PagingDataTransforms

Added in 3.0.0

public final class PagingDataTransforms

Summary

Public methods
static final @NonNull PagingData<@NonNull T>
<T extends Object> filter(
    @NonNull PagingData<@NonNull T> receiver,
    @NonNull Executor executor,
    @NonNull Function1<@NonNull T, @NonNull Boolean> predicate
)

Returns a PagingData containing only elements matching the given predicate.
static final @NonNull PagingData<@NonNull R>
<T extends Object, R extends Object> flatMap(
    @NonNull PagingData<@NonNull T> receiver,
    @NonNull Executor executor,
    @NonNull Function1<@NonNull T, @NonNull Iterable<@NonNull R>> transform
)

Returns a PagingData of all elements returned from applying the given transform to each element, as it is loaded.
static final @NonNull PagingData<@NonNull T>
<T extends Object> insertFooterItem(
    @NonNull PagingData<@NonNull T> receiver,
    @NonNull TerminalSeparatorType terminalSeparatorType,
    @NonNull T item
)

Returns a PagingData containing each original element, with the passed footer item added to the end of the list.
static final @NonNull PagingData<@NonNull T>
<T extends Object> insertHeaderItem(
    @NonNull PagingData<@NonNull T> receiver,
    @NonNull TerminalSeparatorType terminalSeparatorType,
    @NonNull T item
)

Returns a PagingData containing each original element, with the passed header item added to the start of the list.
static final @NonNull PagingData<@NonNull R>
<R extends Object, T extends R> insertSeparators(
    @NonNull PagingData<@NonNull T> receiver,
    @NonNull TerminalSeparatorType terminalSeparatorType,
    @NonNull Executor executor,
    @NonNull Function2<T, T, R> generator
)

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> map(
    @NonNull PagingData<@NonNull T> receiver,
    @NonNull Executor executor,
    @NonNull Function1<@NonNull T, @NonNull R> transform
)

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

Public methods

filter

public static final @NonNull PagingData<@NonNull T> <T extends Object> filter(
    @NonNull PagingData<@NonNull T> receiver,
    @NonNull Executor executor,
    @NonNull Function1<@NonNull T, @NonNull Boolean> predicate
)

Returns a PagingData containing only elements matching the given predicate.

See also
filter

flatMap

public static final @NonNull PagingData<@NonNull R> <T extends Object, R extends Object> flatMap(
    @NonNull PagingData<@NonNull T> receiver,
    @NonNull Executor executor,
    @NonNull Function1<@NonNull T, @NonNull Iterable<@NonNull R>> transform
)

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

See also
flatMap

insertFooterItem

public static final @NonNull PagingData<@NonNull T> <T extends Object> insertFooterItem(
    @NonNull PagingData<@NonNull T> receiver,
    @NonNull TerminalSeparatorType terminalSeparatorType,
    @NonNull T item
)

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
@NonNull TerminalSeparatorType terminalSeparatorType

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

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

insertHeaderItem

public static final @NonNull PagingData<@NonNull T> <T extends Object> insertHeaderItem(
    @NonNull PagingData<@NonNull T> receiver,
    @NonNull TerminalSeparatorType terminalSeparatorType,
    @NonNull T item
)

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
@NonNull TerminalSeparatorType terminalSeparatorType

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

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

insertSeparators

public static final @NonNull PagingData<@NonNull R> <R extends Object, T extends R> insertSeparators(
    @NonNull PagingData<@NonNull T> receiver,
    @NonNull TerminalSeparatorType terminalSeparatorType,
    @NonNull Executor executor,
    @NonNull Function2<T, T, R> generator
)

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
@NonNull TerminalSeparatorType terminalSeparatorType

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

Executor to run the generator function in.
@NonNull Function2<T, T, R> generator

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

public static final @NonNull PagingData<@NonNull R> <T extends Object, R extends Object> map(
    @NonNull PagingData<@NonNull T> receiver,
    @NonNull Executor executor,
    @NonNull Function1<@NonNull T, @NonNull R> transform
)

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

See also
map