ItemKeyedDataSource

Kotlin |Java

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

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

Incremental data loader for paging keyed content, where loaded content uses previously loaded items as input to future loads.

Implement a DataSource using ItemKeyedDataSource if you need to use data from item N - 1 to load item N. This is common, for example, in uniquely sorted database queries where attributes of the item such just before the next query define how to execute it.

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

Summary

Nested classes
abstract	`LoadCallback` Callback for ItemKeyedDataSource 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 paging keyed content, where loaded content uses previously loaded items as input to future loads.

Public methods
abstract Key	`getKey(item: Value)` Return a key associated with the given item.
abstract Unit	`loadAfter(params: ItemKeyedDataSource.LoadParams<Key>, callback: ItemKeyedDataSource.LoadCallback<Value>)` Load list data after the key specified in LoadParams.key.
abstract Unit	`loadBefore(params: ItemKeyedDataSource.LoadParams<Key>, callback: ItemKeyedDataSource.LoadCallback<Value>)` Load list data before the key specified in LoadParams.key.
abstract Unit	`loadInitial(params: ItemKeyedDataSource.LoadInitialParams<Key>, callback: ItemKeyedDataSource.LoadInitialCallback<Value>)` Load initial data.
ItemKeyedDataSource<Key, ToValue>	`map(function: Function<Value, ToValue>)` Applies the given function to each value emitted by the DataSource.
ItemKeyedDataSource<Key, ToValue>	`map(function: (Value) -> ToValue)` Applies the given function to each value emitted by the DataSource.
ItemKeyedDataSource<Key, ToValue>	`mapByPage(function: Function<List<Value>, List<ToValue>>)` Applies the given function to each value emitted by the DataSource.
ItemKeyedDataSource<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>

ItemKeyedDataSource()