{% setvar book_path %}/reference/kotlin/androidx/_book.yaml{% endsetvar %} {% include "_shared/_reference-head-tags.html" %}
class PagingDataTransforms
Public functions |
|
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@<ERROR CLASS> PagingData<T> |
<T : Any> PagingData<T>.filter(executor: Executor, predicate: (T) -> Boolean) Returns a |
@<ERROR CLASS> PagingData<R> |
Returns a |
@<ERROR CLASS> PagingData<T> |
<T : Any> PagingData<T>.insertFooterItem( Returns a |
@<ERROR CLASS> PagingData<T> |
<T : Any> PagingData<T>.insertHeaderItem( Returns a |
@<ERROR CLASS> PagingData<R> |
<R : Any, T : R> PagingData<T>.insertSeparators( Returns a |
@<ERROR CLASS> PagingData<R> |
<T : Any, R : Any> PagingData<T>.map(executor: Executor, transform: (T) -> R) Returns a |
@<ERROR CLASS>
fun <T : Any> PagingData<T>.filter(executor: Executor, predicate: (T) -> Boolean): @<ERROR CLASS> PagingData<T>
Returns a PagingData
containing only elements matching the given predicate
.
@<ERROR CLASS>
fun <T : Any, R : Any> PagingData<T>.flatMap(
executor: Executor,
transform: (T) -> Iterable<R>
): @<ERROR CLASS> PagingData<R>
Returns a PagingData
of all elements returned from applying the given transform
to each element, as it is loaded.
@<ERROR CLASS>
fun <T : Any> PagingData<T>.insertFooterItem(
terminalSeparatorType: TerminalSeparatorType = FULLY_COMPLETE,
item: T
): @<ERROR CLASS> 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 | |
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terminalSeparatorType: TerminalSeparatorType = FULLY_COMPLETE |
|
item: T |
The footer to add to the end of the list once it is fully loaded in the |
See also | |
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insertHeaderItem |
@<ERROR CLASS>
fun <T : Any> PagingData<T>.insertHeaderItem(
terminalSeparatorType: TerminalSeparatorType = FULLY_COMPLETE,
item: T
): @<ERROR CLASS> 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 | |
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terminalSeparatorType: TerminalSeparatorType = FULLY_COMPLETE |
|
item: T |
The header to add to the front of the list once it is fully loaded in the |
See also | |
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insertFooterItem |
@<ERROR CLASS>
fun <R : Any, T : R> PagingData<T>.insertSeparators(
terminalSeparatorType: TerminalSeparatorType = FULLY_COMPLETE,
executor: Executor,
generator: (T?, T?) -> R?
): @<ERROR CLASS> 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 | |
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terminalSeparatorType: TerminalSeparatorType = FULLY_COMPLETE |
|
executor: Executor |
|
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, |
@<ERROR CLASS>
fun <T : Any, R : Any> PagingData<T>.map(executor: Executor, transform: (T) -> R): @<ERROR CLASS> PagingData<R>
Returns a PagingData
containing the result of applying the given transform
to each element, as it is loaded.
See also | |
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map |