PagingDataTransforms

class PagingDataTransforms


Summary

Public functions

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

Returns a PagingData containing only elements matching the given predicate.

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.

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.

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.

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).

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.

Public functions

filter

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

Returns a PagingData containing only elements matching the given predicate.

flatMap

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.

insertFooterItem

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 PagedList.Config.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

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 PagedList.Config.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

fun <R : Any, T : R> PagingData<T>.insertSeparators(
    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 = 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

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