Paging should be able to do append/prepend in an early list after a refresh failure [189967519]

Feature Request

Status Update

No update yet.

Description

pe...@gmail.com

created issue #1

Jun 2, 2021 08:06PM

Component used: androidx.paging:paging-runtime-ktx
Version used: 3.0.0
Devices/Android versions reproduced on: Samsung J3 (Android 8), Emulator (Android 11)

Hello,

If the paging adapter has some data and is refreshed via adapter.refresh with (for example) swipe to refresh, then if the refresh fails, the paging stops working. Moreover, if there was an ongoing append that doesn't finish before the refresh error and the LoadStateFooter was displayed, it never disappears.

I believe this to be a common use case and the paging should continue even after refresh error.

Thank you.

- Attached screen recording of both issues
- Reproducible in the paging sample

https://github.com/android/architecture-components-samples/tree/main/PagingWithNetworkSample

Comments

pe...@gmail.com <pe...@gmail.com> #2Jun 2, 2021 08:07PM

Hello, can you please attach a sample that reproduces your error?

bug1.mp4

1.5 MB

Download

bug2.mp4

2 MB

Download

pe...@gmail.com <pe...@gmail.com> #3Jul 26, 2021 08:23PM

I’ve attached two screen recordings demonstrating the mediator's behavior during the first and second launches after installation. Additionally, https://gist.github.com/yatiksihag01/20106aa4855bd438e3eb982034d4bb7d is link to a GitHub Gist containing the code for my remote mediator file for your reference.

yb...@google.com <yb...@google.com> #4Oct 16, 2021 01:41AM

Based on first_launch_after_installation.mp4, your paging state is indeed showing null for nextKey, so it makes sense that Paging concluded there are no more items to load.

So I think the question is why the PagingState contains only an empty page and null values. My guess is either

RemoteMediator REFRESH actually returned empty data - what is the returned allNewsItems value on initial REFRESH?
RemoteMediator REFRESH successfully loaded data and inserted it into database, but Paging hasn't processed that yet by the time Append is triggered, so PagingState is empty.

The second case doesn't seem likely though.

If you attach an executable app, I can look into this further.

Otherwise, you may gain more insight through Paging logs with adb shell setprop log.tag.Paging VERBOSE. You can also try implementing RemoteKeys in this codelab which addresses possible races between Refresh and subsequent loads.

du...@google.com <du...@google.com> #5Oct 16, 2021 05:18AM

Hey! I ran into this same issue. It is in fact the second case you mentioned and is documented here.

I've published a repo reproducing the issue and filed a ticket proposing how this could be changed.

pe...@gmail.com <pe...@gmail.com> #6Oct 16, 2021 08:03AM

Sorry about the vague description but that's exactly the issue. If the remote refresh triggered via adapter.refresh fails, the previous generation stops working.

And there seems to be no way out of it. Plus, If there was a loading footer, it never disappears. It's stuck.

yb...@google.com <yb...@google.com> #7Oct 16, 2021 04:00PM

This is a reasonable feature request but due to how paging works internally, it won't be easy to support (except for the footer bug, that looks like a bug :) )

du...@google.com <du...@google.com> Aug 4, 2022 04:20PM

Reassigned to cl...@google.com.

cl...@google.com <cl...@google.com> Aug 23, 2022 06:46PM

Status: New