Problem using LaunchedEffect scope in jetpack compose

Question

I have two LaunchedEffect scopes like this :

 LaunchedEffect(key1 = mainViewModel.myvlue.value){ mainViewModel.updatemyvalue(1f) } LaunchedEffect(key1 = mainViewModel.myvlue.value){ mainViewModel.updatemyvalue(0f) }

Both are implemented inside this method :

@Composable fun TabContent( pagerState: PagerState,count:Int,mainViewModel: MainViewModel) { HorizontalPager(state = pagerState, count = count) { index -> when (index) { 0 -> { LaunchedEffect(key1 = mainViewModel.myvlue.value){ mainViewModel.updatemyvalue(1f) } SecondScreen(mainViewModel) } 1 -> { LaunchedEffect(key1 = mainViewModel.myvalue.value) { mainViewModel.updatemyvalue(0f) } firstScreen(mainViewModel) } } } }

The problem is that when one of these scopes launches, second one will be automatically called .

I know this is normal that when the key1 value changes scopes will be relaunched . but I just want them to be called separately when I navigate to their respective page inside HorizontalPager.

As you can see above, they will be called simultaneously when one of the executes.

what should I do ?

It is not clear why you should use a side effect in this way clicking a button. — Gabriele Mariotti
– Gabriele Mariotti, Commented Feb 8, 2023 at 22:51
Why not just remove the LaunchedEffects, are they needed for some reason? — CCT
– CCT, Commented Feb 8, 2023 at 23:42
Compose code needs to be side effect free. Because Composables can run at any time, in parallel or not at all. If I do not use this block, My code is not guaranteed to be executed at all. More info : developer.android.com/jetpack/compose/mental-model#parallel — A.G
– A.G, Commented Feb 9, 2023 at 0:03
Have you tried moving LaunchedEffects out of the HorizontalPager, then use a boolean to determine which to use. LaunchedEffect(yourBoolean){ ..., set the boolean to true or false in your HorizontalPager and it should trigger the LaunchedEffect when true or when false for the second Launched Effect — CCT
– CCT, Commented Feb 9, 2023 at 0:46

Vahid Garousi · Accepted Answer · 2023-02-09 04:28:26Z

You should use the current index below in the way I posted in the attachment

Please test

// Page change callback LaunchedEffect(pagerState) { snapshotFlow { pagerState.currentPage }.collect { page -> when (page) { 0 -> viewModel.updatemyvalue() // First page 1 -> // Second page else -> // Other pages } } }

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