Is it expected Behavior to recompose the items of ...

# compose

[Shakil Karim]

Is it expected Behavior to recompose the items of LazyColumn on each scroll event ? I was try to log the composition count

LazyColumn(
    state = scrollState,
    modifier = Modifier.fillMaxSize()
) {
    item {
        LogCompositions("CompetitionDetailsScreenNew header")
         //Some item
     }
}

[Andrey Kulikov]

now, only the new items should be composed when you scroll to them. could you please show more code, more specifically how else do you use scrollState

[Shakil Karim]

@Andrey Kulikov I'm using LazyColumn like this
https://gist.github.com/shakil807g/98c68f81b91d464d469aa8f7002ba8dd
item is calling continuously as I scroll, which I guess is the main cause of frame skips.
https://gist.github.com/shakil807g/98c68f81b91d464d469aa8f7002ba8dd#file-competitiondetailsscreennew-kt-L36

[Andrey Kulikov]

could you please move collapseFraction calculation right where it is used, inside graphicsLayer { .. here .. }

[Andrey Kulikov]

in this case on every scrollState.firstVisibleItemScrollOffset update (every scroll) instead of doing recomposition we will only need to update a params on graphics layer, which is very cheap

[Andrey Kulikov]

if in future you will anyway need to recompose when something like this changes you can all least make it recompose less often with trick like this:
instead of

val collapseFraction =
    (scrollState.firstVisibleItemScrollOffset / collapseRange).coerceIn(0f, 1f)

you do:

val collapseFraction = remember(collapseRange) {
    derivedStateOf { (scrollState.firstVisibleItemScrollOffset / collapseRange).coerceIn(0f, 1f) }
}

and now when you use collapseFraction.value this value is only recomposed when the resulting float fraction changes.

[Shakil Karim]

Thanks, i updated my code, but it seems item are recompose only when they are become visible again after scrolling. Performance is still an issue.

[Andrey Kulikov]

do you mean items are composed only when the new item became visible? it is expected behaviour. and yes, there are some performance to be made on our side in next releases as well