androidx.paging.compose

Common/All

Classes

LazyPagingItems

The class responsible for accessing the data from a Flow of PagingData.

Cmn

Composables

collectAsLazyPagingItems

Collects values from this Flow of PagingData and represents them inside a LazyPagingItems instance.

Cmn

Extension functions summary

(index: Int) -> Any?	<T : Any> LazyPagingItems<T>.itemContentType(contentType: ((item) -> Any?)?) Returns a factory for the content type of the item.	Cmn
(index: Int) -> Any	<T : Any> LazyPagingItems<T>.itemKey(key: ((item) -> Any)?) Returns a factory of stable and unique keys representing the item.	Cmn

Extension functions

LazyPagingItems.itemContentType

Cmn

Artifact: androidx.paging:paging-compose

View Source

fun <T : Any> LazyPagingItems<T>.itemContentType(
    contentType: ((item) -> Any?)? = null
): (index: Int) -> Any?

Returns a factory for the content type of the item.

ContentTypes are generated with the contentType lambda that is passed in. If null is passed in, contentType of all items will default to null. If PagingConfig.enablePlaceholders is true, LazyPagingItems may return null items. Null items will automatically default to placeholder contentType.

This factory can be applied to Lazy foundations such as LazyGridScope.items or Pagers. Examples:

import androidx.compose.foundation.lazy.grid.GridCells
import androidx.compose.foundation.lazy.grid.LazyVerticalGrid
import androidx.paging.compose.collectAsLazyPagingItems
import androidx.paging.compose.itemContentType
import androidx.paging.compose.itemKey

val lazyPagingItems = pager.collectAsLazyPagingItems()

LazyVerticalGrid(columns = GridCells.Fixed(2)) {
    items(
        count = lazyPagingItems.itemCount,
        key = lazyPagingItems.itemKey { it },
        contentType = lazyPagingItems.itemContentType { "MyPagingItems" },
    ) { index ->
        val item = lazyPagingItems[index]
        PagingItem(item = item)
    }
}

import androidx.compose.foundation.background
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.foundation.layout.padding
import androidx.compose.foundation.lazy.LazyColumn
import androidx.compose.material.Text
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.unit.dp
import androidx.compose.ui.unit.sp
import androidx.paging.compose.collectAsLazyPagingItems
import androidx.paging.compose.itemContentType
import androidx.paging.compose.itemKey

val lazyPagingItems = pager.collectAsLazyPagingItems()

LazyColumn {
    stickyHeader(key = "Header", contentType = "My Header") {
        Box(
            modifier = Modifier.padding(bottom = 10.dp).background(Color.Red).fillMaxWidth(),
            contentAlignment = Alignment.Center,
        ) {
            Text(text = "Header", fontSize = 32.sp)
        }
    }
    items(
        count = lazyPagingItems.itemCount,
        key = lazyPagingItems.itemKey { it },
        contentType = lazyPagingItems.itemContentType { "MyPagingItems" },
    ) { index ->
        val item = lazyPagingItems[index]
        PagingItem(item = item)
    }
}

Parameters
contentType: ((item) -> Any?)? = null	a factory of the content types for the item. The item compositions of the same type could be reused more efficiently. Note that null is a valid type and items of such type will be considered compatible.

LazyPagingItems.itemKey

Cmn

Artifact: androidx.paging:paging-compose

View Source

fun <T : Any> LazyPagingItems<T>.itemKey(key: ((item) -> Any)? = null): (index: Int) -> Any

Returns a factory of stable and unique keys representing the item.

Keys are generated with the key lambda that is passed in. If null is passed in, keys will default to a placeholder key. If PagingConfig.enablePlaceholders is true, LazyPagingItems may return null items. Null items will also automatically default to a placeholder key.

This factory can be applied to Lazy foundations such as compose foundation's LazyGridScope or Pagers. Examples:

import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.foundation.pager.HorizontalPager
import androidx.compose.foundation.pager.PageSize
import androidx.compose.foundation.pager.rememberPagerState
import androidx.compose.ui.Modifier
import androidx.compose.ui.unit.dp
import androidx.paging.Pager
import androidx.paging.compose.collectAsLazyPagingItems
import androidx.paging.compose.itemKey

val lazyPagingItems = pager.collectAsLazyPagingItems()
val pagerState = rememberPagerState { lazyPagingItems.itemCount }

HorizontalPager(
    modifier = Modifier.fillMaxSize(),
    state = pagerState,
    pageSize = PageSize.Fixed(200.dp),
    key = lazyPagingItems.itemKey { it },
) { index ->
    val item = lazyPagingItems[index]
    PagingItem(item = item)
}

import androidx.compose.foundation.lazy.grid.GridCells
import androidx.compose.foundation.lazy.grid.LazyVerticalGrid
import androidx.paging.compose.collectAsLazyPagingItems
import androidx.paging.compose.itemContentType
import androidx.paging.compose.itemKey

val lazyPagingItems = pager.collectAsLazyPagingItems()

LazyVerticalGrid(columns = GridCells.Fixed(2)) {
    items(
        count = lazyPagingItems.itemCount,
        key = lazyPagingItems.itemKey { it },
        contentType = lazyPagingItems.itemContentType { "MyPagingItems" },
    ) { index ->
        val item = lazyPagingItems[index]
        PagingItem(item = item)
    }
}

Parameters
key: ((item) -> Any)? = null	a factory of stable and unique keys representing the item. Using the same key for multiple items in the list is not allowed. Type of the key should be saveable via Bundle on Android. When you specify the key the scroll position will be maintained based on the key, which means if you add/remove items before the current visible item the item with the given key will be kept as the first visible one.