question for those who are using one `NavHost`, on...

# compose

[james]

question for those who are using one NavHost, one Scaffold and BottomNavigation at the root level, with many nested screens & Composables under that: is there a recommended way to show and hide the BottomNavigation?

I have a nested LazyColumn which I’d like to use to trigger showing/hiding of that BottomNavigation when I scroll up/down. this is fairly simple when the BottomNavigation is “closer” to the Composable triggering it, but when it’s deeply nested I wonder what the best solution is?

do I simply pass a lambda like toggleBottomNavigationVisibility all the way from the top level where the Scaffold is, through many Composables, down into my deeply nested one? this would work but I would like to know if there’s a better way and my brain isn’t seeing it 😄

[Alex Vanyo]

https://issuetracker.google.com/issues/217465473#comment6 has some discussion around a similar problem. That one is specifically for a PostionIndicator for Compose for Wear, but the same principle applies, since you’re trying to have a top-level component (in this case, a BottomNavigation) be driven by state that is scoped to a specific destination (a LazyColumn at some nested route)

The issue has the full details, but the summary is setting up a shared ViewModel. You can use get access to that ViewModel in two places: Outside the NavHost to drive the BottomNavigation visibility, and inside the NavHost for the specific destination.

[james]

great, that’s the exact kind of advice I was looking for, thanks Alex

[Colton Idle]

Don't the docs for this talk about how this should be done via routes?

[james]

😮 really? Got a link @Colton Idle? Curious to see how that would work

[Colton Idle]

https://developer.android.com/jetpack/compose/navigation#bottom-nav

[Colton Idle]

ah

[Colton Idle]

sorrry. i see your point though. you want the lazy col to trigger when its going up and down. sorry.

[james]

oh yep, the docs example of routes usage is how the rest of my nav architecture is built, it was just the triggering of showing/hiding the bottom nav bar that I was curious about.. and even then, there's a few ways to do it that all work, but I was curious about the "right" way, since I believe some of my ideas were absolutely not right 😂

[Alex Vanyo]

Right, you don’t have to go all the way to the shared ViewModel route if the behavior is based purely on which route you are on. If you want it to be based on some state local to the destination (that you want saved properly), that’s where it gets trickier.