PageKeyedDataSource

Kotlin |Java

abstract class PageKeyedDataSource<Key : Any, Value : Any> : DataSource<Key, Value>

kotlin.Any
↳	androidx.paging.DataSource<Key, Value>
	↳	androidx.paging.PageKeyedDataSource

Incremental data loader for page-keyed content, where requests return keys for next/previous pages.

Implement a DataSource using PageKeyedDataSource if you need to use data from page N - 1 to load page N. This is common, for example, in network APIs that include a next/previous link or key with each page load.

The InMemoryByPageRepository in the PagingWithNetworkSample shows how to implement a network PageKeyedDataSource using Retrofit, while handling swipe-to-refresh, network errors, and retry.

Summary

Nested classes
abstract	`LoadCallback` Callback for loadBefore and loadAfter to return data.
abstract	`LoadInitialCallback` Callback for loadInitial to return data and, optionally, position/count information.
open	`LoadInitialParams` Holder object for inputs to loadInitial.
open	`LoadParams` Holder object for inputs to loadBefore and loadAfter.

Public constructors
`<init>()` Incremental data loader for page-keyed content, where requests return keys for next/previous pages.

Public methods
abstract Unit	`loadAfter(params: PageKeyedDataSource.LoadParams<Key>, callback: PageKeyedDataSource.LoadCallback<Key, Value>)` Append page with the key specified by LoadParams.key.
abstract Unit	`loadBefore(params: PageKeyedDataSource.LoadParams<Key>, callback: PageKeyedDataSource.LoadCallback<Key, Value>)` Prepend page with the key specified by LoadParams.key.
abstract Unit	`loadInitial(params: PageKeyedDataSource.LoadInitialParams<Key>, callback: PageKeyedDataSource.LoadInitialCallback<Key, Value>)` Load initial data.
PageKeyedDataSource<Key, ToValue>	`map(function: Function<Value, ToValue>)` Applies the given function to each value emitted by the DataSource.
PageKeyedDataSource<Key, ToValue>	`map(function: (Value) -> ToValue)` Applies the given function to each value emitted by the DataSource.
PageKeyedDataSource<Key, ToValue>	`mapByPage(function: Function<List<Value>, List<ToValue>>)` Applies the given function to each value emitted by the DataSource.
PageKeyedDataSource<Key, ToValue>	`mapByPage(function: (List<Value>) -> List<ToValue>)` Applies the given function to each value emitted by the DataSource.

Inherited functions

From class DataSource

`Unit`	`<no name provided>()` Invalidation callback for DataSource. Used to signal when a DataSource a data source has become invalid, and that a new data source is needed to continue loading data.
`Unit`	`addInvalidatedCallback(onInvalidatedCallback: DataSource.InvalidatedCallback)` Add a callback to invoke when the DataSource is first invalidated. Once invalidated, a data source will not become valid again. A data source will only invoke its callbacks once - the first time invalidate is called, on that thread.
`Unit`	`invalidate()` Signal the data source to stop loading, and notify its callback. If invalidate has already been called, this method does nothing.
`Unit`	`removeInvalidatedCallback(onInvalidatedCallback: DataSource.InvalidatedCallback)` Remove a previously added invalidate callback.

Inherited properties

From class DataSource

Boolean

isInvalid

Public constructors

<init>

PageKeyedDataSource()

Incremental data loader for page-keyed content, where requests return keys for next/previous pages.

The InMemoryByPageRepository in the PagingWithNetworkSample shows how to implement a network PageKeyedDataSource using Retrofit, while handling swipe-to-refresh, network errors, and retry.

Parameters
`Key`	Type of data used to query Value types out of the DataSource.
`Value`	Type of items being loaded by the DataSource.

Public methods

loadAfter

abstract fun