navigateUp() causes navgraph issue when moving from FragmentTypeB to FragmentTypeB [123552990]

Fixed

Bug

Status Update

No update yet.

Description

an...@seventhbeam.com

created issue #1

Jan 29, 2019 06:09AM

Component used: Navigation
Version used: 1.0.0-alpha11

I'm seeing some strange behaviour when pressing back button and transistion back to a fragment from a fragment of the same id.
My app uses some generic fragment structures that are driven by args passed in, as such there are places like:

FragmentA -> FragmentB -> FragmentB -> FragmentC

However if the back button is pressed on the second instance of FragmentB, FragmentA is replaced in the navhost while the navgraph correctly displays in the toolbar. Forward navigation from this point however is missing from the navgraph and results in an IllegalStateException with the action 'not found' in the graph, unless the back button is pressed again (pushing the navgraph destination back to FragmentA)

Is this intended behaviour? If so is there a way to declare FragmentB as 'stackable'?

Comments

so...@gmail.com <so...@gmail.com> #2Jan 29, 2019 10:56AM

Yigit, do you have time to fix it?

reemission of the same liveData is racy

so...@gmail.com <so...@gmail.com> #3Jan 29, 2019 11:07AM

yea i'll take it.

so...@gmail.com <so...@gmail.com> #4Jan 29, 2019 11:34AM

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.

il...@google.com <il...@google.com> Jan 29, 2019 04:05PM

Assigned to il...@google.com.

il...@google.com <il...@google.com> Jan 30, 2019 06:49PM

Accepted by il...@google.com.

ap...@google.com <ap...@google.com> #5Jan 30, 2019 07:50PM

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()
}
}

il...@google.com <il...@google.com> #6Jan 30, 2019 08:33PM

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)

ch...@gmail.com <ch...@gmail.com> #7Feb 5, 2019 06:44PM

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} )
}

il...@google.com <il...@google.com> #8Feb 5, 2019 06:50PM

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

commit af12e75e6b4110f48e44ca121466943909de8f06
Author: Yigit Boyar <yboyar@google.com>
Date: Tue Sep 03 12:58:11 2019

Fix coroutine livedata race condition

This CL fixes a bug in liveData builder where emitting same
LiveData source twice would make it crash because the second
emission registry could possibly happen before first one is
removed as source.

We fix it by using a suspending dispose function. It does feel
a bit hacky but we cannot make DisposableHandle.dispose async
and we do not want to block there. This does not mean that there
is a problem if developer disposes it manually since our emit
functions take care of making sure it disposes (and there is
no other way to add source to the underlying MediatorLiveData)

Bug: 140249349
Test: BuildLiveDataTest#raceTest_*

Change-Id: I0b464c242a583da4669af195cf2504e2adc4de40

M lifecycle/lifecycle-livedata-ktx/api/2.2.0-alpha05.txt
M lifecycle/lifecycle-livedata-ktx/api/current.txt
M lifecycle/lifecycle-livedata-ktx/api/public_plus_experimental_2.2.0-alpha05.txt
M lifecycle/lifecycle-livedata-ktx/api/public_plus_experimental_current.txt
M lifecycle/lifecycle-livedata-ktx/api/restricted_2.2.0-alpha05.txt
M lifecycle/lifecycle-livedata-ktx/api/restricted_current.txt
M lifecycle/lifecycle-livedata-ktx/src/main/java/androidx/lifecycle/CoroutineLiveData.kt
M lifecycle/lifecycle-livedata-ktx/src/test/java/androidx/lifecycle/BuildLiveDataTest.kt

https://android-review.googlesource.com/1112186

https://goto.google.com/android-sha1/af12e75e6b4110f48e44ca121466943909de8f06