I want to use Column instead of LazyColumn, and make it scrollable by Modifier.verticalScroll(scrollState) , is there any way to get currently visible items key that users see on the screen?

CodePudding user response：

I'm not positive that I fully understand, so this may be off base but here's some code that keeps track of the position of the items within a scrollable column and updates a text whenever the first visible item changes. Performance seems okay, at least for a list of items that would be reasonable for a non-lazy column.

@Composable
fun Example() {
    val positions = remember { items.map { 0f }.toMutableStateList() }

    val ss = rememberScrollState()
    val firstVisibleItem by remember {
        derivedStateOf {
            positions.indexOfLast {
                it <= ss.value
            }
        }
    }
    Column(Modifier.fillMaxSize()) {
        Text(
            items.getOrElse(firstVisibleItem) { "None "},
            Modifier
                .fillMaxWidth()
                .background(Color.LightGray)
                .padding(16.dp)
        )
        Column(
            Modifier
                .verticalScroll(ss)
                .fillMaxSize()
                .padding(16.dp)
        ) {
            items.forEachIndexed { index, item ->
                Text(
                    text = item,
                    modifier = Modifier
                        .height(100.dp)
                        .onGloballyPositioned {
                            positions[index] = it.positionInParent().y
                        }
                )
            }
        }
    }
}

As an aside, I'd be surprised if a normal scrollable column had better performance than a lazy one unless the item count is very small.