Provider interop between SavedStateHandle and Compose Saver/SaveableStateRegistry [195689777]

Fixed

Feature Request

Status Update

No update yet.

Description

va...@google.com

created issue #1

Aug 5, 2021 10:14PM

Compose provides rememberSaveable, along with accompanying tools like Saver and SaveableStateRegistry as its mechanisms for storing saved instance state. Currently, there isn't a provided interoperability layer between these tools and SavedStateHandle.

If SavedStateHandle isn't used in the ViewModel, state that is hoisted from @Composables to ViewModels won't be stored to saved instance state. This might either cause bugs due to state loss upon process death, or act as a barrier to hoisting state sufficiently if it seems like rememberSaveable has to be used to remember state across process recreation.

The proposal is to provide the necessary hooks for SavedStateHandle with Saver so that any state holder that is being saved via rememberSaveable could also be saved with SavedStateHandle.

Comments

il...@google.com <il...@google.com> Nov 18, 2021 10:12PM

Status: New

il...@google.com <il...@google.com> #2Jan 5, 2022 09:42PM

Yigit, do you have time to fix it?

reemission of the same liveData is racy

va...@google.com <va...@google.com> #3Jan 5, 2022 10:22PM

yea i'll take it.

il...@google.com <il...@google.com> Feb 17, 2022 07:20PM

Assigned to jb...@google.com.

al...@gmail.com <al...@gmail.com> #4Mar 11, 2022 10:38AM

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.

va...@google.com <va...@google.com> #5Mar 14, 2022 05:59PM

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()
}
}

ap...@google.com <ap...@google.com> #6Mar 16, 2022 06:22PM

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)

jb...@google.com <jb...@google.com> #7Mar 17, 2022 03:58AM

Marked as fixed.

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} )
}