Some composables swipeable BottomSheet HorizontalPager LazyC

Question

Some composables swipeable BottomSheet HorizontalPager LazyColumn etc have some internal state which they manage by themselves and even when this state is allowed to be hoisted the need for detecting some events based on state changes arises I find myself wishing to write `if prevState = 1 amp amp state = 0 onEvent ` Sometimes this leads me to discovery that I think about the state wrong and I refactor but sometimes I can t and I ask myself what s the best pattern to detect some thresholds in state changes Examples ListColumn has just scrolled past 100 visible item how to report this to analytics Composable with `swipeable` modifier has just finished settling after swipe How to observe this change from `swipeableState isAnimationRunning` from `true` to `false` and report it to some other component

dimsuz · Answer

for swipeable example I tried ```log is animating $ swipeableState isAnimationRunning val flow = snapshotFlow swipeableState isAnimationRunning LaunchedEffect Unit flow collect log animated changed to $ it ``` this logs a lot of is animating which changes from `false` to `true` to `false` but animated changed is logged only once as start as `false` So I guess snapshotFlow is not for this usecase or maybe it s even an antipattern here What s the right way to go then

Zach Klippenstein (he/him) [MOD] · Answer

Two things that I don t think are related to this issue but are anti patterns nonetheless 1 You should create the snapshot flow inside the launched effect if that s the only place you re using it from Otherwise you re creating a new flow on every recomposition but only using the first one The rest are just discarded so creating them is pointless 2 Always pass dependencies to your effect as keys In this case your effect has a dependency on swipeableState so it should be passed You almost never want to use `Unit`

dimsuz · Answer

oh both valid points I have tried the first but failed at the second It works now So answering a more generic question using `snapshotFlow` for those cases is a valid way to go

Zach Klippenstein (he/him) [MOD] · Answer

That is surprising it means you re actually getting a different swipeableState object whenever the animation changes but the state should live longer than that How are you creating your swipeable state

Zach Klippenstein (he/him) [MOD] · Answer

But yea to detect state changes like this you could use flow operators something like ```snapshotFlow state distinctUntilChanged drop 1 filter it == 0 ``` Or ```snapshotFlow state scan prev new gt prev == 1 amp amp new == 0 distinctUntilChanged ```

dimsuz · Answer

```val swipeableState = rememberSwipeableState initialValue = findInitialAnchorId state value LaunchedEffect swipeableState val flow = snapshotFlow swipeableState isAnimationRunning flow collect Timber e animated changed to $ it ``` This works I have logged swipeableState and it doesn t change object hex pointer so it s the same