Jetpack Compose 的 LazyVerticalGrid 是否有跨度策略

Question

I have a LazyVerticalGrid with 2 cells.

LazyVerticalGrid(
    cells = GridCells.Fixed(2),
    content = {
        items(moviePagingItems.itemCount) { index ->
            val movie = moviePagingItems[index] ?: return@items
            MovieItem(movie, Modifier.preferredHeight(320.dp))
        }
        renderLoading(moviePagingItems.loadState)
    }
)

I am trying to show full width loading with LazyGridScope 's fillParentMaxSize modifier.

fun LazyGridScope.renderLoading(loadState: CombinedLoadStates) {
  when {
    loadState.refresh is LoadState.Loading -> {
        item {
            LoadingColumn("Fetching movies", Modifier.fillParentMaxSize())
        }
    }
    loadState.append is LoadState.Loading -> {
        item {
            LoadingRow(title = "Fetching more movies")
        }
    }
  }
}

But since we have 2 cells, the loading can occupy half of the screen. Like this:

Is there a way my loading view can occupy full width?

Answer 1

LazyVerticalGrid has a span strategy built into items() and itemsIndexed()

@Composable
fun SpanLazyVerticalGrid(cols: Int, itemList: List<String>) {
    val lazyGridState = rememberLazyGridState()
    LazyVerticalGrid(
            columns = GridCells.Fixed(cols),
            state = lazyGridState
    ) {
        items(itemList, span = { item ->
            val lowercase = item.lowercase()
            val span = if (lowercase.startsWith("a") || lowercase.lowercase().startsWith("b") || lowercase.lowercase().startsWith("d")) {
                cols
            }
            else {
                1
            }
            GridItemSpan(span)
        }) { item ->
            Box(modifier = Modifier
                    .fillMaxWidth()
                    .height(150.dp)
                    .padding(10.dp)
                    .background(Color.Black)
                    .padding(2.dp)
                    .background(Color.White)
            ) {
                Text(
                        modifier = Modifier.align(Alignment.Center),
                        text = item,
                        fontSize = 18.sp
                )
            }
        }
    }
}

'

val names = listOf("Alice", "Bob", "Cindy", "Doug", "Ernie", "Fred", "George", "Harris")
SpanLazyVerticalGrid(
        cols = 3,
        itemList = names
)

Answer 2

Try something like:

var cellState by remember { mutableStateOf(2) }
LazyVerticalGrid(
    cells = GridCells.Fixed(cellState),
    content = {
        items(moviePagingItems.itemCount) { index ->
            val movie = moviePagingItems[index] ?: return@items
            MovieItem(movie, Modifier.preferredHeight(320.dp))
        }
        renderLoading(moviePagingItems.loadState) {
            cellState = it
        }
    }
)

The renderLoading function:

fun LazyGridScope.renderLoading(loadState: CombinedLoadStates, span: (Int) -> Unit) {
    when {
        loadState.refresh is LoadState.Loading -> {
            item {
                LoadingColumn("Fetching movies", Modifier.fillParentMaxSize())
            }
            span(1)
        }
        ...
        else -> span(2)
    }
  
}

Answer 3

I have created an issue for it: https://issuetracker.google.com/u/1/issues/176758183

Current workaround I have is to use LazyColumn and implement items or header.

override val content: @Composable () -> Unit = {
    LazyColumn(
            contentPadding = PaddingValues(8.dp),
            content = {
                items(colors.chunked(3), itemContent = {

                    Row(horizontalArrangement = Arrangement.SpaceEvenly) {
                        val modifier = Modifier.weight(1f)
                        it.forEach {
                            ColorItem(modifier, it)
                        }
                        for (i in 1..(3 - it.size)) {
                            Spacer(modifier)
                        }
                    }
                })
                item {
                    Text(
                            text = stringResource(R.string.themed_colors),
                            style = MaterialTheme.typography.h3
                    )
                }
                items(themedColors.chunked(3), itemContent = {
                    Row(horizontalArrangement = Arrangement.SpaceEvenly) {
                        val modifier = Modifier.weight(1f)
                        it.forEach {
                            ColorItem(modifier, it)
                        }
                        for (i in 1..(3 - it.size)) {
                            Spacer(modifier)
                        }
                    }
                })
            })
}

Answer 4

Jetpack Compose 1.1.0-beta03 version includes horizontal span support for LazyVerticalGrid .

Here is the example usage:

private const val CELL_COUNT = 2

private val span: (LazyGridItemSpanScope) -> GridItemSpan = { GridItemSpan(CELL_COUNT) }

LazyVerticalGrid(
    cells = GridCells.Fixed(CELL_COUNT),
    content = {
        items(moviePagingItems.itemCount) { index ->
            val movie = moviePagingItems.peek(index) ?: return@items
            Movie(movie)
        }
        renderLoading(moviePagingItems.loadState)
    }
}

private fun LazyGridScope.renderLoading(loadState: CombinedLoadStates) {
    if (loadState.append !is LoadState.Loading) return

    item(span = span) {
        val title = stringResource(R.string.fetching_more_movies)
        LoadingRow(title = title)
    }
}

Code examples of this answer can be found at: Jetflix/MoviesGrid.kt