PagingDataFutures

class PagingDataFutures


Summary

Public functions

PagingData<T>
<T : Any> PagingData<T>.filter(
    predicate: AsyncFunction<T, Boolean>,
    executor: Executor
)

Returns a PagingData containing only elements matching the given predicate.

PagingData<R>
<T : Any, R : Any> PagingData<T>.flatMap(
    transform: AsyncFunction<T, Iterable<R>>,
    executor: Executor
)

Returns a PagingData of all elements returned from applying the given transform to each element, as it is loaded.

PagingData<R>
<T : R, R : Any> PagingData<T>.insertSeparators(
    generator: AsyncFunction<AdjacentItems<T>, R?>,
    executor: Executor
)

Returns a PagingData containing each original element, with an optional separator generated by generator, given the elements before and after (or null, in boundary conditions).

PagingData<R>
<T : Any, R : Any> PagingData<T>.map(
    transform: AsyncFunction<T, R>,
    executor: Executor
)

Returns a PagingData containing the result of applying the given transform to each element, as it is loaded.

Public functions

filter

fun <T : Any> PagingData<T>.filter(
    predicate: AsyncFunction<T, Boolean>,
    executor: Executor
): PagingData<T>

Returns a PagingData containing only elements matching the given predicate.

Parameters
predicate: AsyncFunction<T, Boolean>

AsyncFunction returning false for unmatched items which should be filtered.

executor: Executor

Executor to run the AsyncFunction in.

flatMap

fun <T : Any, R : Any> PagingData<T>.flatMap(
    transform: AsyncFunction<T, Iterable<R>>,
    executor: Executor
): PagingData<R>

Returns a PagingData of all elements returned from applying the given transform to each element, as it is loaded.

Parameters
transform: AsyncFunction<T, Iterable<R>>

AsyncFunction to transform an item of type T a list of items of type R.

executor: Executor

Executor to run the AsyncFunction in.

insertSeparators

fun <T : R, R : Any> PagingData<T>.insertSeparators(
    generator: AsyncFunction<AdjacentItems<T>, R?>,
    executor: Executor
): PagingData<R>

Returns a PagingData containing each original element, with an optional separator generated by generator, given the elements before and after (or null, in boundary conditions).

Note that this transform is applied asynchronously, as pages are loaded. Potential separators between pages are only computed once both pages are loaded.

import androidx.paging.insertSeparatorsAsync
import androidx.paging.rxjava2.insertSeparatorsAsync

/*
 * Create letter separators in an alphabetically sorted list.
 *
 * For example, if the input is:
 *     "apple", "apricot", "banana", "carrot"
 *
 * The operator would output:
 *     "A", "apple", "apricot", "B", "banana", "C", "carrot"
 */
pagingDataStream.map { pagingData ->
    // map outer stream, so we can perform transformations on each paging generation
    pagingData.insertSeparatorsAsync(
        AsyncFunction<AdjacentItems<String>, String?> {
            Futures.submit(
                Callable<String?> {
                    val (before, after) = it!!
                    if (after != null && before?.first() != after.first()) {
                        // separator - after is first item that starts with its first letter
                        after.first().uppercaseChar().toString()
                    } else {
                        // no separator - either end of list, or first letters of before/after are the same
                        null
                    }
                },
                executor
            )
        },
        executor
    )
}
import androidx.paging.insertSeparatorsAsync
import androidx.paging.map
import androidx.paging.rxjava2.insertSeparatorsAsync

open class UiModel
data class ItemUiModel(val item: Item) : UiModel()
data class SeparatorUiModel(val char: Char) : UiModel()

/*
 * Create letter separators in an alphabetically sorted list of Items, with UiModel objects.
 *
 * For example, if the input is (each an `Item`):
 *     "apple", "apricot", "banana", "carrot"
 *
 * The operator would output a list of UiModels corresponding to:
 *     "A", "apple", "apricot", "B", "banana", "C", "carrot"
 */
pagingDataStream.map { pagingData ->
    // map outer stream, so we can perform transformations on each paging generation
    pagingData
        .map { item ->
            ItemUiModel(item) // convert items in stream to ItemUiModel
        }
        .insertSeparatorsAsync(
            AsyncFunction<AdjacentItems<ItemUiModel>, UiModel?> {
                Futures.submit(
                    Callable<UiModel> {
                        val (before, after) = it!!
                        if (after != null &&
                            before?.item?.label?.first() != after.item.label.first()
                        ) {
                            // separator - after is first item that starts with its first letter
                            SeparatorUiModel(after.item.label.first().uppercaseChar())
                        } else {
                            // no separator - either end of list, or first letters of before/after are the same
                            null
                        }
                    },
                    executor
                )
            },
            executor
        )
}
Parameters
generator: AsyncFunction<AdjacentItems<T>, R?>

AsyncFunction used to generate separator between two AdjacentItems or the header or footer if either AdjacentItems.before or AdjacentItems.after is null.

executor: Executor

Executor to run the AsyncFunction in.

map

fun <T : Any, R : Any> PagingData<T>.map(
    transform: AsyncFunction<T, R>,
    executor: Executor
): PagingData<R>

Returns a PagingData containing the result of applying the given transform to each element, as it is loaded.

Parameters
transform: AsyncFunction<T, R>

AsyncFunction to transform an item of type T to R.

executor: Executor

Executor to run the AsyncFunction in.