[Paging3] loading of data not fully triggered when using small pages. [169259468]

Fixed

Bug

Status Update

No update yet.

Description

jd...@xooloo.com

created issue #1

Sep 24, 2020 08:59AM

Component used: Paging3 Version used: alpha06 Devices/Android versions reproduced on: Android 7.1

I'm presenting a list of items using data from a room DB.

    fun getMessages(chat: Chat): Pager<Int, Message> {
        return Pager(
                PagingConfig(pageSize = 3, enablePlaceholders = true)
        ) {
            db.messages.getMessages(chat.id)
        }
    }

Note: The page size is intentionally low to try to debug paging issues, but is higher in production code.

The pager flow is used to produce PagingData passed to a PagingAdapter.

chats.getMessages(chat).flow.map {
  it.map { message -> getEntryForMessages(chatWithUsers, message) }
}.collect {
  adapter.submitList(it)
}

The RecyclerView uses a simple LinearLayoutManager.

Everything work mostly fine except that that latest entry may never be loaded while scrolling (especially when scrolling slowly). The PagingData properly provides a placeholder that is shown in the list, but it never trigger the loading of the last data, and so never replace the placeholder when reaching the end of the list.

Comments

du...@google.com <du...@google.com> #2Sep 24, 2020 01:16PM

Just to let you know that this issue present in the latest available release. I did just update to alpha09 and it breaks my code. My PagingSource if a Room backed source, but I have the same issue: the paging library failed to generate a separator for the first item.

It is still working with the alpha08.

jd...@xooloo.com <jd...@xooloo.com> #3Sep 28, 2020 10:17AM

Project: platform/frameworks/support
Branch: androidx-master-dev

commit aa90cc2cb835209e12964d3afbc91e96b6d4e36b
Author: Dustin Lam <dustinlam@google.com>
Date: Tue Nov 24 11:34:08 2020

Add empty terminal insert for separators support with RemoteMediator

Re-applies a previous hack which inserted empty insert events to allow
separators to add terminal separators (header / footer), since
Separators may need to wait for a LoadStateUpdate event to mark terminal
load state from RemoteMediator.

Fixes: 172254056
Test: ./gradlew paging:paging-common:test
Change-Id: I5c5f2ac3860889909a30cd322a1e7b36eec1a9fd

M paging/common/src/main/kotlin/androidx/paging/MutableLoadStateCollection.kt
M paging/common/src/main/kotlin/androidx/paging/PageEvent.kt
M paging/common/src/main/kotlin/androidx/paging/PageFetcher.kt
M paging/common/src/main/kotlin/androidx/paging/Separators.kt
M paging/common/src/test/kotlin/androidx/paging/PageFetcherSnapshotTest.kt
M paging/common/src/test/kotlin/androidx/paging/SeparatorsTest.kt
M paging/integration-tests/testapp/src/main/java/androidx/paging/integration/testapp/room/CustomerDao.java
M paging/integration-tests/testapp/src/main/java/androidx/paging/integration/testapp/v3room/NetworkCustomerPagingSource.kt
M paging/integration-tests/testapp/src/main/java/androidx/paging/integration/testapp/v3room/V3RemoteMediator.kt
M paging/integration-tests/testapp/src/main/java/androidx/paging/integration/testapp/v3room/V3RoomAdapter.kt
M paging/integration-tests/testapp/src/main/java/androidx/paging/integration/testapp/v3room/V3RoomViewModel.kt

https://android-review.googlesource.com/1510174

Screenshot_20200928-120938.png

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du...@google.com <du...@google.com> #4Sep 28, 2020 10:04PM

Accepted by du...@google.com.

Thanks for providing a sample project! Looks like this is an issue with how we conflate item accesses when triggering prefetch.

ap...@google.com <ap...@google.com> #5Oct 1, 2020 07:51PM

Marked as fixed.

Project: platform/frameworks/support
Branch: androidx-master-dev

commit 190a76ec743552627310e024976fd5896e989acb
Author: Dustin Lam <dustinlam@google.com>
Date: Mon Sep 28 13:54:08 2020

Prioritize hints from more recent presenter state

Currently we only use itemsPresentedAfter, which only accounts for the
placeholderOffset from the last page, but this value is insufficient to
determine which hint loads more items in cases where the last/first
pageOffset changes on presenter side.

As a result, we'll drop hints that would load more items in favor of
hints that came from a past presenter state that was scroll further into
placeholders.

This change fixes the above by always prioritizing new incoming hints if
the first/last pageOffset of presenter state changes.

RelNote: "N/A"
Fixes: 169259468
Test: ./gradlew paging:paging-common:test
Change-Id: Iffda3a0eb7abe162045893367b4781daf75adb01

M paging/common/api/current.txt
M paging/common/api/public_plus_experimental_current.txt
M paging/common/api/restricted_current.txt
M paging/common/src/main/kotlin/androidx/paging/PageFetcherSnapshot.kt
M paging/common/src/test/kotlin/androidx/paging/PageFetcherSnapshotTest.kt

https://android-review.googlesource.com/1441095

Issue 169259468

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Issue summary

Comments

du...@google.com <du...@google.com> #2Sep 24, 2020 01:16PM

jd...@xooloo.com <jd...@xooloo.com> #3Sep 28, 2020 10:17AM

du...@google.com <du...@google.com> #4Sep 28, 2020 10:04PM

ap...@google.com <ap...@google.com> #5Oct 1, 2020 07:51PM

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