PageKeyedDataSource

Added in 2.0.0
Deprecated in 3.0.0
kotlin.Any
   ↳ androidx.paging.DataSource
     ↳ 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.

Parameters
<Key : Any>

Type of data used to query Value types out of the DataSource.
<Value : Any>

Type of items being loaded by the DataSource.

Summary

Nested types
abstract class PageKeyedDataSource.LoadCallback<Key : Any?, Value : Any?>

Callback for loadBefore and loadAfter to return data.
abstract class PageKeyedDataSource.LoadInitialCallback<Key : Any?, Value : Any?>

Callback for loadInitial to return data and, optionally, position/count information.

Holder object for inputs to loadInitial.

Holder object for inputs to loadBefore and loadAfter.

Public constructors
<Key : Any, Value : Any> PageKeyedDataSource()
android

Public functions
abstract Unit
loadAfter(
    params: PageKeyedDataSource.LoadParams<Key>,
    callback: PageKeyedDataSource.LoadCallback<Key, Value>
)

Append page with the key specified by LoadParams.key.
android
abstract Unit
loadBefore(
    params: PageKeyedDataSource.LoadParams<Key>,
    callback: PageKeyedDataSource.LoadCallback<Key, Value>
)

Prepend page with the key specified by LoadParams.key.
android
abstract Unit

Load initial data.
android
final PageKeyedDataSource<Key, ToValue>
<ToValue : Any> map(function: Function<Value, ToValue>)

Applies the given function to each value emitted by the DataSource.
android
final PageKeyedDataSource<Key, ToValue>
<ToValue : Any> map(function: (Value) -> ToValue)

Applies the given function to each value emitted by the DataSource.
android
final PageKeyedDataSource<Key, ToValue>
<ToValue : Any> mapByPage(function: Function<List<Value>, List<ToValue>>)

Applies the given function to each value emitted by the DataSource.
android
final PageKeyedDataSource<Key, ToValue>
<ToValue : Any> mapByPage(function: (List<Value>) -> List<ToValue>)

Applies the given function to each value emitted by the DataSource.
android

Inherited functions
From androidx.paging.DataSource
open Unit

Add a callback to invoke when the DataSource is first invalidated.
android
open Unit

Signal the data source to stop loading, and notify its callback.
android
open Unit

Remove a previously added invalidate callback.
android

Inherited properties
From androidx.paging.DataSource
open Boolean
android

Public constructors

PageKeyedDataSource

android 
<Key : Any, Value : Any> PageKeyedDataSource()
Parameters
<Key : Any>

Type of data used to query Value types out of the DataSource.
<Value : Any>

Type of items being loaded by the DataSource.

Public functions

loadAfter

android
Added in 2.0.0
Deprecated in 3.0.0
abstract fun loadAfter(
    params: PageKeyedDataSource.LoadParams<Key>,
    callback: PageKeyedDataSource.LoadCallback<Key, Value>
): Unit

Append page with the key specified by LoadParams.key.

It's valid to return a different list size than the page size if it's easier, e.g. if your backend defines page sizes. It is generally preferred to increase the number loaded than reduce.

Data may be passed synchronously during the load method, or deferred and called at a later time. Further loads going down will be blocked until the callback is called.

If data cannot be loaded (for example, if the request is invalid, or the data would be stale and inconsistent), it is valid to call invalidate to invalidate the data source, and prevent further loading.

Parameters
params: PageKeyedDataSource.LoadParams<Key>

Parameters for the load, including the key for the new page, and requested load size.
callback: PageKeyedDataSource.LoadCallback<Key, Value>

Callback that receives loaded data.

loadBefore

android
Added in 2.0.0
Deprecated in 3.0.0
abstract fun loadBefore(
    params: PageKeyedDataSource.LoadParams<Key>,
    callback: PageKeyedDataSource.LoadCallback<Key, Value>
): Unit

Prepend page with the key specified by LoadParams.key.

It's valid to return a different list size than the page size if it's easier, e.g. if your backend defines page sizes. It is generally preferred to increase the number loaded than reduce.

Data may be passed synchronously during the load method, or deferred and called at a later time. Further loads going down will be blocked until the callback is called.

If data cannot be loaded (for example, if the request is invalid, or the data would be stale and inconsistent), it is valid to call invalidate to invalidate the data source, and prevent further loading.

Parameters
params: PageKeyedDataSource.LoadParams<Key>

Parameters for the load, including the key for the new page, and requested load size.
callback: PageKeyedDataSource.LoadCallback<Key, Value>

Callback that receives loaded data.

loadInitial

android
Added in 2.0.0
Deprecated in 3.0.0
abstract fun loadInitial(
    params: PageKeyedDataSource.LoadInitialParams<Key>,
    callback: PageKeyedDataSource.LoadInitialCallback<Key, Value>
): Unit

Load initial data.

This method is called first to initialize a PagedList with data. If it's possible to count the items that can be loaded by the DataSource, it's recommended to pass the loaded data to the callback via the three-parameter LoadInitialCallback.onResult. This enables PagedLists presenting data from this source to display placeholders to represent unloaded items.

LoadInitialParams.requestedLoadSize is a hint, not a requirement, so it may be may be altered or ignored.

Parameters
params: PageKeyedDataSource.LoadInitialParams<Key>

Parameters for initial load, including requested load size.
callback: PageKeyedDataSource.LoadInitialCallback<Key, Value>

Callback that receives initial load data.

map

android
Added in 3.3.4
Deprecated in 3.3.4
final fun <ToValue : Any> map(function: Function<Value, ToValue>): PageKeyedDataSource<Key, ToValue>

Applies the given function to each value emitted by the DataSource.

Same as mapByPage, but operates on individual items.

Parameters
<ToValue : Any>

Type of items produced by the new DataSource, from the passed function.
function: Function<Value, ToValue>

Function that runs on each loaded item, returning items of a potentially new type.
Returns
PageKeyedDataSource<Key, ToValue>

A new DataSource, which transforms items using the given function.
See also
mapByPage
map
mapByPage

map

android
Added in 3.0.0
Deprecated in 3.0.0
final fun <ToValue : Any> map(function: (Value) -> ToValue): PageKeyedDataSource<Key, ToValue>

Applies the given function to each value emitted by the DataSource.

An overload of map that accepts a kotlin function type.

Same as mapByPage, but operates on individual items.

Parameters
<ToValue : Any>

Type of items produced by the new DataSource, from the passed function.
function: (Value) -> ToValue

Function that runs on each loaded item, returning items of a potentially new type.
Returns
PageKeyedDataSource<Key, ToValue>

A new DataSource, which transforms items using the given function.
See also
mapByPage
map

mapByPage

android
Added in 3.3.4
Deprecated in 3.3.4
final fun <ToValue : Any> mapByPage(function: Function<List<Value>, List<ToValue>>): PageKeyedDataSource<Key, ToValue>

Applies the given function to each value emitted by the DataSource.

Same as map, but allows for batch conversions.

Parameters
<ToValue : Any>

Type of items produced by the new DataSource, from the passed function.
function: Function<List<Value>, List<ToValue>>

Function that runs on each loaded page, returning items of a potentially new type.
Returns
PageKeyedDataSource<Key, ToValue>

A new DataSource, which transforms items using the given function.
See also
map
map
mapByPage

mapByPage

android 
final fun <ToValue : Any> mapByPage(function: (List<Value>) -> List<ToValue>): PageKeyedDataSource<Key, ToValue>

Applies the given function to each value emitted by the DataSource.

An overload of mapByPage that accepts a kotlin function type.

Same as map, but allows for batch conversions.

Parameters
<ToValue : Any>

Type of items produced by the new DataSource, from the passed function.
function: (List<Value>) -> List<ToValue>

Function that runs on each loaded page, returning items of a potentially new type.
Returns
PageKeyedDataSource<Key, ToValue>

A new DataSource, which transforms items using the given function.
See also
map
map
mapByPage