IssueTracker

Yigit, do you have time to fix it?

reemission of the same liveData is racy

yea i'll take it.

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.

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()
        }
    }

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)

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} )
        }

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

Dialog fragments are now used in all modern applications and this is the last missing piece of puzzle to really switch everything to Navigation component.
Hope to see support for this soon enough.

Please, any update on this?

Sometime, there's need to display the previous fragment along with new fragment which is more of like a dialog. Therefore, it will be nice to have this feature in the next update.

This would be really useful, especially since Modal Bottom Sheets need to be implemented as BottomSheetDialogFragments.  It would be great to get all of our navigation into the navigation graph.

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

commit eec025be7822df951131cc0766b928383f58789e
Author: Ian Lake <ilake@google.com>
Date:   Mon Apr 22 14:51:05 2019

    Add support for <dialog> destinations
   
    Add support for using a DialogFragment as
    a destination in your navigation graph via
    the <dialog> tag.
   
    Test: added tests, tested in testapp
    BUG: 80267254
    Change-Id: I82daaa7bde4efe782095eee7b3932092e9086adb

M       navigation/fragment/api/2.1.0-alpha03.txt
M       navigation/fragment/api/current.txt
M       navigation/fragment/ktx/api/2.1.0-alpha03.txt
M       navigation/fragment/ktx/api/current.txt
A       navigation/fragment/ktx/src/androidTest/java/androidx/navigation/fragment/DialogFragmentNavigatorDestinationBuilderTest.kt
A       navigation/fragment/ktx/src/main/java/androidx/navigation/fragment/DialogFragmentNavigatorDestinationBuilder.kt
A       navigation/fragment/src/main/java/androidx/navigation/fragment/DialogFragmentNavigator.java
M       navigation/fragment/src/main/java/androidx/navigation/fragment/NavHostFragment.java
M       navigation/fragment/src/main/res/values/attrs.xml
A       navigation/integration-tests/testapp/src/main/java/androidx/navigation/testapp/LearnMoreDialogFragment.kt
M       navigation/integration-tests/testapp/src/main/java/androidx/navigation/testapp/MainFragment.kt
M       navigation/integration-tests/testapp/src/main/res/layout/main_fragment.xml
M       navigation/integration-tests/testapp/src/main/res/navigation/nav_main.xml
M       navigation/integration-tests/testapp/src/main/res/values/strings.xml

https://android-review.googlesource.com/949238
https://goto.google.com/android-sha1/eec025be7822df951131cc0766b928383f58789e

We've added support for dialog destinations internally, it'll be available in Navigation 2.1.0-alpha03

Awesome! Cheers guys

Are there any public test/demo applications one could use for reference?
Because the integration tests seem to be non public

https://stackoverflow.com/q/56647476/7972699

i have tried using dialog as destination it work's fine but when i navigate from dialog to fragment/dialog i am getting runtime error as NavController is missing.

i am using 2.1.0-alpha05

Very useful, fixed also.Cheers!