Paging in Compose-Listen

Seitennummerierte Daten in Compose rendern

collectAsLazyPagingItems

import androidx.paging.compose.collectAsLazyPagingItems

@Composable
fun ArticleScreen(viewModel: ArticleViewModel) {
    val articles = viewModel.articles.collectAsLazyPagingItems()
    ArticleList(articles)
}

items() mit LazyPagingItems

import androidx.compose.foundation.lazy.LazyColumn
import androidx.paging.compose.LazyPagingItems
import androidx.paging.compose.items

@Composable
fun ArticleList(articles: LazyPagingItems<Article>) {
    LazyColumn {
        items(articles) { article ->
            if (article != null) {
                ArticleRow(article)
            }
        }
    }
}

Stabile Schlüssel für Elemente

import androidx.paging.compose.itemKey

LazyColumn {
    items(
        count = articles.itemCount,
        key = articles.itemKey { it.id }
    ) { index ->
        val article = articles[index]
        if (article != null) ArticleRow(article)
    }
}

Ladezustände auslesen

import androidx.paging.LoadState

val refresh = articles.loadState.refresh
val append = articles.loadState.append

val isInitialLoading = refresh is LoadState.Loading
val isLoadingMore = append is LoadState.Loading

Lade- und Leerzustände im Vollbild

when (val refresh = articles.loadState.refresh) {
    is LoadState.Loading -> FullScreenSpinner()
    is LoadState.Error -> FullScreenError(
        message = refresh.error.message,
        onRetry = { articles.retry() }
    )
    is LoadState.NotLoading -> {
        if (articles.itemCount == 0) EmptyState()
        else ArticleList(articles)
    }
}

Ladekreisel am unteren Rand beim Anhängen

LazyColumn {
    items(count = articles.itemCount, key = articles.itemKey { it.id }) { index ->
        articles[index]?.let { ArticleRow(it) }
    }

    if (articles.loadState.append is LoadState.Loading) {
        item {
            Box(Modifier.fillMaxWidth().padding(16.dp), Alignment.Center) {
                CircularProgressIndicator()
            }
        }
    }
}

Bei Fehlern erneut versuchen

val append = articles.loadState.append
if (append is LoadState.Error) {
    item {
        Row(Modifier.fillMaxWidth().padding(16.dp), Arrangement.Center) {
            Text("Couldn't load more")
            Spacer(Modifier.width(8.dp))
            Button(onClick = { articles.retry() }) { Text("Retry") }
        }
    }
}

Durch Herunterziehen aktualisieren

import androidx.compose.material3.pulltorefresh.PullToRefreshBox

val isRefreshing = articles.loadState.refresh is LoadState.Loading
PullToRefreshBox(
    isRefreshing = isRefreshing,
    onRefresh = { articles.refresh() }
) {
    ArticleList(articles)
}

Kopfzeile und Trennlinien

LazyColumn {
    item { SearchBar(query, onQueryChange) }

    items(count = articles.itemCount, key = articles.itemKey { it.id }) { index ->
        val article = articles[index]
        if (article != null) {
            ArticleRow(article)
            HorizontalDivider()
        }
    }

    if (articles.loadState.append.endOfPaginationReached) {
        item { Text("You're all caught up", Modifier.padding(16.dp)) }
    }
}

Seitennummerierte Listen in der Vorschau

import androidx.paging.PagingData
import kotlinx.coroutines.flow.flowOf

@Preview
@Composable
fun ArticleListPreview() {
    val sample = listOf(Article(1, "Hello"), Article(2, "World"))
    val flow = flowOf(PagingData.from(sample))
    ArticleList(flow.collectAsLazyPagingItems())
}

Kurze Überprüfung

Zusammenfassung: Paging in Compose