PagingDataFutures

public final class PagingDataFutures

Summary

Public methods
static final @NonNull PagingData<@NonNull T>
<T extends Object> PagingDataFutures.filter(
    @NonNull PagingData<@NonNull T> receiver,
    @NonNull AsyncFunction<@NonNull T, @NonNull Boolean> predicate,
    @NonNull Executor executor
)

Returns a PagingData containing only elements matching the given predicate.
static final @NonNull PagingData<@NonNull R>
<T extends Object, R extends Object> PagingDataFutures.flatMap(
    @NonNull PagingData<@NonNull T> receiver,
    @NonNull AsyncFunction<@NonNull T, @NonNull Iterable<@NonNull R>> transform,
    @NonNull Executor executor
)

Returns a PagingData of all elements returned from applying the given transform to each element, as it is loaded.
static final @NonNull PagingData<@NonNull R>
<T extends R, R extends Object> PagingDataFutures.insertSeparators(
    @NonNull PagingData<@NonNull T> receiver,
    @NonNull AsyncFunction<@NonNull AdjacentItems<@NonNull T>, @NonNull R> generator,
    @NonNull 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).
static final @NonNull PagingData<@NonNull R>
<T extends Object, R extends Object> PagingDataFutures.map(
    @NonNull PagingData<@NonNull T> receiver,
    @NonNull AsyncFunction<@NonNull T, @NonNull R> transform,
    @NonNull Executor executor
)

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

Public methods

PagingDataFutures.filter

@NonNull
public static final PagingData<@NonNull T> <T extends Object> PagingDataFutures.filter(
    @NonNull PagingData<@NonNull T> receiver,
    @NonNull AsyncFunction<@NonNull T, @NonNull Boolean> predicate,
    @NonNull Executor executor
)

Returns a PagingData containing only elements matching the given predicate.

Parameters
@NonNull AsyncFunction<@NonNull T, @NonNull Boolean> predicate

AsyncFunction returning false for unmatched items which should be filtered.
@NonNull Executor executor

Executor to run the AsyncFunction in.

PagingDataFutures.flatMap

@NonNull
public static final PagingData<@NonNull R> <T extends Object, R extends Object> PagingDataFutures.flatMap(
    @NonNull PagingData<@NonNull T> receiver,
    @NonNull AsyncFunction<@NonNull T, @NonNull Iterable<@NonNull R>> transform,
    @NonNull Executor executor
)

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

Parameters
@NonNull AsyncFunction<@NonNull T, @NonNull Iterable<@NonNull R>> transform

AsyncFunction to transform an item of type T a list of items of type R.
@NonNull Executor executor

Executor to run the AsyncFunction in.

PagingDataFutures.insertSeparators

@NonNull
public static final PagingData<@NonNull R> <T extends R, R extends Object> PagingDataFutures.insertSeparators(
    @NonNull PagingData<@NonNull T> receiver,
    @NonNull AsyncFunction<@NonNull AdjacentItems<@NonNull T>, @NonNull R> generator,
    @NonNull 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).

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().t