findDestination(firstState.destinationId)
                generateSequence(firstStateDestination) { destination ->
                    if (destination.parent?.startDestinationId == destination.id) {
                        destination.parent
                    } else {
                        null
                    }
                }.takeWhile { destination ->
                    // Only add the state if it doesn't already exist
                    !backStackMap.containsKey(destination.id)
                }.forEach { destination ->
                    backStackMap[destination.id] = firstState.id
                }
                // And finally, store the actual state itself
                backStackStates[firstState.id] = savedState
            }

This section is called, but

savedState.first()

is always the intermediary nav graph for my destination rather than the screen destination itself. This is being set in

backStateMap

, but the other state in savedState which is for my destination that I try to navigate to does not appear to be used.

yeah, so we originally weren’t using nested nav graphs like this so these items were navigating to the destinations directly and we didn’t update that behavior when we added the nested nav graphs.

Thanks for the help!