Application get crashed when reached at end of List. [158892717]

Fixed

Bug

Status Update

No update yet.

Description

th...@gmail.com

created issue #1

Jun 14, 2020 08:05AM

Component used: Paging
Version used: 3.0.0-alpha01

I have followed codelabs paging 3 tutorial. I have implemented paging from network and database.
This is the repository provided by codelabs tutorial :-

https://github.com/googlecodelabs/android-paging

I have founded 2 issues in Paging 3.

1. Application get crashed when Recylerview reach at end(last page).
Inside GithubRemoteMediator.kt
I have set val endOfPaginationReached = page > 2 to allow maximum 2 pages for testing.
So, the problem is when I reach at the last page of list, application get crashed as remoteKeys.nextKey is null(as we have set nextKey=null for last page of list).

2. Offline cache broken
How to support caching when application is open without internet connection. currently it is showing retry button. How to show previously loaded data. I have tried to fix this by removing

// clear all tables in the database
if (loadType == LoadType.REFRESH) {
repoDatabase.remoteKeysDao().clearRemoteKeys()
repoDatabase.reposDao().clearRepos()
}

as this will now not gone delete data from database.
But still Pager does not load data available.

So how I can fix this problem?
Is there any way of detecting end of paging?
Why Pager is not returning data available in database.

Comments

du...@google.com <du...@google.com> #2Jun 15, 2020 04:16PM

Reassigned to du...@google.com.

Yigit, do you have time to fix it?

reemission of the same liveData is racy

th...@gmail.com <th...@gmail.com> #3Jun 17, 2020 09:21AM

yea i'll take it.

ap...@google.com <ap...@google.com> #4Jun 17, 2020 08:08PM

Thanks for the detailed analysis. This may not be an issue anymore since we've started using Main.immediate there but I' not sure; I'll try to create a test case.

du...@google.com <du...@google.com> #5Jun 17, 2020 08:16PM

Marked as fixed.

just emitting same live data reproduces the issue.

@Test
fun raceTest() {
val subLiveData = MutableLiveData(1)
val subject = liveData(testScope.coroutineContext) {
emitSource(subLiveData)
emitSource(subLiveData) //crashes
}
subject.addObserver().apply {
testScope.advanceUntilIdle()
}
}

du...@google.com <du...@google.com> #6Jun 17, 2020 08:18PM

With 2.2.0-alpha04 (that use Main.immediate), the issue seems to be still there (I tested it by calling emitSource() twice, like your test case)

th...@gmail.com <th...@gmail.com> #7Jun 18, 2020 03:08AM

yea sorry immediate does not fix it.
I actually have a WIP fix for it:

https://android-review.googlesource.com/c/platform/frameworks/support/+/1112186

if your case is the one i found (emitting same LiveData multiple times, as shown in #5) you can work around it by adding a dummy transformation.

val subLiveData = MutableLiveData(1)
val subject = liveData(testScope.coroutineContext) {
emitSource(subLiveData.map {it })
emitSource(subLiveData.map {it} )
}

Issue 158892717