LazyColumn composition clarification

Question

I was playing around with the LazyColumn composable to implement a collapsing toolbar behavior with a sticky header. I then realized that the Lazycolumn is constantly rendering the items and never stopping doing so. As an example the code below(can't do any easier than that) would give me the logcat below:

@Composable
fun Scanner() {


    val listState = rememberLazyListState()
    val list = listOf(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)

    LazyColumn(
        modifier = Modifier
            .background(MaterialTheme.colors.background)
            .wrapContentHeight()
            .fillMaxWidth(),
        state = listState,
        contentPadding = PaddingValues(start = 1.dp, end = 1.dp, bottom = 1.dp),
        verticalArrangement = Arrangement.spacedBy(8.dp),
        ) {

        itemsIndexed(list){index, item ->

            key(index){

                Card(
                    modifier = Modifier
                        .padding(5.dp)
                        .fillMaxWidth()
                        .height(50.dp),
                    elevation = 0.dp,

                    ) {

                    Log.d("Lazy ColumScanner", "Composing:$item ")

                    Text(
                        text = "$item",
                        fontSize = 25.sp
                    )
                  
                }
            }
        }
    }
}

2021-07-13 19:29:15.025 14066-14072/com.paulhugon.digipaule I/zygote: Increasing code cache capacity to 512KB
2021-07-13 19:29:15.123 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:0 
2021-07-13 19:29:15.153 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:1 
2021-07-13 19:29:15.174 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:2 
2021-07-13 19:29:15.199 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:3 
2021-07-13 19:29:15.222 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:4 
2021-07-13 19:29:15.244 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:5 
2021-07-13 19:29:15.264 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:6 
2021-07-13 19:29:15.283 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:7 
2021-07-13 19:29:15.456 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:0 
2021-07-13 19:29:15.461 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:1 
2021-07-13 19:29:15.468 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:2 
2021-07-13 19:29:15.473 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:3 
2021-07-13 19:29:15.478 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:4 
2021-07-13 19:29:15.485 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:5 
2021-07-13 19:29:15.491 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:6 
2021-07-13 19:29:15.498 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:7 
2021-07-13 19:29:15.567 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:0 
2021-07-13 19:29:15.573 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:1 
2021-07-13 19:29:15.579 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:2 
2021-07-13 19:29:15.585 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:3 
2021-07-13 19:29:15.589 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:4 
2021-07-13 19:29:15.594 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:5 
2021-07-13 19:29:15.599 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:6 
2021-07-13 19:29:15.604 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:7 
2021-07-13 19:29:15.605 14066-14072/com.paulhugon.digipaule I/zygote: Do full code cache collection, code=252KB, data=221KB
2021-07-13 19:29:15.607 14066-14072/com.paulhugon.digipaule I/zygote: After code cache collection, code=221KB, data=165KB
2021-07-13 19:29:15.646 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:0 
2021-07-13 19:29:15.650 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:1 
2021-07-13 19:29:15.653 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:2 
2021-07-13 19:29:15.657 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:3 
2021-07-13 19:29:15.661 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:4 
2021-07-13 19:29:15.664 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:5 
2021-07-13 19:29:15.668 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:6 
2021-07-13 19:29:15.672 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:7 
2021-07-13 19:29:15.717 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:0 
2021-07-13 19:29:15.722 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:1 
2021-07-13 19:29:15.726 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:2 
2021-07-13 19:29:15.730 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:3 
2021-07-13 19:29:15.734 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:4 
2021-07-13 19:29:15.737 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:5 
2021-07-13 19:29:15.741 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:6 
2021-07-13 19:29:15.745 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:7 
2021-07-13 19:29:15.793 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:0 
2021-07-13 19:29:15.797 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:1 
2021-07-13 19:29:15.802 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:2 
2021-07-13 19:29:15.806 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:3 
2021-07-13 19:29:15.810 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:4 
2021-07-13 19:29:15.814 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:5 
2021-07-13 19:29:15.818 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:6 
2021-07-13 19:29:15.823 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:7 
2021-07-13 19:29:15.870 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:0 
2021-07-13 19:29:15.874 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:1 
2021-07-13 19:29:15.878 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:2 
2021-07-13 19:29:15.883 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:3 
2021-07-13 19:29:15.886 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:4 
2021-07-13 19:29:15.891 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:5 
2021-07-13 19:29:15.896 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:6 
2021-07-13 19:29:15.899 14066-14066/com.paulhugon.digipaule D/Lazy ColumScanner: Composing:7

I cut the logcat for the question length sake but it goes on and on as long as the app is on.... This is on jetpack-compose version beta09. Is it a normal behavior or is it normal that it sounds weird to me that the composable inside the LazyColumn is (re)composed indefinitely? Hopefully someone can share some light on that matter. Thanks for your time

Could you try ditching that ```listState``` variable and then check the logs? — Richard Onslow Roper, Jul 13 '21 at 17:58
Are you getting the same logs even if you don't scroll the list? — sitatech, Jul 13 '21 at 18:15
@MARSK ok without the rememberlazylist it is indeed as it should be. I need this rememberlazylist though...any idea why it is doing that? — Paul-E, Jul 13 '21 at 18:30
I ran your code without making any change, I'm not facing any error, the log message shows only the visible items and updates when I scroll. I'm using the 1.0.0 release candidate of compose. try upgrading your dependencies. — sitatech, Jul 13 '21 at 21:08
@sitatech indeed it's working with 1.0.0-rc01. is it a known bug in beta09? — Paul-E, Jul 13 '21 at 21:21

LazyColumn composition clarification

0 Answers0