Hey folks has anyone run into the case with the LazyColumn w

Question

Hey folks has anyone run into the case with the LazyColumn where mutating the backing list causes each item in the list to be recomposed Attached is a video example which uses the <https raw githubusercontent com android snippets master compose recomposehighlighter src main java com example android compose recomposehighlighter RecomposeHighlighter kt|compose highlighter> to track recompositions You ll notice that when I tap the item it adds a new item to the list but the entire list recomposes Minimal example is in the thread below

karn · Answer

``` Use recomposeHighlighter from <https github com android snippets blob master compose recomposehighlighter src main java com example android compose recomposehighlighter RecomposeHighlighter kt> class MainActivity ComponentActivity override fun onCreate savedInstanceState Bundle super onCreate savedInstanceState setContent MyApplicationTheme val mutableState = remember mutableStateOf listOf 1 2 3 LazyColumn state = rememberLazyListState modifier = Modifier fillMaxWidth itemsIndexed items = mutableState value key = index Int item Int gt item index item gt Text modifier = Modifier recomposeHighlighter clickable mutableState value = mutableState value + Random nextInt 3 100000 text = $item ```

myanmarking · Answer

Yes thats expected because every item reads the state

myanmarking · Answer

Extract the mutableState to outside the lazycolumn and use a lambda to update the value It should fix the problem

Dan Yang · Answer

Interesting question I was also able to repro but I don t know enough about compose to describe why I tried < myanmarking> s suggestion but I don t know how you d be able to extract the `mutableState` if it s used to back the `lazyColumn` s collection The closest I got was extracting the `mustableState` reference in the `clickable` but it still causes the whole list to recompose ```val mutableState = remember mutableStateOf listOf 1 2 3 val textClickable = remember mutableState value = mutableState value + Random nextInt 3 100000 LazyColumn state = rememberLazyListState modifier = Modifier fillMaxWidth itemsIndexed items = mutableState value key = index Int item Int gt item index item gt Text modifier = Modifier recomposeHighlighter clickable onClick = textClickable text = $item ```

myanmarking · Answer

Yes I don t know why the text get s recomposed in your code above But extracting the text composable to a separate one solves the problem My guess is that List lt gt is not stable so it schedules the recompose on all the children but for some reason Text won t skip when it should because string is the same Code below does that Idk maybe some expert can explain this

myanmarking · Answer

`var mutableState List lt Int gt by remember ` `mutableStateOf ` `listOf 1 2 3 ` ` ` ` ` `val onClick = ` `mutableState = mutableState + Random nextInt 3 100000 ` ` ` `LazyColumn ` `state = rememberLazyListState ` `modifier = Modifier fillMaxWidth ` ` ` `itemsIndexed ` `items = mutableState ` `key = Int item Int gt item ` ` item gt ` `MyText ` `label = item toString ` `onClick = onClick` ` ` ` ` ` ` ` Composable` `private fun MyText ` `label String ` `onClick gt Unit` ` ` `Text ` `modifier = Modifier` ` fillMaxWidth ` ` padding vertical = 5 dp ` ` recomposeHighlighter ` ` clickable onClick = onClick ` `text = label` ` ` ` `

Dan Yang · Answer

You re right That s so interesting I think this has to do `skippable` composables From <https github com androidx androidx blob androidx main compose compiler design compiler metrics md functions that are restartable but not skippable> gt Skippability means that when called during recomposition compose is able to skip the function if all of the parameters are equal When split out `MyText` is `skippable` but perhaps `LazyColumn` is not skippable maybe because of the `List lt gt ` therefore the whole function body is run I tried changing `MyText` to take a non stable param and it started recomposing when I clicked on the text again ```data class Data val item Int Composable fun SpecialText item Data textClickable gt Unit Text modifier = Modifier recomposeHighlighter clickable onClick = textClickable text = $item ```