With the following code:

val groupLazyListState = rememberLazyListState()

val topBarBackgroundAlpha by remember(groupLazyListState) {
    derivedStateOf {
        val layoutInfo = groupLazyListState.layoutInfo
        val itemInfo = layoutInfo.visibleItemsInfo
            .firstOrNull { it.contentType == ImmersiveCollectionUiModel::class }
            ?: return@derivedStateOf 1f

        val adjustedOffset = itemInfo.offset.absoluteValue - layoutInfo.viewportStartOffset
        adjustedOffset / itemInfo.size.toFloat()
    }
}

I have some top menu items where I completely switch the following

Group

composable. This ends up being totally new

LazyColumns

underneath, but using the same

LazyListState

.

Group(
    model = group,
    lazyListState = groupLazyListState,
)

When I’m switching between these menu items, I’ll end up in a state where

derivedStateOf

stops being called and my

topBarBackgroundAlpha

no longer changes.

Group

is totally fine, scroll is working fine, its just that observing those scroll state changes will no longer work. What am I missing here?

I guess the issue must be similar to https://issuetracker.google.com/issues/294436482

rememberUpdatedState

seems to solve it, but its not very obvious right away why

derivedStateOf

doesn’t retrigger on updated

layoutInfo

.