android - Leak Canary detects memory leaks for TabLayout with ViewPager2

Question

I followed the official documentation to setup a TabLayout with ViewPager2. I used the TabLayoutMediator this way to connect the TabLayout with the ViewPager2:

TabLayoutMediator(binding.tabLayout, binding.viewPager) { tab, position ->
        tab.setIcon(getTabIcon(position))
        tab.text = getTabTitle(position)
    }.attach()

However Leak Canary detects a memory leak that seems related to the TabLayout and the TabLayoutMediator. The log is the following:

2020-05-13 17:57:32.914 D/LeakCanary: ┬───
2020-05-13 17:57:32.914 D/LeakCanary: │ GC Root: Local variable in native code
2020-05-13 17:57:32.914 D/LeakCanary: │
2020-05-13 17:57:32.914 D/LeakCanary: ├─ android.net.ConnectivityThread instance
2020-05-13 17:57:32.914 D/LeakCanary: │    Leaking: NO (PathClassLoader↓ is not leaking)
2020-05-13 17:57:32.914 D/LeakCanary: │    Thread name: 'ConnectivityThread'
2020-05-13 17:57:32.914 D/LeakCanary: │    ↓ ConnectivityThread.contextClassLoader
2020-05-13 17:57:32.914 D/LeakCanary: ├─ dalvik.system.PathClassLoader instance
2020-05-13 17:57:32.914 D/LeakCanary: │    Leaking: NO (ViewDataBinding↓ is not leaking and A ClassLoader is never leaking)
2020-05-13 17:57:32.914 D/LeakCanary: │    ↓ PathClassLoader.runtimeInternalObjects
2020-05-13 17:57:32.914 D/LeakCanary: ├─ java.lang.Object[] array
2020-05-13 17:57:32.914 D/LeakCanary: │    Leaking: NO (ViewDataBinding↓ is not leaking)
2020-05-13 17:57:32.914 D/LeakCanary: │    ↓ Object[].[349]
2020-05-13 17:57:32.914 D/LeakCanary: ├─ androidx.databinding.ViewDataBinding class
2020-05-13 17:57:32.914 D/LeakCanary: │    Leaking: NO (RouteInfoFragment↓ is not leaking and a class is never leaking)
2020-05-13 17:57:32.914 D/LeakCanary: │    ↓ static ViewDataBinding.sReferenceQueue
2020-05-13 17:57:32.914 D/LeakCanary: ├─ java.lang.ref.ReferenceQueue instance
2020-05-13 17:57:32.914 D/LeakCanary: │    Leaking: NO (RouteInfoFragment↓ is not leaking)
2020-05-13 17:57:32.914 D/LeakCanary: │    ↓ ReferenceQueue.head
2020-05-13 17:57:32.914 D/LeakCanary: ├─ androidx.databinding.ViewDataBinding$WeakListener instance
2020-05-13 17:57:32.914 D/LeakCanary: │    Leaking: NO (RouteInfoFragment↓ is not leaking)
2020-05-13 17:57:32.914 D/LeakCanary: │    ↓ ViewDataBinding$WeakListener.mObservable
2020-05-13 17:57:32.914 D/LeakCanary: ├─ androidx.databinding.ViewDataBinding$LiveDataListener instance
2020-05-13 17:57:32.914 D/LeakCanary: │    Leaking: NO (RouteInfoFragment↓ is not leaking)
2020-05-13 17:57:32.914 D/LeakCanary: │    ↓ ViewDataBinding$LiveDataListener.mLifecycleOwner
2020-05-13 17:57:32.914 D/LeakCanary: ├─ iclaude.berlinwanderer.features.route.ui.route_dashboard.route_info.RouteInfoFragment instance
2020-05-13 17:57:32.915 D/LeakCanary: │    Leaking: NO (RouteDashboardFragment↓ is not leaking and Fragment#mFragmentManager is not null)
2020-05-13 17:57:32.915 D/LeakCanary: │    Fragment.mTag=f0
2020-05-13 17:57:32.915 D/LeakCanary: │    ↓ RouteInfoFragment.mParentFragment
2020-05-13 17:57:32.915 D/LeakCanary: ├─ iclaude.berlinwanderer.features.route.ui.route_dashboard.RouteDashboardFragment instance
2020-05-13 17:57:32.915 D/LeakCanary: │    Leaking: NO (Fragment#mFragmentManager is not null)
2020-05-13 17:57:32.915 D/LeakCanary: │    ↓ RouteDashboardFragment.mLifecycleRegistry
2020-05-13 17:57:32.915 D/LeakCanary: │                             ~~~~~~~~~~~~~~~~~~
2020-05-13 17:57:32.915 D/LeakCanary: ├─ androidx.lifecycle.LifecycleRegistry instance
2020-05-13 17:57:32.915 D/LeakCanary: │    Leaking: UNKNOWN
2020-05-13 17:57:32.915 D/LeakCanary: │    ↓ LifecycleRegistry.mObserverMap
2020-05-13 17:57:32.915 D/LeakCanary: │                        ~~~~~~~~~~~~
2020-05-13 17:57:32.915 D/LeakCanary: ├─ androidx.arch.core.internal.FastSafeIterableMap instance
2020-05-13 17:57:32.915 D/LeakCanary: │    Leaking: UNKNOWN
2020-05-13 17:57:32.915 D/LeakCanary: │    ↓ FastSafeIterableMap.mHashMap
2020-05-13 17:57:32.915 D/LeakCanary: │                          ~~~~~~~~
2020-05-13 17:57:32.915 D/LeakCanary: ├─ java.util.HashMap instance
2020-05-13 17:57:32.915 D/LeakCanary: │    Leaking: UNKNOWN
2020-05-13 17:57:32.915 D/LeakCanary: │    ↓ HashMap.table
2020-05-13 17:57:32.915 D/LeakCanary: │              ~~~~~
2020-05-13 17:57:32.915 D/LeakCanary: ├─ java.util.HashMap$Node[] array
2020-05-13 17:57:32.915 D/LeakCanary: │    Leaking: UNKNOWN
2020-05-13 17:57:32.915 D/LeakCanary: │    ↓ HashMap$Node[].[1]
2020-05-13 17:57:32.915 D/LeakCanary: │                     ~~~
2020-05-13 17:57:32.915 D/LeakCanary: ├─ java.util.HashMap$Node instance
2020-05-13 17:57:32.915 D/LeakCanary: │    Leaking: UNKNOWN
2020-05-13 17:57:32.915 D/LeakCanary: │    ↓ HashMap$Node.key
2020-05-13 17:57:32.915 D/LeakCanary: │                   ~~~
2020-05-13 17:57:32.915 D/LeakCanary: ├─ androidx.viewpager2.adapter.FragmentStateAdapter$5 instance
2020-05-13 17:57:32.915 D/LeakCanary: │    Leaking: UNKNOWN
2020-05-13 17:57:32.915 D/LeakCanary: │    Anonymous class implementing androidx.lifecycle.LifecycleEventObserver
2020-05-13 17:57:32.915 D/LeakCanary: │    ↓ FragmentStateAdapter$5.this$0
2020-05-13 17:57:32.916 D/LeakCanary: │                             ~~~~~~
2020-05-13 17:57:32.916 D/LeakCanary: ├─ iclaude.berlinwanderer.features.route.ui.route_dashboard.RouteDashboardViewPagerAdapter instance
2020-05-13 17:57:32.916 D/LeakCanary: │    Leaking: UNKNOWN
2020-05-13 17:57:32.916 D/LeakCanary: │    ↓ RouteDashboardViewPagerAdapter.mObservable
2020-05-13 17:57:32.916 D/LeakCanary: │                                     ~~~~~~~~~~~
2020-05-13 17:57:32.916 D/LeakCanary: ├─ androidx.recyclerview.widget.RecyclerView$AdapterDataObservable instance
2020-05-13 17:57:32.916 D/LeakCanary: │    Leaking: UNKNOWN
2020-05-13 17:57:32.916 D/LeakCanary: │    ↓ RecyclerView$AdapterDataObservable.mObservers
2020-05-13 17:57:32.916 D/LeakCanary: │                                         ~~~~~~~~~~
2020-05-13 17:57:32.916 D/LeakCanary: ├─ java.util.ArrayList instance
2020-05-13 17:57:32.916 D/LeakCanary: │    Leaking: UNKNOWN
2020-05-13 17:57:32.916 D/LeakCanary: │    ↓ ArrayList.elementData
2020-05-13 17:57:32.916 D/LeakCanary: │                ~~~~~~~~~~~
2020-05-13 17:57:32.916 D/LeakCanary: ├─ java.lang.Object[] array
2020-05-13 17:57:32.916 D/LeakCanary: │    Leaking: UNKNOWN
2020-05-13 17:57:32.916 D/LeakCanary: │    ↓ Object[].[0]
2020-05-13 17:57:32.916 D/LeakCanary: │               ~~~
2020-05-13 17:57:32.916 D/LeakCanary: ├─ com.google.android.material.tabs.TabLayoutMediator$PagerAdapterObserver instance
2020-05-13 17:57:32.916 D/LeakCanary: │    Leaking: UNKNOWN
2020-05-13 17:57:32.916 D/LeakCanary: │    ↓ TabLayoutMediator$PagerAdapterObserver.this$0
2020-05-13 17:57:32.916 D/LeakCanary: │                                             ~~~~~~
2020-05-13 17:57:32.916 D/LeakCanary: ├─ com.google.android.material.tabs.TabLayoutMediator instance
2020-05-13 17:57:32.916 D/LeakCanary: │    Leaking: UNKNOWN
2020-05-13 17:57:32.916 D/LeakCanary: │    ↓ TabLayoutMediator.tabLayout
2020-05-13 17:57:32.916 D/LeakCanary: │                        ~~~~~~~~~
2020-05-13 17:57:32.916 D/LeakCanary: ├─ com.google.android.material.tabs.TabLayout instance
2020-05-13 17:57:32.916 D/LeakCanary: │    Leaking: YES (View detached and has parent)
2020-05-13 17:57:32.916 D/LeakCanary: │    mContext instance of iclaude.berlinwanderer.features.route.ui.RouteActivity with mDestroyed = false
2020-05-13 17:57:32.916 D/LeakCanary: │    View#mParent is set
2020-05-13 17:57:32.916 D/LeakCanary: │    View#mAttachInfo is null (view detached)
2020-05-13 17:57:32.916 D/LeakCanary: │    View.mID = R.id.tab_layout
2020-05-13 17:57:32.916 D/LeakCanary: │    View.mWindowAttachCount = 1
2020-05-13 17:57:32.916 D/LeakCanary: │    ↓ TabLayout.mParent
2020-05-13 17:57:32.916 D/LeakCanary: ╰→ androidx.constraintlayout.motion.widget.MotionLayout instance
2020-05-13 17:57:32.916 D/LeakCanary: ?     Leaking: YES (ObjectWatcher was watching this because iclaude.berlinwanderer.features.route.ui.route_dashboard.RouteDashboardFragment received Fragment#onDestroyView() callback (references to its views should be cleared to prevent leaks))
2020-05-13 17:57:32.916 D/LeakCanary: ?     key = 9c28ffc6-b1ce-4316-b015-c4df278892a1
2020-05-13 17:57:32.916 D/LeakCanary: ?     watchDurationMillis = 36154
2020-05-13 17:57:32.916 D/LeakCanary: ?     retainedDurationMillis = 31130
2020-05-13 17:57:32.916 D/LeakCanary: ?     mContext instance of iclaude.berlinwanderer.features.route.ui.RouteActivity with mDestroyed = false
2020-05-13 17:57:32.917 D/LeakCanary: ?     View#mParent is null
2020-05-13 17:57:32.917 D/LeakCanary: ?     View#mAttachInfo is null (view detached)
2020-05-13 17:57:32.917 D/LeakCanary: ?     View.mID = R.id.ml_main
2020-05-13 17:57:32.917 D/LeakCanary: ?     View.mWindowAttachCount = 1

What's the problem? How to solve?

Answer 1

I think this is a bug, its listed on google.

https://issuetracker.google.com/issues/151212195 https://issuetracker.google.com/issues/154751401

There is a solution mentioned in the comments that seems to be working for me. Make your FragmentStateAdapter user the constructor

 public FragmentStateAdapter(@NonNull FragmentManager fragmentManager,
            @NonNull Lifecycle lifecycle) {

From your container fragment create the adapter as follows:

FragmentManager fm = getChildFragmentManager();
Lifecycle lifecycle = getViewLifecycleOwner().getLifecycle();
fragmentAdapter = new FragmentAdapter(fm, lifecycle);