Found interesting behaviour of Material3 `BottomSheetScaffold` and `NavHost` App is using `NavHost` ...

# compose

[Tomas Škarnulis]

Found interesting behaviour of Material3 BottomSheetScaffold and NavHost
App is using NavHost that has nested navigation inside where few screens will be attached to main NavHost, and other smaller one - to BottomSheetScaffold NavHost

In first init of the screen bottom sheet can not be hidden on swipe.
Then, if we navigate from nav graph that has bottom sheet to other navigation - on back BottomSheetScaffold can be hidden. 😄

Other thing, if we leave screen with BottomSheetScaffold expanded - on back we will get :

IllegalStateException - If the offset has not been initialized yet

I am assuming that NavHost somehow recreates screen maybe, and rememberStandardBottomSheetState initialised again... Still figuring this out, just wanted to share maybe someone already solved similar situation to this and can give some tips where to look

Screen Recording 2023-09-23 at 13.22.03.mov

[Tomas Škarnulis]

Quick LaunchedEffect(Unit) show that states is really recreated on back:

MapAndBottomSheet: creation
MapAndBottomSheet: botSheet 131380672
MapAndBottomSheet: scaffold: 124916473

....

MapAndBottomSheet: creation
MapAndBottomSheet: botSheet 195691014
MapAndBottomSheet: scaffold: 178577607

[Tomas Škarnulis]

So i hacked my way like this:
rememberStandardBottomSheetState set skipHiddenState to false - this will always let bottom sheet to be hidden on swipe

Than use rememberSaveable to save last know SheetValue on confirmValueChange in rememberStandardBottomSheetState

than I use LaunchedEffect(lastBootomSheetState) and check last and current sheet value, and if its not a same - I use last value to move bottom sheet + save last = current

Hacky, so will check if it has any issues here

[Tomas Škarnulis]

Screen Recording 2023-09-23 at 15.55.56.mov

Screen Recording 2023-09-23 at 15.55.56.mov

[Patrick Steiger]

It’s been a while since I used NavHost but the assumption that previous nav entries are destroyed and recreated is correct (at least it was back then)

Navigation relies on SavedState mechanism to restore state when navigating back to some destinations

[jossiwolf]

Which version is this on?

[Tomas Škarnulis]

androidx.compose.material3:material3:1.2.0-alpha08
androidx.navigation:navigation-compose:2.7.0-beta02
Kotlin version: 1.8.20

[jossiwolf]

Please file an issue with a repro!