Can someone share insights on how to use `rememberLazyListState` with `LazyColumn` for a chat interf...

# compose

[Sam]

Can someone share insights on how to use rememberLazyListState with LazyColumn for a chat interface? JetChat in compose-samples still uses ScrollableColumn so it doesn’’t help much, especially in these areas:
• How do we smooth scroll to show a new incoming message? Since we only have relative-based smoothScrollBy instead of smoothScrollTo(0f) (on reverseLayout = true), it’s hard to get to the right spot and snapToIndex(0) is unnatural
• How do we get measurements of the specific message component sizes to make the right relative scrolling calculation? I’ve seen chatScrollState.layoutInfo.visibleItemsInfo but i’m not sure how to get updates when layoutInfo changes, sticking it inside LaunchedEffect doesn’t fire
• How do we know when we are getting to the end of the LazyColumn so that we can fetch older messages and add them to the list?
• In the case where new messages are coming in or old messages are being added, how do we maintain existing scroll position without the whole list jumping around?

[Sam]

cc @Andrey Kulikov

[Dominaezzz]

I also happen to be interested in this too and have implement some.

[Dominaezzz]

For the 3rd point you can use onActive { onDispose {} } on the oldest (or whatever you feel is right) item in the LazyColumn to trigger the fetch.

[Dominaezzz]

For the second point, try using a snapshotFlow { .... } to capture the changes.

[Dominaezzz]

For the first point, it's a relatively new feature so I'm not sure. In theory you can use keep calling smoothScrollBy until you're at the bottom of the list aha.

[Dominaezzz]

For the last point, when I get new messages I don't experience this jumping you describe.

[Sam]

@Dominaezzz good suggestion to support infinite scroll, i will try adding logic to onActive to detect when to fetch

[Sam]

@Dominaezzz are you using reverseLayout = true? If so, how do you show new messages that just arrived, snapToIndex or smoothScrollBy ?

[Dominaezzz]

I am indeed using reverseLayout = true new messages tend to just show up without me having to scroll. Although if there's a tiny bit of scroll, it doesn't show up. Haven't gotten to that yet.

[Sam]

but do they smooth scroll or they just snap and appear?

[Dominaezzz]

It's a snap. I'm pretty sure most messengers do this though.

[Sam]

i don’t know about android, but there isn’t a single one on iOS that snaps

[Dominaezzz]

Fascinating. Slack snaps

[Dominaezzz]

Unless you're on iOS now lol.

[Sam]

most chat apps snap on desktop, but not on iOS

[Andrey Kulikov]

smoothScrollToItem is still in progress, so not yet ready. we also don’t yet have a solid support for item animations, you can implement something on your own with tools like AnimatedVisibility, but not everything