I have ```val listState = rememberLazyListState ``` and I us

Question

I have ```val listState = rememberLazyListState ``` and I use it with `LazyColumn` and it works fine composable function is executed once The problem is when I try to check visible elements and I call `listState layoutInfo` Then composable function is recalled state was changed and view is regenerated Why

Alexander Maryanovsky · Answer

Can you post a short example

bartosz.malkowski · Answer

Sure Here it is <https github com bmalkow ListStateProblemDemo>

Alexander Maryanovsky · Answer

Not sure I understand the problem That s how state in compose works Whenever you read a state value inside a Composable function and that state changes the function will get called to re create the UI this all roughly speaking the details are somewhat more complex

bartosz.malkowski · Answer

Yup Keyword read a state slightly smiling face State is not modified I just want to check if element is visible or not But it causes recalling whole function and few times bigger CPU usage

Alexander Maryanovsky · Answer

That state is modified during layout

Alexander Maryanovsky · Answer

Not by you

Alexander Maryanovsky · Answer

If you want your UI to depend on a function of the state whose output changes less frequently than the state itself look into derivedState

bartosz.malkowski · Answer

Like this ```val listState by remember derivedStateOf LazyListState ``` If yes then it doesn t help

Alexander Maryanovsky · Answer

No not like that Define the list state normally

Alexander Maryanovsky · Answer

But then say you want to show the number of visible items Use val itemCount by derivedStateOf listState layoutInfo visibleItems size

Alexander Maryanovsky · Answer

Then the code that reads itemCount will only be called when the value of itemCount changes instead of whenever layoutInfo changes

Alexander Maryanovsky · Answer

and just for future questions this is more appropriate for the general < CJLTWPH7S|compose> channel since it s not specifically about compose on the desktop

bartosz.malkowski · Answer

I wasn t sure it is problem of Desktop itself slightly smiling face

bartosz.malkowski · Answer

Anyway with derived state `List ` is called twice what is good for me slightly smiling face Thanks a lot for help and explanation

Alexander Maryanovsky · Answer

You re welcome Also don t worry about extra recompositions too much unless they re causing a measurable problem for you

Alexander Maryanovsky · Answer

That s the guideline anyway

bartosz.malkowski · Answer

Right it is not problem for me when function is called twice in this example with visible items equals `0` and `6` Problem is when function is called in infinite loop because of wrong way of reading visible items size slightly smiling face