PagingData

Container for Paged data from a single generation of loads.

Each refresh of data (generally either pushed by local storage, or pulled from the network) will have a separate corresponding PagingData.

Summary

Public companion functions
PagingData<T>
<T : Any> empty()

Create a PagingData that immediately displays an empty list of items when submitted to a presenter.
Cmn
PagingData<T>
<T : Any> empty(sourceLoadStates: LoadStates, mediatorLoadStates: LoadStates?)

Create a PagingData that immediately displays an empty list of items when submitted to a presenter.
Cmn
PagingData<T>
<T : Any> from(data: List<T>)

Create a PagingData that immediately displays a static list of items when submitted to a presenter.
Cmn
PagingData<T>
<T : Any> from(
    data: List<T>,
    sourceLoadStates: LoadStates,
    mediatorLoadStates: LoadStates?
)

Create a PagingData that immediately displays a static list of items when submitted to a presenter.
Cmn

Extension functions
PagingData<T>
<T : Any> PagingData<T>.filterAsync(
    predicate: AsyncFunction<T, Boolean>,
    executor: Executor
)

Returns a PagingData containing only elements matching the given predicate.
android
PagingData<R>
<T : Any, R : Any> PagingData<T>.flatMapAsync(
    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.
android
PagingData<R>
<T : R, R : Any> PagingData<T>.insertSeparatorsAsync(
    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).
android
PagingData<R>
<T : Any, R : Any> PagingData<T>.mapAsync(
    transform: AsyncFunction<T, R>,
    executor: Executor
)

Returns a PagingData containing the result of applying the given transform to each element, as it is loaded.
android
PagingData<T>
<T : Any> PagingData<T>.filter(predicate: suspend (T) -> Boolean)

Returns a PagingData containing only elements matching the given predicate
Cmn
PagingData<T>
<T : Any> PagingData<T>.filter(executor: Executor, predicate: (T) -> Boolean)

Returns a PagingData containing only elements matching the given predicate.
android
PagingData<R>
<T : Any, R : Any> PagingData<T>.flatMap(transform: suspend (T) -> Iterable<R>)

Returns a PagingData of all elements returned from applying the given transform to each element, as it is loaded.
Cmn
PagingData<R>
<T : Any, R : Any> PagingData<T>.flatMap(
    executor: Executor,
    transform: (T) -> Iterable<R>
)

Returns a PagingData of all elements returned from applying the given transform to each element, as it is loaded.
android
PagingData<T>
<T : Any> PagingData<T>.insertFooterItem(
    terminalSeparatorType: TerminalSeparatorType,
    item: T
)

Returns a PagingData containing each original element, with the passed footer item added to the end of the list.
Cmn
PagingData<T>
<T : Any> PagingData<T>.insertHeaderItem(
    terminalSeparatorType: TerminalSeparatorType,
    item: T
)

Returns a PagingData containing each original element, with the passed header item added to the start of the list.
Cmn
PagingData<R>
<T : R, R : Any> PagingData<T>.insertSeparators(
    terminalSeparatorType: TerminalSeparatorType,
    generator: suspend (T?, T?) -> 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).
Cmn
PagingData<R>
<R : Any, T : R> PagingData<T>.insertSeparators(
    terminalSeparatorType: TerminalSeparatorType,
    executor: Executor,
    generator: (T?, T?) -> 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).
android
PagingData<R>
<T : Any, R : Any> PagingData<T>.map(transform: suspend (T) -> R)

Returns a PagingData containing the result of applying the given transform to each element, as it is loaded.
Cmn
PagingData<R>
<T : Any, R : Any> PagingData<T>.map(executor: Executor, transform: (T) -> R)

Returns a PagingData containing the result of applying the given transform to each element, as it is loaded.
android
PagingData<T>
<T : Any> PagingData<T>.filterAsync(predicate: (T) -> Single<Boolean>)

Returns a PagingData containing only elements matching the given predicate.
android
PagingData<T>
<T : Any> PagingData<T>.filterAsync(predicate: (T) -> Single<Boolean>)

Returns a PagingData containing only elements matching the given predicate.
android
PagingData<R>
<T : Any, R : Any> PagingData<T>.flatMapAsync(
    transform: (T) -> Single<Iterable<R>>
)

Returns a PagingData of all elements returned from applying the given transform to each element, as it is loaded.
android
PagingData<R>
<T : Any, R : Any> PagingData<T>.flatMapAsync(
    transform: (T) -> Single<Iterable<R>>
)

Returns a PagingData of all elements returned from applying the given transform to each element, as it is loaded.
android
PagingData<R>
<T : R, R : Any> PagingData<T>.insertSeparatorsAsync(
    generator: (T?, T?) -> Maybe<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).
android
PagingData<R>
<T : R, R : Any> PagingData<T>.insertSeparatorsAsync(
    generator: (T?, T?) -> Maybe<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).
android
PagingData<R>
<T : Any, R : Any> PagingData<T>.mapAsync(transform: (T) -> Single<R>)

Returns a PagingData containing the result of applying the given transform to each element, as it is loaded.
android
PagingData<R>
<T : Any, R : Any> PagingData<T>.mapAsync(transform: (T) -> Single<R>)

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

Public companion functions

empty

Cmn
Added in 3.0.0
fun <T : Any> empty(): PagingData<T>

Create a PagingData that immediately displays an empty list of items when submitted to a presenter. E.g., androidx.paging.AsyncPagingDataAdapter and dispatches LoadState.NotLoading on all LoadStates to the presenter.

empty

Cmn
Added in 3.2.0
fun <T : Any> empty(
    sourceLoadStates: LoadStates,
    mediatorLoadStates: LoadStates? = null
): PagingData<T>

Create a PagingData that immediately displays an empty list of items when submitted to a presenter. E.g., androidx.paging.AsyncPagingDataAdapter.

Parameters
sourceLoadStates: LoadStates

LoadStates of PagingSource to pass forward to a presenter. E.g., androidx.paging.AsyncPagingDataAdapter.
mediatorLoadStates: LoadStates? = null

LoadStates of RemoteMediator to pass forward to a presenter. E.g., androidx.paging.AsyncPagingDataAdapter.

from

Cmn 
fun <T : Any> from(data: List<T>): PagingData<T>

Create a PagingData that immediately displays a static list of items when submitted to a presenter. E.g., androidx.paging.AsyncPagingDataAdapter and dispatches LoadState.NotLoading on all LoadStates to the presenter.

Parameters
data: List<T>

Static list of T to display.

from

Cmn 
fun <T : Any> from(
    data: List<T>,
    sourceLoadStates: LoadStates,
    mediatorLoadStates: LoadStates? = null
): PagingData<T>

Create a PagingData that immediately displays a static list of items when submitted to a presenter. E.g., androidx.paging.AsyncPagingDataAdapter.

Parameters
data: List<T>

Static list of T to display.
sourceLoadStates: LoadStates

LoadStates of PagingSource to pass forward to a presenter. E.g., androidx.paging.AsyncPagingDataAdapter.
mediatorLoadStates: LoadStates? = null

LoadStates of RemoteMediator to pass forward to a presenter. E.g., androidx.paging.AsyncPagingDataAdapter.

Extension functions

filterAsync

android 
fun <T : Any> PagingData<T>.filterAsync(
    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.

flatMapAsync

android 
fun <T : Any, R : Any> PagingData<T>.flatMapAsync(
    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.

insertSeparatorsAsync

android 
fun <T : R, R : Any> PagingData<T>.insertSeparatorsAsync(
    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.AdjacentItems
import androidx.paging.insertSeparators
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.AdjacentItems
import androidx.paging.insertSeparators
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.

mapAsync

android 
fun <T : Any, R : Any> PagingData<T>.mapAsync(
    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.

filter

Cmn 
fun <T : Any> PagingData<T>.filter(predicate: suspend (T) -> Boolean): PagingData<T>

Returns a PagingData containing only elements matching the given predicate

filter

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

Returns a PagingData containing only elements matching the given predicate.

See also
filter

flatMap

Cmn 
fun <T : Any, R : Any> PagingData<T>.flatMap(transform: suspend (T) -> Iterable<R>): PagingData<R>

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

flatMap

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

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

See also
flatMap

insertFooterItem

Cmn 
fun <T : Any> PagingData<T>.insertFooterItem(
    terminalSeparatorType: TerminalSeparatorType = FULLY_COMPLETE,
    item: T
): PagingData<T>

Returns a PagingData containing each original element, with the passed footer item added to the end of the list.

The footer item is added to a loaded page which marks the end of the data stream in the LoadType.APPEND direction, either by returning null in PagingSource.LoadResult.Page.nextKey. It will be removed if the last page in the list is dropped, which can happen in the case of loaded pages exceeding PagingConfig.maxSize.

Note: This operation is not idempotent, calling it multiple times will continually add more footers to the end of the list, which can be useful if multiple footer items are required.

Parameters
terminalSeparatorType: TerminalSeparatorType = FULLY_COMPLETE

TerminalSeparatorType used to configure when the header and footer are added.
item: T

The footer to add to the end of the list once it is fully loaded in the LoadType.APPEND direction.
See also
insertHeaderItem

insertHeaderItem

Cmn 
fun <T : Any> PagingData<T>.insertHeaderItem(
    terminalSeparatorType: TerminalSeparatorType = FULLY_COMPLETE,
    item: T
): PagingData<T>

Returns a PagingData containing each original element, with the passed header item added to the start of the list.

The header item is added to a loaded page which marks the end of the data stream in the LoadType.PREPEND direction by returning null in PagingSource.LoadResult.Page.prevKey. It will be removed if the first page in the list is dropped, which can happen in the case of loaded pages exceeding PagingConfig.maxSize.

Note: This operation is not idempotent, calling it multiple times will continually add more headers to the start of the list, which can be useful if multiple header items are required.

Parameters
terminalSeparatorType: TerminalSeparatorType = FULLY_COMPLETE

TerminalSeparatorType used to configure when the header and footer are added.
item: T

The header to add to the front of the list once it is fully loaded in the LoadType.PREPEND direction.
See also
insertFooterItem

insertSeparators

Cmn 
fun <T : R, R : Any> PagingData<T>.insertSeparators(
    terminalSeparatorType: TerminalSeparatorType = FULLY_COMPLETE,
    generator: suspend (T?, T?) -> R?
): 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.insertSeparators

/*
 * 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.insertSeparators { before: String?, after: String? ->
        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
        }
    }
}
 
import androidx.paging.insertSeparators
import androidx.paging.map

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
        }
        .insertSeparators<ItemUiModel, UiModel> { before: ItemUiModel?, after: ItemUiModel? ->
            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
            }
        }
}
Parameters
terminalSeparatorType: TerminalSeparatorType = FULLY_COMPLETE

TerminalSeparatorType used to configure when the header and footer are added.
generator: suspend (T?, T?) -> R?

Generator function used to construct a separator item given the item before and the item after. For terminal separators (header and footer), the arguments passed to the generator, before and after, will be null respectively. In cases where the fully paginated list is empty, a single separator will be added where both before and after items are null.

insertSeparators

android 
fun <R : Any, T : R> PagingData<T>.insertSeparators(
    terminalSeparatorType: TerminalSeparatorType = TerminalSeparatorType.FULLY_COMPLETE,
    executor: Executor,
    generator: (T?, T?) -> R?
): 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.

Kotlin callers should instead use the suspending extension function variant of insertSeparators

/*
 * 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
        PagingDataTransforms.insertSeparators(pagingData, bgExecutor,
                (@Nullable String before, @Nullable String after) -> {
                    if (after != null && (before == null
                            || before.charAt(0) != after.charAt(0))) {
                        // separator - after is first item that starts with its first
                        // letter
                        return Character.toString(
                                Character.toUpperCase(after.charAt(0)));
                    } else {
                        // no separator - either end of list, or first
                        // letters of items are the same
                        return null;
                    }
                }));

/*
 * 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(itemPagingData -> {
    // map outer stream, so we can perform transformations on each paging generation

    // first convert items in stream to UiModel.Item
    PagingData<UiModel.ItemModel> itemModelPagingData = PagingDataTransforms.map(
            itemPagingData, bgExecutor, UiModel.ItemModel::new);

    // Now insert UiModel.Separators, which makes the PagingData of generic type UiModel
    return PagingDataTransforms.insertSeparators(
            itemModelPagingData, bgExecutor,
            (@Nullable UiModel.ItemModel before, @Nullable UiModel.ItemModel after) -> {
                if (after != null && (before == null
                        || before.item.label.charAt(0) != after.item.label.charAt(0))) {
                    // separator - after is first item that starts with its first letter
                    return new UiModel.SeparatorModel(
                            Character.toUpperCase(after.item.label.charAt(0)));
                } else {
                    // no separator - either end of list, or first
                    // letters of items are the same
                    return null;
                }
            });
});

public class UiModel {
    static class ItemModel extends UiModel {
        public Item item;
        ItemModel(Item item) {
            this.item = item;
        }
    }
    static class SeparatorModel extends UiModel {
        public char character;
        SeparatorModel(char character) {
            this.character = character;
        }
    }
}
Parameters
terminalSeparatorType: TerminalSeparatorType = TerminalSeparatorType.FULLY_COMPLETE

TerminalSeparatorType used to configure when the header and footer are added.
executor: Executor

Executor to run the generator function in.
generator: (T?, T?) -> R?

Generator function used to construct a separator item given the item before and the item after. For terminal separators (header and footer), the arguments passed to the generator, before and after, will be null respectively. In cases where the fully paginated list is empty, a single separator will be added where both before and after items are null.

map

Cmn 
fun <T : Any, R : Any> PagingData<T>.map(transform: suspend (T) -> R): PagingData<R>

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

map

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

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

See also
map

filterAsync

android 
fun <T : Any> PagingData<T>.filterAsync(predicate: (T) -> Single<Boolean>): PagingData<T>

Returns a PagingData containing only elements matching the given predicate.

filterAsync

android 
fun <T : Any> PagingData<T>.filterAsync(predicate: (T) -> Single<Boolean>): PagingData<T>

Returns a PagingData containing only elements matching the given predicate.

flatMapAsync

android 
fun <T : Any, R : Any> PagingData<T>.flatMapAsync(
    transform: (T) -> Single<Iterable<R>>
): PagingData<R>

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

flatMapAsync

android 
fun <T : Any, R : Any> PagingData<T>.flatMapAsync(
    transform: (T) -> Single<Iterable<R>>
): PagingData<R>

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

insertSeparatorsAsync

android 
fun <T : R, R : Any> PagingData<T>.insertSeparatorsAsync(
    generator: (T?, T?) -> Maybe<R>
): 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.insertSeparators
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 { before: String?, after: String? ->
        Maybe.fromCallable<String> {
            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
            }
        }.subscribeOn(Schedulers.computation())
    }
}
 
import androidx.paging.insertSeparators
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 { before: ItemUiModel?, after: ItemUiModel? ->
            Maybe.fromCallable<UiModel> {
                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
                }
            }.subscribeOn(Schedulers.computation())
        }
}

insertSeparatorsAsync

android 
fun <T : R, R : Any> PagingData<T>.insertSeparatorsAsync(
    generator: (T?, T?) -> Maybe<R>
): 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.insertSeparators
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 { before: String?, after: String? ->
        Maybe.fromCallable<String> {
            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
            }
        }.subscribeOn(Schedulers.computation())
    }
}
 
import androidx.paging.insertSeparators
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 { before: ItemUiModel?, after: ItemUiModel? ->
            Maybe.fromCallable<UiModel> {
                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
                }
            }.subscribeOn(Schedulers.computation())
        }
}

mapAsync

android 
fun <T : Any, R : Any> PagingData<T>.mapAsync(transform: (T) -> Single<R>): PagingData<R>

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

mapAsync

android 
fun <T : Any, R : Any> PagingData<T>.mapAsync(transform: (T) -> Single<R>): PagingData<R>

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