Hi everyone I’m doing horizontal pager infinite l...

# compose

[Toan Nguyen]

Hi everyone
I’m doing horizontal pager infinite loop and i see this bug. When i add job animateScrollToPage in LaunchedEffect , the screen will show 1/2 ui pager when job is working. But when i add job animateScrollToPage in coroutineScope , it’ll work correct. This is bug LauncherEffect in compose? So somebody can explain me the reason?

[Yann Badoual]

Check if pagerState.currentPage is changing before the animation is completed. It would cause the LaunchedEffect block to be cancelled (and thus the animation)

You can also use a snapshotFlow on currentPage to observe and scroll (removing the key from LaunchedEffect would fix the bug + avoid unnecessary recomposition)

[Toan Nguyen]

@Yann Badoual you mean i should use snapshotFlow instead of launcherEffect? I’m doing flow your answer but it still happen. Can u give me example code 😂 .

[xoangon]

The adequate scope to update the pager state should be a CoroutineScope obtained using rememberCoroutineScope. The reason is that LaunchedEffect is only triggered when you enter the composition phase, but a remembered CoroutineScope could be used to trigger async events at any other point outside of composition.

This article by @Jorge Castillo explains it pretty neatly --> https://newsletter.jorgecastillo.dev/p/jetpack-compose-effect-handlers

[xoangon]

This other article is helpful for understanding that difference:

https://proandroiddev.com/launchedeffect-vs-remembercoroutinescope-in-jetpack-compose-24b5c91106ac

[Toan Nguyen]

@xoangon Oh very helpful for me. Thank you a lot 😄