Question: given a LazyColumn with many items, how ...

# compose

[eneim]

Question: given a LazyColumn with many items, how can I collect the indexes of items that user has scrolled through without using a Composable (e.g. storing them to Database)? I tried the side effects:

// Use the index as key to be notified when it is changed.
LaunchedEffect(key1 = listState.firstVisibleItemIndex) {
    // Store the listState.firstVisibleItemIndex to DB
}

But it slows down the scroll performance significantly.

[Albert Chang]

You can use snapshotFlow { listState.firstVisibleItemIndex }.collect().

[eneim]

Oh, from where should I call the snapshotFlow ? It is a global scope method.

[Albert Chang]

Something like:

val listState = rememberLazyListState()
LaunchedEffect(listState) {
    snapshotFlow { listState.firstVisibleItemIndex }.collect { index ->
        // Save to DB
    }
}

[eneim]

Thanks a lot @Albert Chang, somehow I manage to do the same. Do you know any link to the document that mention the snapshotFlow? I want to make sure it is noted somewhere that I just happen to not read yet.

[Albert Chang]

Mentioned here: https://developer.android.com/jetpack/compose/lists#react-to-scroll-position