[ViewPager2] Support NavHostFragment inside ViewPager2 [133640271]

Fixed

Bug

Status Update

No update yet.

Description

an...@gmail.com

created issue #1

May 27, 2019 12:43PM

Use case:
Would like to use an existing app layout and take benefit of offscreen screen "caching"

The issue
Currently if I attempt to use NavHostFragment in combination with ViewPager2 and FragmentStateAdapter I'll get the following runtime exception due to uninitialised containterViewId (stack trace below).

If I change FragmentStateAdapter.placeFragmentInViewHolder
From:

// { f:notAdded, v:notCreated, v:notAttached } -> add, create, attach
if (!shouldDelayFragmentTransactions()) {
scheduleViewAttach(fragment, container);
mFragmentManager.beginTransaction().add(fragment, "f" + holder.getItemId()).commitNow();
}

To:

// { f:notAdded, v:notCreated, v:notAttached } -> add, create, attach
if (!shouldDelayFragmentTransactions()) {
mFragmentManager.beginTransaction().add(container.getId(), fragment, "f" + holder.getItemId()).commitNow();
}

The issue is solved. Testing a couple of scenarios did not reveal any side effects, but as I have yet to familiarise myself with the details of the implementation I'm not sure if it will not have any negative side effects.

Happy to put up a PR for this, but would like to understand better why the fragment is being added this way in the current state of the adapter.

Stack trace:

java.lang.IllegalArgumentException: Must use non-zero containerViewId
at androidx.fragment.app.FragmentTransaction.replace(FragmentTransaction.java:223)
at androidx.fragment.app.FragmentTransaction.replace(FragmentTransaction.java:200)
at androidx.navigation.fragment.FragmentNavigator.navigate(FragmentNavigator.java:181)
at androidx.navigation.fragment.FragmentNavigator.navigate(FragmentNavigator.java:58)
at androidx.navigation.NavGraphNavigator.navigate(NavGraphNavigator.java:80)
at androidx.navigation.NavGraphNavigator.navigate(NavGraphNavigator.java:30)
at androidx.navigation.NavController.navigate(NavController.java:877)
at androidx.navigation.NavController.onGraphCreated(NavController.java:524)
at androidx.navigation.NavController.setGraph(NavController.java:482)
at androidx.navigation.NavController.setGraph(NavController.java:447)
at androidx.navigation.fragment.NavHostFragment.onCreate(NavHostFragment.java:248)
at androidx.fragment.app.Fragment.performCreate(Fragment.java:2613)
at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:831)
at androidx.fragment.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManagerImpl.java:1228)
at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:1293)
at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:439)
at androidx.fragment.app.FragmentManagerImpl.executeOps(FragmentManagerImpl.java:2066)
at androidx.fragment.app.FragmentManagerImpl.executeOpsTogether(FragmentManagerImpl.java:1856)
at androidx.fragment.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManagerImpl.java:1811)
at androidx.fragment.app.FragmentManagerImpl.execSingleAction(FragmentManagerImpl.java:1686)
at androidx.fragment.app.BackStackRecord.commitNow(BackStackRecord.java:293)
at androidx.viewpager2.adapter.FragmentStateAdapter.placeFragmentInViewHolder(FragmentStateAdapter.java:284)
at androidx.viewpager2.adapter.FragmentStateAdapter.onViewAttachedToWindow(FragmentStateAdapter.java:222)
at androidx.viewpager2.adapter.FragmentStateAdapter.onViewAttachedToWindow(FragmentStateAdapter.java:61)
at androidx.recyclerview.widget.RecyclerView.dispatchChildAttached(RecyclerView.java:7433)
at androidx.recyclerview.widget.RecyclerView$5.addView(RecyclerView.java:862)
at androidx.recyclerview.widget.ChildHelper.addView(ChildHelper.java:107)
at androidx.recyclerview.widget.RecyclerView$LayoutManager.addViewInt(RecyclerView.java:8478)
at androidx.recyclerview.widget.RecyclerView$LayoutManager.addView(RecyclerView.java:8436)
at androidx.recyclerview.widget.RecyclerView$LayoutManager.addView(RecyclerView.java:8424)
at androidx.recyclerview.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1641)
at androidx.recyclerview.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1587)
at androidx.recyclerview.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:665)
at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:4040)
at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:3757)
at androidx.recyclerview.widget.RecyclerView.onLayout(RecyclerView.java:4310)

Comments

jg...@google.com <jg...@google.com> #2May 31, 2019 11:45AM

Nested scrolling works partially (as per

http://b/122818889). Let's discuss if we need full support and if so make sure it works.

jg...@google.com <jg...@google.com> #3May 31, 2019 11:46AM

Hi!

What is 'partially' exactly?
How do I see it?
Thanks!

an...@gmail.com <an...@gmail.com> #4Jun 2, 2019 10:03AM

As of now:
- Nesting scroll views with a scroll direction perpendicular to the ViewPager2's orientation inside ViewPager2 works
- Nesting scroll views with a scroll direction parallel to the ViewPager2's orientation inside ViewPager2 does not work

sample.zip

1.6 MB

Download

an...@gmail.com <an...@gmail.com> #5Jun 2, 2019 11:43AM

Horizontal ViewPager2 not correctly working into a vertical RecyclerView
Set a setNestedScrollingEnabled to the RecyclerView into the ViewPager2 (across reflection) resolves the problem

sample2.zip

2.7 MB

Download

jg...@google.com <jg...@google.com> Jul 2, 2019 03:38PM

Assigned to jg...@google.com.

jg...@google.com <jg...@google.com> #6Aug 14, 2019 05:31PM

ageevvalentin@gmail.com, could you provide a sample app? I'd like to learn more about the circumstances that cause the problem; putting a clean ViewPager2 inside a clean RecyclerView seems to work fine, so there must be other factors involved.

il...@google.com <il...@google.com> #7Aug 20, 2019 04:38PM

Added a patch for androidx-master-dev that demos a horizontal ViewPager2 inside a vertical RecyclerView.

Verified that it works correctly on a:
- Nexus 4 emulator with API 17
- Nexus 5X emulator with API 28
- Pixel 2 device with API 29

To reproduce:
- Check out the Android Jetpack source (at commit 256899f482ff85cddfb050f37550be7b5ec927ef) (see steps in [1])
- Apply the patch (`git apply 0001-Add-sample-where-a-horizontal-ViewPager2-is-nested-i.patch`)
- Build and install viewpager2's integration-tests app: `./gradlew viewpager2:integration-tests:testapp:installDebug`
- Run it

Closing the issue for now, but please reopen if you have a minimal reproduction app

[1]

https://android.googlesource.com/platform/frameworks/support/+/256899f482ff85cddfb050f37550be7b5ec927ef

jg...@google.com <jg...@google.com> #8Sep 24, 2019 04:16PM

Marked as fixed.

Re-opening as requested by a few users. Narrowed down the focus to nested scrolling elements with the same scroll direction.