IssueTracker

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)