FragmentStatePagerAdapter crashes when replacing fragments using new behavior [137209870]

Fixed

Bug

Status Update

No update yet.

Description

pe...@airbnb.com

created issue #1

Jul 11, 2019 03:26AM

Component used: Fragment
Version used: 1.1.0-rc01 (part of AppCompat 1.1.0-rc01)
Devices/Android versions reproduced on: API 28 x86 emulator and Pixel 1

When using the new `BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT` behavior on a `FragmentStatePagerAdapter`, along with `getItemPosition()` returning `POSITION_NONE`, the app crashes when calling `notifyDataSetChanged()` on the adapter. We are using this paradigm to replace all of the fragments in the adapter.

Here's what seems to be happening. All of the fragments are removed in a fragment transaction (`ViewPager` calls `FragmentStatePagerAdapter#finishUpdate()` once the fragments are removed). Then the new fragments are instantiated and added to a new fragment transaction. The `ViewPager` then calls `setPrimaryItem` which tries to set the max lifecycle on the `mCurrentPrimaryItem`. However, this `mCurrentPrimaryItem` is still referencing the old fragment that was removed in a separate transaction, which causes the crash. It seems like the `mCurrentPrimaryItem` should be nulled out if it is removed from the adapter.

I've attached a sample project and GIF. To reproduce, just launch the app and press the `Replace Fragments` action button. Here's the error stacktrace:

2019-07-10 20:03:16.876 32176-32176/com.example.android.horizontalpaging E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.android.horizontalpaging, PID: 32176
java.lang.IllegalArgumentException: Cannot setMaxLifecycle for Fragment not attached to FragmentManager FragmentManager{9187988 in HostCallbacks{ba35f21}}
at androidx.fragment.app.BackStackRecord.setMaxLifecycle(BackStackRecord.java:244)
at androidx.fragment.app.FragmentStatePagerAdapter.setPrimaryItem(FragmentStatePagerAdapter.java:234)
at androidx.viewpager.widget.ViewPager.populate(ViewPager.java:1234)
at androidx.viewpager.widget.ViewPager.setCurrentItemInternal(ViewPager.java:669)
at androidx.viewpager.widget.ViewPager.setCurrentItemInternal(ViewPager.java:631)
at androidx.viewpager.widget.ViewPager.dataSetChanged(ViewPager.java:1086)
at androidx.viewpager.widget.ViewPager$PagerObserver.onChanged(ViewPager.java:3097)
at androidx.viewpager.widget.PagerAdapter.notifyDataSetChanged(PagerAdapter.java:291)
at com.example.android.horizontalpaging.MainActivity.onOptionsItemSelected(MainActivity.java:67)
at android.app.Activity.onMenuItemSelected(Activity.java:3544)
at androidx.fragment.app.FragmentActivity.onMenuItemSelected(FragmentActivity.java:384)
at com.android.internal.policy.PhoneWindow.onMenuItemSelected(PhoneWindow.java:1237)
at com.android.internal.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:776)
at com.android.internal.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:148)
at com.android.internal.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:923)
at com.android.internal.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:913)
at android.widget.ActionMenuView.invokeItem(ActionMenuView.java:617)
at com.android.internal.view.menu.ActionMenuItemView.onClick(ActionMenuItemView.java:147)
at android.view.View.performClick(View.java:6597)
at android.view.View.performClickInternal(View.java:6574)
at android.view.View.access$3100(View.java:778)
at android.view.View$PerformClick.run(View.java:25885)
at android.os.Handler.handleCallback(Handler.java:873)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6718)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

FragmentStatePagerCrash.gif

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HorizontalPaging.zip

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Comments

pe...@airbnb.com <pe...@airbnb.com> #2Jul 11, 2019 03:27AM

Yigit, do you have time to fix it?

reemission of the same liveData is racy

il...@google.com <il...@google.com> Jul 11, 2019 02:16PM

Assigned to jb...@google.com.

ap...@google.com <ap...@google.com> #3Jul 11, 2019 10:54PM

yea i'll take it.

jb...@google.com <jb...@google.com> #4Jul 11, 2019 10:55PM

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.

an...@google.com <an...@google.com> #5Jul 12, 2019 09:20PM

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()
}
}

da...@gmail.com <da...@gmail.com> #6Jul 17, 2019 04:53AM

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)

il...@google.com <il...@google.com> #7Jul 17, 2019 05:22PM

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} )
}

ya...@gmail.com <ya...@gmail.com> #8Jul 21, 2019 05:17PM

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

il...@google.com <il...@google.com> #9Jul 22, 2019 05:00AM

Re #8 - you'll need to *compile* against API 29 (that'll be true for 1.1.0-rc01 and all future versions of AppCompat), but there's no requirement to *target* API 29 - those are entirely different things as per

https://medium.com/androiddevelopers/picking-your-compilesdkversion-minsdkversion-targetsdkversion-a098a0341ebd