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?

Hypodermis

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);

Boesch

This is the best solution so far. Best practice would still indicate calling detach() on the TabLayoutMediator, perhaps in onDestroyView() of the Fragment, however there should be no need to null instances manually which this solutions avoids. – Rugger

I've been using FragmentStateAdapter(Fragment fragment) constructor, which in turn calls the constructor you've mentioned. But the important distinction is that it is called with fragment's lifecycle, not view's lifecycle. After explicitly passing viewLifecycleOwner instead the leak disappeared for me. – Durer

Does this only happens when using Fragment or even with Activity? – Elgon

Answer 2

You need to detach and set mediator to null in onDestroyView:

class YourFragment: Fragment() {
    
    private var mediator: TabLayoutMediator? = null

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        mediator = TabLayoutMediator(binding.tabLayout, binding.viewPager) { tab, position ->
            tab.setIcon(getTabIcon(position))
            tab.text = getTabTitle(position)
        }
        mediator.attach()
    }

    override fun onDestroyView() {
        super.onDestroyView()
        mediator?.detach()
        mediator = null
        binding.viewpager.adapter = null
        _binding = null
    }

}

Hoxsie

Answer 3

I had the same similar problem, you need to set the viewPager adapter to null inside onDestroyView , then possible if you are using databinding make sure u set the binding to null. Goodluck

Gastrology

I found a solution. It seems that in onDestroyView you have to set to null the viewpager.adaper field, the adapter itself, the TabLauoutMediator (after detaching it) and the binding class reference. I hope the official documentation becomes more clear in the future. – Hypodermis

Answer 4

Your mContext, being exposed by RouteActivity is lingering around even after RouteActivity is destroyed (or recreated). This is happening probably because something is using it. Track what is using mContext and stop that.

Atomize

RouteActivity is the Activity holding the Fragments, so it's not destroyed or recreated. – Hypodermis