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Paging

The Paging Library makes it easier for you to load data gradually and gracefully within your app's RecyclerView.

This table lists all the artifacts in the androidx.paging group.

Artifact Stable Release Release Candidate Beta Release Alpha Release
paging-* 3.1.1 - - 3.2.0-alpha03
paging-compose - - - 1.0.0-alpha17
This library was last updated on: October 24, 2022

Declaring dependencies

To add a dependency on Paging, you must add the Google Maven repository to your project. Read Google's Maven repository for more information.

Add the dependencies for the artifacts you need in the build.gradle file for your app or module:

Groovy

dependencies {
  def paging_version = "3.1.1"

  implementation "androidx.paging:paging-runtime:$paging_version"

  // alternatively - without Android dependencies for tests
  testImplementation "androidx.paging:paging-common:$paging_version"

  // optional - RxJava2 support
  implementation "androidx.paging:paging-rxjava2:$paging_version"

  // optional - RxJava3 support
  implementation "androidx.paging:paging-rxjava3:$paging_version"

  // optional - Guava ListenableFuture support
  implementation "androidx.paging:paging-guava:$paging_version"

  // optional - Jetpack Compose integration
  implementation "androidx.paging:paging-compose:1.0.0-alpha17"
}

Kotlin

dependencies {
  val paging_version = "3.1.1"

  implementation("androidx.paging:paging-runtime:$paging_version")

  // alternatively - without Android dependencies for tests
  testImplementation("androidx.paging:paging-common:$paging_version")

  // optional - RxJava2 support
  implementation("androidx.paging:paging-rxjava2:$paging_version")

  // optional - RxJava3 support
  implementation("androidx.paging:paging-rxjava3:$paging_version")

  // optional - Guava ListenableFuture support
  implementation("androidx.paging:paging-guava:$paging_version")

  // optional - Jetpack Compose integration
  implementation("androidx.paging:paging-compose:1.0.0-alpha17")
}

For information on using Kotlin extensions, see ktx documentation.

For more information about dependencies, see Add Build Dependencies.

Feedback

Your feedback helps make Jetpack better. Let us know if you discover new issues or have ideas for improving this library. Please take a look at the existing issues in this library before you create a new one. You can add your vote to an existing issue by clicking the star button.

Create a new issue

See the Issue Tracker documentation for more information.

Version 3.2

Version 3.2.0-alpha03

October 24, 2022

androidx.paging:paging-*:3.2.0-alpha03 is released. Version 3.2.0-alpha03 contains these commits.

Paging Testing

This release contains a new artifact: paging-testing. This artifact provides APIs designed around unit testing each layer of your app and its integration with Paging in isolation.

For example, this first release includes a TestPager class that allows you to validate the behavior of your own custom PagingSource implementation independently from the Pager and real UI you would normally need to simulate the end-to-end Paging integration.

TestPager should be considered a fake - a test double that mirrors the real implementation of Pager while providing a simplified API surface for testing a PagingSource. These APIs are suspend APIs and should be run within runTest as outlined in the guide for Testing Kotlin coroutines on Android.

An example of these APIs in use can be found in the room-paging tests, which were refactored to use TestPager.

API Changes

  • Enables convenient iteration over LoadResult.Page.data through LoadResult.Page.iterator(). This indirectly allows the usage of the Kotlin standard library flatten method when given a List<LoadResult.Page> such as with the pages property of PagingState that is passed to the PagingSource.getRefreshKey method. (Ie0718)

Version 3.2.0-alpha02

August 10, 2022

androidx.paging:paging-*:3.2.0-alpha02 is released. Version 3.2.0-alpha02 contains these commits.

New Features

  • Paging now provides logs via the AsyncPagingDataDifferor PagingDataAdapter classes to expose debugging information collected from PagingData.
  • The logs can be enabled via the adb shell command adb shell setprop log.tag.Paging [DEBUG|VERBOSE].(b/235527159)

Bug Fixes

  • Fixed the missing PagingDataDiffer constructor error when using paging-common:3.2.0-alpha01 with runtime paging-runtime:3.1.1 or older.(b/235256201)

Version 3.2.0-alpha01

June 1, 2022

androidx.paging:paging-*:3.2.0-alpha01 is released. Version 3.2.0-alpha01 contains these commits.

API Changes

  • Added constructors for PagingDataAdapter and AsyncPagingDataDiffer which accept CoroutineContext instead of CoroutineDispatcher. (Idc878)
  • By default, PagingData.from() and PagingData.empty() will no longer affect CombinedLoadStates on the presenter side. A new overload that allows passing sourceLoadStates and remoteLoadStates in to these constructors has been added to maintain the existing behavior of setting LoadStates to be fully terminal (i.e., NotLoading(endOfPaginationReached = false)), with the option to include remote states as well if needed. If LoadStates are not passed, then the previous CombinedLoadStates will be maintained on the presenter side when it receives the static PagingData. (Ic3ce5, b/205344028)

Bug Fixes

  • The result of PagingSource.getRefreshKey() is now correctly priotized over initialKey in cases where it would return null, but a non-null initialKey was set. (Ic9542, b/230391606)

External Contribution

  • Updated :compose:ui:ui-test api (updateApi) due to test-coroutines-lib migration (I3366d)

Version 3.1

Version 3.1.1

March 9, 2022

androidx.paging:paging-*:3.1.1 is released. Version 3.1.1 contains these commits.

Bug Fixes

  • Removed intermediate LoadState.NotLoading events between generations that were incorrectly inserted by .cachedIn(). This change makes it much easier to react on LoadState changes by removing redundant LoadState.NotLoading events that were produced between retrying failed loads, when refreshing or during invalidation.

Version 3.1.0

November 17, 2021

androidx.paging:paging-*:3.1.0 is released. Version 3.1.0 contains these commits.

Important changes since 3.0.0

  • Flow<PagingData>.observable and Flow<PagingData>.flowable APIs are no longer experimental
  • Behavior changes to LoadState:
    • endOfPaginationReached is now always false for LoadType.REFRESH for both PagingSource and RemoteMediator
    • LoadStates from Paging now await valid values from both PagingSource and RemoteMediator before emitting downstream. New generations of PagingData will now always correctly begin with Loading for refresh state instead of resetting to NotLoading incorrectly in some cases.
    • .loadStateFlow and .addLoadStateListener on presenter APIs no longer redundantly send an initial CombinedLoadStates that always has mediator states set to null
  • Cancellation on past generations now happens eagerly on invalidation / new generations. It should no longer be required to use .collectLatest on Flow<PagingData>, although it is still recommended to do so.
  • PagingSource.LoadResult.Invalid has been added as a new return type from PagingSource.load, which causes Paging to discard any pending or future load requests to this PagingSource and invalidate it. This return type is designed to handle potentially invalid or stale data that can be returned from the database or network.
  • Added .onPagesPresented and .addOnPagesUpdatedListener presenter APIs which triggered synchronously as pages are presented in UI. Page updates can happen in the following scenarios:
    • Initial load of a new generation of PagingData completes, regardless if the new generation contains any changes to the presented items. i.e., A new generation completing initial load with no updates because the list is exactly the same will still trigger this callback.
    • A page is inserted, even if the inserted page contains no new items.
    • A page is dropped, even if the dropped page was empty.

Version 3.1.0-rc01

November 3, 2021

androidx.paging:paging-*:3.1.0-rc01 is released. Version 3.1.0-rc01 contains these commits.

Bug Fixes

  • Fixed a race condition + memory leak in .cachedIn() in cases where multiple load events were sent by Paging downstream while there are no observers or between when an observer is switching to a new PagingData. (Ib682e)

Version 3.1.0-beta01

October 13, 2021

androidx.paging:paging-*:3.1.0-beta01 is released. Version 3.1.0-beta01 contains these commits.

Bug Fixes

  • Fixed an issue where many rapid item accesses could cause them to get dropped for consideration in prefetchDistance, causing page loads to stall. This is especially an issue when many items are laid out at once in an order which would prioritize loading against the user scroll direction. These item accesses are now buffered and synchronously prioritized to prevent them from getting dropped. (aosp/1833273)

Version 3.1.0-alpha04

September 29, 2021

androidx.paging:paging-*:3.1.0-alpha04 is released. Version 3.1.0-alpha04 contains these commits.

API Changes

  • Flow<PagingData>.observable and Flow<PagingData>.flowable APIs are no longer experimental. (Ie0bdd)

Bug Fixes

  • For LoadStates, endOfPaginationReached is now always false for LoadType.REFRESH. Previously, it was possible for endOfPaginationReached to be true for RemoteMediator REFRESH, but not for PagingSource. This behavior is now consolidated to always return false as it never makes sense for REFRESH to be terminal, and is now documented as part of the API contract in LoadStates. When deciding if pagination is terminated, you should always do so with respect to either the APPEND or PREPEND directions. (I047b6)

  • LoadStates from Paging now await valid values from both PagingSource and RemoteMediator before emitting downstream between generations. This prevents new generations of PagingData from sending NotLoading in CombinedLoadStates.source.refresh if it was already Loading; new generations of PagingData will now always correctly begin with Loading for refresh state instead of first resetting to NotLoading incorrectly in some cases.

    Cancellation on past generations now happen eagerly on invalidation / new generations. It should no longer be required to use .collectLatest on Flow<PagingData>, although it is still highly recommended to do so. (I0b2b5, b/177351336, b/195028524)

  • .loadStateFlow and .addLoadStateListener on presenter APIs no longer redundantly send an initial CombinedLoadStates that always has mediator states set to null and source states set to NotLoading(endOfPaginationReached = false). This means that:

    1. mediator states will always be populated if you use RemoteMediator.
    2. Registering a new loadState listener or a new collector on .loadStateFlow will no longer immediately emit the current value if it hasn't received a real CombinedLoadStates from PagingData. This can happen if a collector or listener starts before a PagingData has been submitted. (I1a748)

Version 3.1.0-alpha03

July 21, 2021

androidx.paging:paging-*:3.1.0-alpha03 is released. Version 3.1.0-alpha03 contains these commits.

API Changes

  • A third LoadResult return type LoadResult.Invalid is added to PagingSource. When a PagingSource.load returns LoadResult.Invalid, paging will discard the loaded data and invalidate the PagingSource. This return type is designed to handle potentially invalid or stale data that can be returned from the database or network.

    For example, if the underlying database gets written into but the PagingSource does not invalidate in time, it may return inconsistent results if its implementation depends on the immutability of the backing dataset it loads from (e.g., LIMIT OFFSET style db implementations). In this scenario, it is recommended to check for invalidation after loading and to return LoadResult.Invalid, which causes Paging to discard any pending or future load requests to this PagingSource and invalidate it.

    This return type is also supported by Paging2 API that leverages LivePagedList or RxPagedList. When using a PagingSource with Paging2's PagedList APIs, the PagedList is immediately detached, stopping further attempts to load data on this PagedList and triggers invalidation on the PagingSource.

    LoadResult is a sealed class, which means this is a source-incompatible change such that use cases directly using PagingSource.load results will have to handle LoadResult.Invalid at compile time. For example, Kotlin users leveraging exhaustive-when to check return type will have to add a check for Invalid type. (Id6bd3, b/191806126, b/192013267)

Bug Fixes

  • Invalidation callbacks added via PagingSource.registerInvalidatedCallback or DataSource.addInvalidatedCallback now automatically trigger if they were registered on a PagingSource / DataSource that was already invalid. This resolves a race condition which caused Paging to drop invalidation signals and get stuck when provided a Source which was already invalid during initial load. Additionally, invalidate callbacks are now properly removed after being triggered as they are guaranteed to be called at most once. (I27e69)
  • Submitting the placeholder initial value (InitialPagedList) from a newly instantiated PagedList stream, e.g., LivePagedListBuilder or RxPagedListBuilder will no longer clear previously loaded data.

Version 3.1.0-alpha02

July 1, 2021

androidx.paging:paging-*:3.1.0-alpha02 is released. Version 3.1.0-alpha02 contains these commits.

New Features

  • Added onPagesPresented listener and flow presenter APIs which trigger immediately after presented pages are updated in UI.

    Since these updates are synchronous with UI, you may call adapter methods such as .snapshot, .getItemCount, to inspect the state after the update has been applied. Note that .snapshot() was left to be explicitly called because it can be expensive to do on every update.

    Page updates can happen in the following scenarios:

    • Initial load of a new generation of PagingData completes, regardless if the new generation contains any changes to the presented items. i.e., A new generation completing initial load with no updates because the list is exactly the same will still trigger this callback.
    • A page is inserted, even if the inserted page contains no new items
    • A page is dropped, even if the dropped page was empty (I272c9, b/189999634)

Bug Fixes

  • Accessing PagedList.dataSource from the initial value produced by LivePagedList or RxPagedList will no longer incorrectly throw an IllegalStateException (I96707)

Version 3.1.0-alpha01

June 2, 2021

androidx.paging:paging-*:3.1.0-alpha01 is released. Version 3.1.0-alpha01 contains these commits.

API Changes

  • Classes provided by paging-rxjava3 now live under the androidx.paging.rxjava3 package so that they do not conflict with paging-rxjava2 (Ifa7f6)

Bug Fixes

  • Fixed an issue where Paging would sometimes send no-op differ events to RecyclerView, which could cause certain listeners to trigger early. (Ic507f, b/182510751)

External Contribution

Paging Compose Version 1.0.0

Version 1.0.0-alpha17

October 24, 2022

androidx.paging:paging-compose:1.0.0-alpha17 is released. Version 1.0.0-alpha17 contains these commits.

New Features

Version 1.0.0-alpha16

August 10, 2022

androidx.paging:paging-compose:1.0.0-alpha16 is released. Version 1.0.0-alpha16 contains these commits.

New Features

  • Paging now provides logs via the LazyPagingItems class to expose debugging information collected from PagingData.
  • The logs can be enabled via the adb shell command adb shell setprop log.tag.Paging [DEBUG|VERBOSE]. ([b/235527159}(https://issuetracker.google.com/issues/235527159))

Bug Fixes

  • Fixed the missing PagingDataDiffer constructor error when using paging-compose:1.0.0-alpha15 with paging-common:3.1.1 or older.(b/235256201,b/239868768)

Version 1.0.0-alpha15

June 1, 2022

androidx.paging:paging-compose:1.0.0-alpha15 is released. Version 1.0.0-alpha15 contains these commits.

API Changes

  • Added constructors for PagingDataAdapter and AsyncPagingDataDiffer which accept CoroutineContext instead of CoroutineDispatcher. (Idc878)

Bug Fixes

  • LazyPagingItems now sets the initial loadState to have a LoadState.Loading refresh. (I55043, b/224855902)

Version 1.0.0-alpha14

October 13, 2021

androidx.paging:paging-compose:1.0.0-alpha14 is released. Version 1.0.0-alpha14 contains these commits.

Version 1.0.0-alpha13

September 29, 2021

androidx.paging:paging-compose:1.0.0-alpha13 is released. Version 1.0.0-alpha13 contains these commits.

API Changes

  • LazyPagingItems.snapshot() function was replaced withLazyPagingItems.itemSnapshotList property (Ie2da8)
  • Deprecated LazyPagingItems.getAsState() was removed (Ie65e4)

Version 1.0.0-alpha12

July 21, 2021

androidx.paging:paging-compose:1.0.0-alpha12 is released. Version 1.0.0-alpha12 contains these commits.

API Changes

  • items(lazyPagingItems) and itemsIndexed(lazyPagingItems) used to connect Paging with LazyColumn/Row now accept the option key param which allows you to specify a stable key representing the item. You can read more about keys here. (I7986d)
  • Function lazyPagingItems.getAsState(index) is now deprecated. Use lazyPagingItems[index] instead. (I086cb, b/187339372)

Version 1.0.0-alpha11

June 30, 2021

androidx.paging:paging-compose:1.0.0-alpha11 is released. Version 1.0.0-alpha11 contains these commits.

Version 1.0.0-alpha10

June 2, 2021

androidx.paging:paging-compose:1.0.0-alpha10 is released. Version 1.0.0-alpha10 contains these commits.

Version 1.0.0-alpha09

May 18, 2021

androidx.paging:paging-compose:1.0.0-alpha09 is released. Version 1.0.0-alpha09 contains these commits.

Bug Fixes

  • LazyPagingItems' itemCount and item getter are now observable which allows it to be used with LazyVerticalGrid as well (Ie2446, b/171872064, b/168285687)

Compose Compatibility

  • androidx.paging:paging-compose:1.0.0-alpha09 is only compatible with Compose version 1.0.0-beta07 and above.

Version 1.0.0-alpha08

February 24, 2021

androidx.paging:paging-compose:1.0.0-alpha08 is released. Version 1.0.0-alpha08 contains these commits.

Updated to integrate with Compose 1.0.0-beta01.

Version 1.0.0-alpha07

February 10, 2021

androidx.paging:paging-compose:1.0.0-alpha07 is released. Version 1.0.0-alpha07 contains these commits.

Updated to integrate with Compose alpha12.

Version 1.0.0-alpha06

January 28, 2021

androidx.paging:paging-compose:1.0.0-alpha06 is released. Version 1.0.0-alpha06 contains these commits.

Bug Fixes

Updated to depend on Compose 1.0.0-alpha11.

Version 1.0.0-alpha05

January 13, 2021

androidx.paging:paging-compose:1.0.0-alpha05 is released. Version 1.0.0-alpha05 contains these commits.

Updated to depend on Compose 1.0.0-alpha10.

Version 1.0.0-alpha04

December 16, 2020

androidx.paging:paging-compose:1.0.0-alpha04 is released. Version 1.0.0-alpha04 contains these commits.

Bug Fixes

  • Updated the convenience properties, CombinedLoadStates.refresh, CombinedLoadStates.prepend, CombinedLoadStates.append to only transition from Loading to NotLoading after both mediator and source load states are NotLoading to ensure the remote update has been applied. (I65619)

Version 1.0.0-alpha03

December 2, 2020

androidx.paging:paging-compose:1.0.0-alpha03 is released. Version 1.0.0-alpha03 contains these commits.

  • Updated to match Compose 1.0.0-alpha08.

Version 1.0.0-alpha02

November 11, 2020

androidx.paging:paging-compose:1.0.0-alpha02 is released. Version 1.0.0-alpha02 contains these commits.

API Changes

  • Added .peek(), .snapshot(), .retry() and .refresh() methods to LazyPagingItems which expose the same functionality available in AsyncPagingDataDiffer / PagingDataAdapter (Iddfe8, b/172041660)

Version 1.0.0-alpha01

October 28, 2020

androidx.paging:paging-compose:1.0.0-alpha01 is released. Version 1.0.0-alpha01 contains these commits.

New Features

The paging-compose artifact provides integration between The Paging Library and Jetpack Compose. A simple usage example:

  @Composable
  @OptIn(ExperimentalLazyDsl::class)
  fun ItemsDemo(flow: Flow<PagingData<String>>) {
      val lazyPagingItems = flow.collectAsLazyPagingItems()
      LazyColumn {
          items(lazyPagingItems) {
              Text("Item is $it")
          }
      }
  }

Version 3.0.1

Version 3.0.1

July 21, 2021

androidx.paging:paging-*:3.0.1 is released. Version 3.0.1 contains these commits.

Bug Fixes

  • Accessing PagedList.dataSource from the initial value produced by LivePagedList or RxPagedList will no longer incorrectly throw an IllegalStateException (I96707)

Version 3.0.0

Version 3.0.0

May 5, 2021

androidx.paging:paging-*:3.0.0 is released. Version 3.0.0 contains these commits.

Major features of 3.0.0

The majority of the existing API from Paging 2.x.x has been deprecated in favor of the new Paging 3 APIs to bring the following improvements:

  • First-class support for Kotlin coroutines and Flow
  • Support for cancellation
  • Built-in load state and error signals
  • Retry + refresh functionality
  • All three DataSource subclasses have been combined into a unified PagingSource class
  • Custom page transformations including a built-in one for adding separators
  • Loading state headers and footers

Version 3.0.0-rc01

April 21, 2021

androidx.paging:paging-*:3.0.0-rc01 is released. Version 3.0.0-rc01 contains these commits.

Bug Fixes

  • Fixed an issue where Paging would sometimes send no-op differ events to RecyclerView, which could cause certain listeners to trigger early. (Ic507f, b/182510751)

Version 3.0.0-beta03

March 24, 2021

androidx.paging:paging-*:3.0.0-beta03 is released. Version 3.0.0-beta03 contains these commits.

Bug Fixes

  • We've revamped how placeholders are handled when list is reloaded to prevent unexpected jumps in RecyclerView. See NullPaddedDiffing.md for details. (If1490, b/170027529, b/177338149)
  • The various PagedList builders (old compatibility path) no longer incorrectly synchronously call DataSource.Factory.create() on Main thread when .build() is called. (b/182798948)

Version 3.0.0-beta02

March 10, 2021

androidx.paging:paging-*:3.0.0-beta02 is released. Version 3.0.0-beta02 contains these commits.

API Changes

  • Rx3 extensions now correctly propagate @ExperimentalCoroutinesApi Opt-In requirement. Previously they were marked on the @get method, which is ignored by the Kotlin Compiler due to: https://youtrack.jetbrains.com/issue/KT-45227 (I5733c)

Bug Fixes

  • Enforce restrictions on public usage of experimental APIs (I6aa29, b/174531520)
  • Fixed a bug causing PagingState to always be null when remote refresh is called.
  • Fixed a bug where empty pages returned by PagingSource could prevent Paging from fetching again to fulfill prefetchDistance causing Paging to get “stuck”.

Version 3.0.0-beta01

February 10, 2021

androidx.paging:paging-*:3.0.0-beta01 is released. Version 3.0.0-beta01 contains these commits.

API Changes

  • Rx2 and Rx3 wrappers now expose the experimental annotation it depends on. If you are using the Rx compat wrappers in paging-rxjava2 or paging-rxjava3, you will now need to annotate usages with @OptIn(ExperimentalCoroutinesApi::class) (Ib1f9d)

Bug Fixes

  • Fixed IndexOutOfBoundsException: Inconsistency detected sometimes thrown when using v2 DataSource APIs through compatibility paths
  • isInvalid call during initialization of DataSource when used via compatibility paths are now correctly launched on fetchDispatcher instead of on the main thread. This fixes an IllegalStateException due to Db access on the main thread when using Room’s PagingSource implementation.

Version 3.0.0-alpha13

January 27, 2021

androidx.paging:paging-*:3.0.0-alpha13 is released. Version 3.0.0-alpha13 contains these commits.

API Changes

  • PagingSource.getRefreshKey is no longer optional to implement, it is now an abstract function without a default implementation. Migrating users can either continue returning the default implementation, which simply returns null, but getRefreshKey() should have a real implementation returning a key based on user's current scroll position that allows Paging to continue loading centered around the viewport via PagingState.anchorPosition if possible. (I4339a)
  • InvalidatingPagingSourceFactory is now a final class (Ia3b0a)
  • Allow configuration of terminal separator (header / footer) behavior with an additional optional SeparatorType parameter. The two options are:
    • FULLY_COMPLETE - existing behavior; wait for both PagingSource and RemoteMediator to mark endOfPaginationReached before adding terminal separators. If RemoteMediator is not used, remote loadState is ignored. This is primarily useful if you only want to show section separators when the section is fully loaded, including fetching from remote source e.g., network.
    • SOURCE_COMPLETE - only wait for PagingSource to mark endOfPaginationReached even if RemoteMediator is used. This allows headers and footers to be presented synchronously with the initial load, which prevents users from needing to scroll to see terminal separators. (Ibe993, b/174700218)

Bug Fixes

  • Fixed a rare memory leak which happens when a PagingSource is invalidated before PageFetcher can even begin to start loading from it. (I9606b, b/174625633)

Version 3.0.0-alpha12

January 13, 2021

androidx.paging:paging-*:3.0.0-alpha12 is released. Version 3.0.0-alpha12 contains these commits.

API Changes

  • InvalidatingPagingSourceFactory is no longer an abstract class as it never had any abstract methods. (I4a8c4)
  • Added an overload of .cachedIn() that accepts ViewModel instead of Lifecycle or CoroutineScope for Java users. (I97d81, b/175332619)
  • Allow Java callers to use PagingData transform operations in an async way, by accepting an Executor into transform operator arguments. All of the -Sync transform operators have the -Sync suffix removed now, and Kotlin Coroutine users will need to disambiguate by calling the extension function which accepts a suspending block instead. All PagingData transformation operators have been moved to extensions under the static PagingDataTransforms class. Java users will need to call them via static helpers e.g., PagingDataTransforms.map(pagingData, transform) For Kotlin users, the syntax is the same but you'll need to import the function. (If6885, b/172895919)

Bug Fixes

  • Fixed a bug where RemoteMediator.load() would not be called during adapter.refresh() if the end of pagination had already been reached.

Version 3.0.0-alpha11

December 16, 2020

androidx.paging:paging-*:3.0.0-alpha11 is released. Version 3.0.0-alpha11 contains these commits.

New Features

  • Saved state support added for the following basic use cases (full support, especially in the layered source case is still a work in progress):
    • flow is cached and application is not killed (e.g. flow is cached in a view model and activity is recreated in process)
    • paging source is counted, placeholders are enabled and the layout is not staggered.

API Changes

  • PagingSource.getRefreshKey() is now stable API (I22f6f, b/173530980)
  • PagingSource.invalidate is no longer an open function. If you need to get notified when invalidation happens, consider calling the registerInvalidatedCallback method instead of overriding invalidate. (I628d9, b/173029013, b/137971356)
  • Pager now has a single experimental constructor alongside its regular constructors, rather than leaking experimental APIs into non-experimental public API via the opt-in annotation. (I9dc61, b/174531520)
  • Updated the convenience properties, CombinedLoadStates.refresh, CombinedLoadStates.prepend, CombinedLoadStates.append to only transition from Loading to NotLoading after both mediator and source load states are NotLoading to ensure the remote update has been applied. (I65619)

  • LoadParams.pageSize has been removed (it was already deprecated). The recommendation is to use LoadParams.loadSize in your PagingSource.

    LoadParams.loadSize is always equal to the PagingConfig.pageSize except for the initial load call where it is equal to the PagingConfig.initialLoadSize.

    If you are testing your Paging2 DataSource without using a Pager or PagedList, pageSize may not match the PagingConfig.pageSize if you are also setting initialLoadSize. If it is important for your tests, try using a Pager/PagedList instead which will internally set the correct PageSize for your DataSource load methods. (I98ac7, b/149157296)

Bug Fixes

  • Fixed a crash due to IllegalStateException when using separators with PagingConfig.maxSize set. (I0ed33, b/174787528)
  • Fixed a bug where load state for PREPEND / APPEND would not update to NotLoading(endOfPaginationReached = true) immediately after initial load if RemoteMediator was set (I8cf5a)
  • Fixed a bug where presenter-side APIs such as .snapshot(), .peek(), etc., would return the previous (out-of-date) list within ListUpdateCallback updates.
  • Fixed a bug where Separators operators would not add headers or footers when used with RemoteMediator
  • Fixed a bug where LoadState updates to NotLoading for RemoteMediator would get stuck in the Loading state
  • Fixed a bug where the Paging2.0 compatibility API, .asPagingSourceFactory(), could cause the backing DataSource to be initialized on the incorrect CoroutineDispatcher. This resolves a crash and possible ANR cases, especially when using Room’s current implementation of PagingSource, which uses this compatibility path.

Version 3.0.0-alpha10

December 2, 2020

androidx.paging:paging-*:3.0.0-alpha10 is released. Version 3.0.0-alpha10 contains these commits.

API Changes

  • The deprecated dataRefreshFlow and dataRefreshListener APIs have been removed as they are redundant with loadStateFlow / Listener updates. For those migrating, the loadStateFlow equivalent is:

    loadStateFlow.distinctUntilChangedBy { it.refresh }
    .filter { it.refresh is NotLoading }

    (Ib5570, b/173530908)

Bug Fixes

  • endOfPaginationReached for RemoteMediator REFRESH now correctly propagate to LoadState updates and prevents remote APPEND and PREPEND from triggering. (I94a3f, b/155290248)
  • Presenting an empty list either due to empty initial page or heavy filtering will no longer prevent Paging from kicking off PREPEND or APPEND loads. (I3e702, b/168169730)
  • Fixed an issue where getRefreshKey does not get called on subsequent generations of PagingSource when invalidations occur rapidly. (I45460, b/170027530)

External Contribution

  • A new abstract class InvalidatingPagingSourceFactory has been added with an .invalidate() API that forwards invalidate to all of the PagingSources it emits. Thanks to @claraf3! (Ie71fc, b/160716447)

Known Issues

  • Headers and footers from the .insertSeparators() transform may not appear immediately when using RemoteMediator b/172254056
  • Using RemoteMediator can cause remote LoadState to get stuck if invalidation and PagingSource.load(LoadParams.Refresh(...)) completes before RemoteMediator.load() returns b/173717820

Version 3.0.0-alpha09

November 11, 2020

androidx.paging:paging-*:3.0.0-alpha09 is released. Version 3.0.0-alpha09 contains these commits.

API Changes

  • Fully deprecate dataRefreshFlow / Listener methods with a replaceWith clause. (I6e2dd)

Bug Fixes

  • Fix for IllegalArgumentException being throw when using separators with RemoteMediator and an invalidate is triggered while a remote load that would return endOfPagination is still running (I3a260)

Version 3.0.0-alpha08

October 28, 2020

androidx.paging:paging-*:3.0.0-alpha08 is released. Version 3.0.0-alpha08 contains these commits.

API Changes

  • The Kotlin / Java variants of DataSource.InvalidatedCallback have been combined by enabling SAM-conversions in Kotlin via functional interface (available in Kotlin 1.4). This also fixes a bug where the kotlin variant of invalidate callbacks were not called after transformed by .map or .mapByPage. (I1f244, b/165313046)

Bug Fixes

  • Paging’s interaction with ViewPager has been improved considerably. Specifically, Paging will no longer cancel a RemoteMediator#load call due to a page invalidation. It will also no longer make an append/prepend load request, if REFRESH is required, until REFRESH request completes successfully. (I6390b, b/162252536)
  • API lint check for MissingGetterMatchingBuilder is enabled for androidx (I4bbea, b/138602561)
  • Fixed a bug where .withLoadState* ConcatAdapter helpers would crash due to notifying RecyclerView from background thread (I18bb5, b/170988309)
  • Fixed a bug where loading a very small non-empty page would sometimes prevent prefetch from triggering loads correctly.Iffda3 b/169259468

Version 3.0.0-alpha07

October 1, 2020

androidx.paging:paging-*:3.0.0-alpha07 is released. Version 3.0.0-alpha07 contains these commits.

API Changes

  • Async PagingData Guava-based operators now accept an Executor as a param, to control execution context. (Id4372)

Bug Fixes

  • Fixed IndexOutOfBounds exception thrown in RemoteMediator due to a race condition. (I00b7f, b/165821814)
  • Fixed a race condition in DataSource -> PagingSource conversion that could cause the resulting PagingSource to ignore invalidation signals from DataSource.
  • Fixed an issue in page fetchin logic that would sometimes cause it to fail to pick up new generations of PagingSource until PagingDataAdapter.refresh() was invoked
  • Fixed an issue that would cause scroll-position to sometimes be lost when using a DataSource converted into a PagingSource (such as the one produced by Room), in conjunction with RemoteMediator

External Contribution

  • Thanks to @simonschiller for adding RxJava2, RxJava3, and Guava-based async transformation operators for PagingData!

Version 3.0.0-alpha06

September 2, 2020

androidx.paging:paging-*:3.0.0-alpha06 is released. Version 3.0.0-alpha06 contains these commits.

API Changes

  • UnsupportedOperationException with clearer messaging around lack of support for stable ids is now thrown whenever PagingDataAdapter.setHasStableIds is called. (Ib3890, b/158801427)

Bug Fixes

  • insertSeparators no longer filters out empty pages allowing prefetch distance to be respected by the presenter even in cases where many empty pages are inserted. (I9cff6, b/162538908)

Version 3.0.0-alpha05

August 19, 2020

androidx.paging:paging-*:3.0.0-alpha05 is released. Version 3.0.0-alpha05 contains these commits.

Bug Fixes

  • Paging now correctly prefetches pages even when the presented data is heavily filtered
  • Returning LoadResult.Error to a retried load no longer causes Item accesses to incorrectly re-trigger retry

External Contribution

  • Thanks to Clara F for helping clean up some tests! (549612)

Version 3.0.0-alpha04

August 5, 2020

androidx.paging:paging-*:3.0.0-alpha04 is released. Version 3.0.0-alpha04 contains these commits.

API Changes

  • Added peek() API to AsyncPagingDataDiffer and PagingDataAdapter to allow presented data access without trigger page loads. (I38898, b/159104197)
  • Added a snapshot() API to PagingDataAdapter and AsyncPagingDataDiffer to allow retrieving the presented items without triggering page fetch. (I566b6, b/159104197)
  • Added a PagingData.from(List<T>) constructor to allow presenting static lists, which can be combined with the overall PagingData flow to show static lists in certain states, e.g., before initial REFRESH finishes or simply for testing transformations. (Id134d)
  • Deprecate dataRefresh Flow / Listener APIs as they were intended to expose the presented items state on REFRESH, but with improvements to loadState Flow / Listener callback timing, and itemCount property, it is redundant (Ia19f3)
  • Added RxJava3 compatibility wrappers for PagingSource and RemoteMediator (I49ef3, b/161480176)

Bug Fixes

  • PositionalDataSource converted into PagingSource via toPagingSourceFactory helper, including PagingSource generated by Room now correctly mark themselves to support jumping. (I3e84c, b/162161201)
  • Fixed a bug where using the synchronous variant of submitData would sometimes lead to a race causing a ClosedSendChannelException (I4d702, b/160192222)

External Contribution

  • Thanks to Zac Sweers for adding RxJava3 compatibility wrappers on behalf of Slack! (I49ef3, b/161480176)

Version 3.0.0-alpha03

July 22, 2020

androidx.paging:paging-*:3.0.0-alpha03 is released. Version 3.0.0-alpha03 contains these commits.

API Changes

  • The constructor for PagingState is now public, which should make testing implementations of getRefreshKey() easier (I8bf15)
  • Hid DataSource kotlin map function variants from Java, to resolve ambiguity between original and kotlin variants. (If7b23, b/161150011)
  • Redundant APIs intended as conveniences for Kotlin users have been marked @JvmSynthetic (I56ae5)
  • Added overloads for LoadResult.Page's constructor which defaults itemsBefore and itemsAfter to COUNT_UNDEFINED (I47849)
  • Made existing PagingData operators accept suspending methods and introduced new mapSync, flatMapSync, and filterSync non-suspending operators for Java users. The existing transformation methods have been moved to extension functions so Kotlin users will now need to import them. (I34239, b/159983232)

Bug Fixes

  • Room (and PositionalDataSource) PagingSources will now display a leading separator as part of the first page, so the user doesn't need to scroll to reveal it. (I6f747, b/160257628)
  • Item accesses on placeholders now correctly trigger PagingSource loads until a page is returned that fulfills the requested index after being transformed by PagingData.filter() (I95625, b/158763195)
  • Fix for a bug where sometimes scrolling after PagingSource returns an error could prevent PagingDataAdapter.retry() from retrying. (I1084f, b/160194384)
  • Fixes an issue where item accesses after dropping a page might not load pages although the item access was within prefetchDistance (Ie95ae, b/160038730)
  • Setting PagingConfig.maxSize no longer enables placeholders after a drop event (I2be29, b/159667766)

Version 3.0.0-alpha02

June 24, 2020

androidx.paging:paging-*:3.0.0-alpha02 is released. Version 3.0.0-alpha02 contains these commits.

API Changes

  • Added overloads for PagingConfig's constructor with common default values (I39c50, b/158576040)
  • Added overloads for constructors of PagingDataAdapter and AsyncPagingDataDiffer with common default values (Ie91f5)
  • The adapter APIs, dataRefreshFlow and dataRefreshListener now pass a Boolean to signal whether a PagingData is empty (I6e37e, b/159054196)
  • Added RxJava and Guava APIs for RemoteMediator - RxRemoteMediator and ListenableFutureRemoteMediator
  • Added helpers to PagingState for common item access such as isEmpty() and firstItemOrNull() (I3b5b6, b/158892717)

Bug Fixes

  • Pager now checks for PagingSource reuse in factory, to prevent accidental reuse of invalid PagingSources, which gave an unclear error (I99809, b/158486430)
  • Failures from RemoteMediator REFRESH no longer prevent PagingSource from loading (I38b1b, b/158892717)
  • The non-suspending version of submitData no longer causes a crash due to concurrent collection on multiple PagingData when called after the suspending version of submitData. (I26358, b/158048877)
  • Fixed "cannot collect twice from pager" exception that could occur after config change (I58bcc, b/158784811)

Version 3.0.0-alpha01

June 10, 2020

androidx.paging:paging-*:3.0.0-alpha01 is released. Version 3.0.0-alpha01 contains these commits.

The Paging Library has updated to 3.0, to enable several major new features.

New Features of 3.0

Known Issues

  • Paging 3 javadocs are not yet available. In the interim, please use the guides linked above or the Kotlin docs. (b/158614050)

Version 2.1.2

Version 2.1.2

March 18, 2020

androidx.paging:paging:2.1.2 is released. Version 2.1.2 contains these commits against 2.1.0.

Bug Fixes

  • Fix for IndexOutOfBoundsException in rare cases when converting a position during invalidation.

Release issue

  • Paging version 2.1.1 was released incorrectly from a misconfigured branch, exposing partially-implemented APIs and functionality upcoming in a future release.

  • Paging 2.1.2 contains the load-centering fix originally released in 2.1.1, but this time correctly cherry-picked atop the 2.1.0 release. It is strongly recommended to upgrade to this release, if you are currently on 2.1.1.

Version 2.1.1

Version 2.1.1

December 18, 2019

androidx.paging:paging-*:2.1.1 is released. Version 2.1.1 contains these commits.

Bug fixes

  • Contiguous initial loads from PositionalDataSources are now centered around last access when placeholders disabled

Version 2.1.0

Version 2.1.0

January 25, 2019

Paging 2.1.0 is released with no changes from 2.1.0-rc01.

Version 2.1.0-rc01

December 6, 2018

Paging 2.1.0-rc01 is released with no changes from 2.1.0-beta01.

Version 2.1.0-beta01

November 1, 2018

Paging 2.1.0-beta01 is released with no changes from 2.1.0-alpha01.

Version 2.1.0-alpha01

October 12, 2018

Paging 2.1.0-alpha01 has two major additions - page dropping, and KTX extension libraries for every artifact - as well as several other API changes and bugfixes.

API Changes

  • Added PagedList.Config.Builder.setMaxSize() for limiting the number of loaded items in memory.
  • Added androidx.paging.Config() as a Kotlin alternative for PagedList.Config.Builder
  • Added androidx.paging.PagedList() as a Kotlin alternative for PagedList.Builder
  • Added DataSourceFactory.toLiveData() as a Kotlin alternative for LivePagedListBuilder
  • Added DataSourceFactory.toObservable() and toFlowable() as Kotlin alternatives for RxPagedListBuilder
  • Added AsyncPagedListDiffer.addPagedListListener() for listening to when PagedList is swapped. b/111698609
  • Added PagedListAdapter.onCurrentListChanged() variant that passes old and new list, deprecated previous variant.
  • Added PagedListAdapter/AsyncPagedListDiffer.submitList() variants which take an additional callback that triggers if/when the pagedlist is displayed, after diffing. This allows you to synchronize a PagedList swap with other UI updates. b/73781068
  • PagedList.getLoadedCount() added to let you know how many items are in memory. Note that the return value is always equal to .size() if placeholders are disabled.

Bug Fixes

  • Fixed a race condition when diffing if lists are reused b/111591017
  • PagedList.loadAround() now throws IndexOutOfBoundsException when index is invalid. Previously it could crash with an unclear other exception.
  • Fixed a case where an extremely small initial load size together with unchanged data would result in no further loading b/113122599

Version 2.0.0

Version 2.0.0

October 1, 2018

Paging 2.0.0 is released with a single bugfix.

Bug Fixes

  • Fixed a crash that could occur with very fast scrolling using PositionalDataSource and placeholders b/114635383.

Version 2.0.0-beta01

July 2, 2018

Bug Fixes

  • Fixed content disappearing in some prepend cases (placeholders disabled, PositionalDataSource) b/80149146
  • (Already released in 1.0.1) Fixed crashes where PagedListAdapter and AsyncPagedListDiffer would fail to signal move events. b/110711937

Pre-AndroidX Dependencies

For the pre-AndroidX versions of Paging that follow, include these dependencies:

dependencies {
    def paging_version = "1.0.0"

    implementation "android.arch.paging:runtime:$paging_version"

    // alternatively - without Android dependencies for testing
    testImplementation "android.arch.paging:common:$paging_version"

    // optional - RxJava support
    implementation "android.arch.paging:rxjava2:$paging_version"
}

Version 1.0.1

Version 1.0.1

June 26, 2018

Paging 1.0.1 is released with a single bugfix in runtime. We highly recommend using 1.0.1 for stability. Paging RxJava2 1.0.1 is also released, and is identical to 1.0.0-rc1.

Bug Fixes

  • Fixed crashes where PagedListAdapter and AsyncPagedListDiffer would fail to signal move events. b/110711937

RxJava2 Version 1.0.0

RxJava2 Version 1.0.0-rc1

May 16, 2018

Paging RxJava2 1.0.0-rc1 is moving to release candidate with no changes from the initial alpha.

Version 1.0.0

Version 1.0.0-rc1

April 19, 2018 Paging Release Candidate

We do not have any more known issues or new features scheduled for the Paging 1.0.0 release. Please upgrade your projects to use 1.0.0-rc1 and help us battle test it so that we can ship a rock solid 1.0.0.

There are no changes in this release, it is the same as 1.0.0-beta1.

Version 1.0.0-beta1

April 5, 2018

Paging will be in beta for a short time before progressing to release candidate. We are not planning further API changes for Paging 1.0, and the bar for any API changes is very high.

Alpha RxJava2 support for Paging is released as a separate optional module (android.arch.paging:rxjava2:1.0.0-alpha1) and will temporarily be versioned separately until it stabilizes.

This new library provides an RxJava2 alternative to LivePagedListBuilder, capable of constructing Observables and Flowables, taking Schedulers instead of Executors:

Kotlin

val pagedItems = RxPagedListBuilder(myDataSource, /* page size */ 50)
        .setFetchScheduler(myNetworkScheduler)
        .buildObservable()

Java

Observable<PagedList<Item>> pagedItems =
        RxPagedListBuilder(myDataSource, /* page size */ 50)
                .setFetchScheduler(myNetworkScheduler)
                .buildObservable();

New Features

  • RxPagedListBuilder is added via the new android.arch.paging:rxjava2 artifact.

API Changes

  • API changes to clarify the role of executors in builders:

    • Renamed setBackgroundThreadExecutor() to setFetchExecutor() (in PagedList.Builder and LivePagedListBuilder)

    • Renamed setMainThreadExecutor() to setNotifyExecutor() (in PagedList.Builder).

  • Fixed PagedList.mCallbacks member to be private.

Bug Fixes

  • LivePagedListBuilder triggers initial PagedList load on the specified executor, instead of the Arch Components IO thread pool.

  • Fixed invalidate behavior in internal DataSource wrappers (used to implement DataSource.map, as well as placeholder-disabled PositionalDataSource loading) b/77237534

Version 1.0.0-alpha7

March 21, 2018

Paging 1.0.0-alpha7 is released alongside Lifecycles 1.1.1. As Paging alpha7 depends on the move of the Function class mentioned above, you will need to update your lifecycle:runtime dependency to android.arch.lifecycle:runtime:1.1.1.

Paging alpha7 is planned to be the final release before Paging hits beta.

API Changes

  • DataSource.LoadParams objects now have a public constructor and DataSource.LoadCallback objects are now abstract. This enables wrapping a DataSource or directly testing a DataSource with a mock callback. b/72600421
  • Mappers for DataSource and DataSource.Factory
    • map(Function<IN,OUT>) allows you to transform, wrap, or decorate results loaded by a DataSource.
    • mapByPage(<List<IN>,List<OUT>>) enables the same for batch processing (e.g. if items loaded from SQL need to additionally query a separate database, that can be done as a batch.)
  • PagedList#getDataSource() is added as a convenience method b/72611341
  • All deprecated classes have been removed from the API, including the remains of recyclerview.extensions package, and the LivePagedListProvider.
  • DataSource.Factory is changed from an interface to an abstract class to enable map functionality.

Bug Fixes

  • Changed Builders to be final. b/70848565
  • Room DataSource implementation is now fixed to handle multi-table queries - this fix is contained within Room 1.1.0-beta1, see above.
  • Fixed a bug where BoundaryCallback.onItemAtEndLoaded would not be invoked for PositionalDataSource if placeholders are enabled and the total size is an exact multiple of the page size.

Version 1.0.0-alpha5

January 22, 2018

Bug Fixes

  • Fix page loading when placeholders are disabled b/70573345
  • Additional logging for tracking down IllegalArgumentException bug b/70360195 (and speculative Room-side fix)
  • Javadoc sample code fixes b/70411933, b/71467637