OnDestinationChangedListener won't get called if it navigates somewhere in response to current destination. [190228815]

Fixed

Bug

Status Update

No update yet.

Description

sh...@google.com

created issue #1

Jun 4, 2021 10:40PM

Component used: Navigation Version used: 2.3.5 Devices/Android versions reproduced on: Irrelevant ;)

Repro steps:

In a OnDestinationChangedListener, set things up so that if the new destination is A, nav to B.
Set the current destination to A.
Add the OnDestinationChangedListener to the NavController.

Expected Result: OnDestinationChangedListener receives callback when it is set, and then receives a callback when it causes navigation to B.

Actual Result: OnDestinationChangedListener receives callback when it is set, and then DOES NOT receive a callback when it causes navigation to B.

After the OnDestinationChangedListener is set, this sort of reentrant call works as would be expected, but when getting the callback after having set the OnDestinationChangedListener, it does not.

I think this simply requires swapping

mOnDestinationChangedListeners.add(listener);

and

if (!mBackStack.isEmpty()) {
            NavBackStackEntry backStackEntry = mBackStack.peekLast();
            listener.onDestinationChanged(this, backStackEntry.getDestination(),
                    backStackEntry.getArguments());
        }

in NavController.java. :)

Comments

il...@google.com <il...@google.com> #2Jun 4, 2021 10:57PM

Yigit, do you have time to fix it?

reemission of the same liveData is racy

il...@google.com <il...@google.com> Jun 8, 2021 07:26PM

Assigned to il...@google.com.

il...@google.com <il...@google.com> Jun 9, 2021 12:00AM

Accepted by il...@google.com.

ap...@google.com <ap...@google.com> #3Jun 9, 2021 03:05AM

yea i'll take it.

il...@google.com <il...@google.com> #4Jun 9, 2021 03:42AM

Marked as fixed.

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.

sh...@google.com <sh...@google.com> #5Jun 11, 2021 05:07PM

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()
}
}

Issue 190228815