用导航组件导航替换片段后，片段内的 ViewPager2 泄漏

Question

起初，我在BottomNavigationView 和数据绑定的选项卡中遇到了ViewPager2 的问题，数据绑定也与ViewPager2 泄漏，应该在onDestroyView 中为空，泄漏并设法将问题缩小到ViewPager2 使用 findNavController().navigate 从包含 ViewPager2 的片段导航到另一个片段时。

它是这样发生的，它发生在我导航到另一个用 ViewPager2 替换当前片段的片段时。

这里是代码

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.fragment.app.FragmentContainerView
        android:id="@+id/nav_host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:defaultNavHost="true"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"

        app:layout_constraintTop_toTopOf="parent"
        app:navGraph="@navigation/nav_graph" />

</androidx.constraintlayout.widget.ConstraintLayout>

nav_graph.xml

<?xml version="1.0" encoding="utf-8"?>
<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/nav_graph_parent"
    app:startDestination="@id/parent_dest">

    <fragment
        android:id="@+id/parent_dest"
        android:name="com.smarttoolfactory.tutorial6_7navigationui_memoryleakcheck.viewpagerfragment.ViewPagerContainerFragment"
        android:label="MainFragment"
        tools:layout="@layout/fragment_viewpager_container">

        <!-- Login -->
        <action
            android:id="@+id/action_main_dest_to_loginFragment2"
            app:destination="@id/loginFragment2" />
    </fragment>

    <!-- Login -->
    <fragment
        android:id="@+id/loginFragment2"
        android:name="com.smarttoolfactory.tutorial6_7navigationui_memoryleakcheck.blankfragment.LoginFragment2"
        android:label="LoginFragment2"
        tools:layout="@layout/fragment_login2"/>

</navigation>

包含ViewPager2 和TabLayout 的片段

class ViewPagerContainerFragment : Fragment() {

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        return inflater.inflate(R.layout.fragment_viewpager_container, container, false)
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        // ViewPager2
        val viewPager = view.findViewById<ViewPager2>(R.id.viewPager)

        /*
            Set Adapter for ViewPager inside this fragment using this Fragment,
            more specifically childFragmentManager as param
         */
        viewPager.adapter = ChildFragmentStateAdapter(this)

        // TabLayout
        val tabLayout = view.findViewById<TabLayout>(R.id.tabLayout)

        // Bind tabs and viewpager
        TabLayoutMediator(tabLayout, viewPager) { tab, position ->
            when (position) {
                0 -> tab.text = "Home"
                1 -> tab.text = "Dashboard"
                2 -> tab.text = "Notification"
                3 -> tab.text = "Login"
            }
        }.attach()
    }
}

fragment_viewpager_container

<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.google.android.material.tabs.TabLayout
        android:id="@+id/tabLayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:tabMode="scrollable" />

    <androidx.viewpager2.widget.ViewPager2
        android:id="@+id/viewPager"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/tabLayout" />

</androidx.constraintlayout.widget.ConstraintLayout>

片段没有什么特别之处，但我添加了一种布局，也许 Material 小部件正在泄漏，我不知道

<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/fragment_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/colorHome1"
    android:padding="8dp">

    <com.google.android.material.textview.MaterialTextView
        android:id="@+id/tvTitle"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Home Fragment1"
        android:textColor="#fff"
        android:textSize="32sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.3" />

    <com.google.android.material.button.MaterialButton
        android:id="@+id/btnNextPage"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Next Page"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/tvTitle" />
    
</androidx.constraintlayout.widget.ConstraintLayout>

Leak Canary 的堆转储

┬───
│ GC Root: System class
│
├─ android.app.ActivityThread class
│    Leaking: NO (MainActivity↓ is not leaking and a class is never leaking)
│    ↓ static ActivityThread.sCurrentActivityThread
├─ android.app.ActivityThread instance
│    Leaking: NO (MainActivity↓ is not leaking)
│    ↓ ActivityThread.mTopActivityClient
├─ android.app.ActivityThread$ActivityClientRecord instance
│    Leaking: NO (MainActivity↓ is not leaking)
│    ↓ ActivityThread$ActivityClientRecord.activity
├─ com.smarttoolfactory.tutorial6_7navigationui_memoryleakcheck.MainActivity instance
│    Leaking: NO (NavHostFragment↓ is not leaking and Activity#mDestroyed is false)
│    ↓ MainActivity.mFragments
├─ androidx.fragment.app.FragmentController instance
│    Leaking: NO (NavHostFragment↓ is not leaking)
│    ↓ FragmentController.mHost
├─ androidx.fragment.app.FragmentActivity$HostCallbacks instance
│    Leaking: NO (NavHostFragment↓ is not leaking)
│    ↓ FragmentActivity$HostCallbacks.mFragmentManager
├─ androidx.fragment.app.FragmentManagerImpl instance
│    Leaking: NO (NavHostFragment↓ is not leaking)
│    ↓ FragmentManagerImpl.mPrimaryNav
├─ androidx.navigation.fragment.NavHostFragment instance
│    Leaking: NO (ViewPagerContainerFragment↓ is not leaking and Fragment#mFragmentManager is not null)
│    ↓ NavHostFragment.mChildFragmentManager
├─ androidx.fragment.app.FragmentManagerImpl instance
│    Leaking: NO (ViewPagerContainerFragment↓ is not leaking)
│    ↓ FragmentManagerImpl.mFragmentStore
├─ androidx.fragment.app.FragmentStore instance
│    Leaking: NO (ViewPagerContainerFragment↓ is not leaking)
│    ↓ FragmentStore.mActive
├─ java.util.HashMap instance
│    Leaking: NO (ViewPagerContainerFragment↓ is not leaking)
│    ↓ HashMap.table
├─ java.util.HashMap$Node[] array
│    Leaking: NO (ViewPagerContainerFragment↓ is not leaking)
│    ↓ HashMap$Node[].[0]
├─ java.util.HashMap$Node instance
│    Leaking: NO (ViewPagerContainerFragment↓ is not leaking)
│    ↓ HashMap$Node.value
├─ androidx.fragment.app.FragmentStateManager instance
│    Leaking: NO (ViewPagerContainerFragment↓ is not leaking)
│    ↓ FragmentStateManager.mFragment
├─ com.smarttoolfactory.tutorial6_7navigationui_memoryleakcheck.viewpagerfragment.ViewPagerContainerFragment instance
│    Leaking: NO (Fragment#mFragmentManager is not null)
│    ↓ ViewPagerContainerFragment.mLifecycleRegistry
│                                 ~~~~~~
├─ androidx.lifecycle.LifecycleRegistry instance
│    Leaking: UNKNOWN
│    ↓ LifecycleRegistry.mObserverMap
│                        ~~~~
├─ androidx.arch.core.internal.FastSafeIterableMap instance
│    Leaking: UNKNOWN
│    ↓ FastSafeIterableMap.mEnd
│                          ~~
├─ androidx.arch.core.internal.SafeIterableMap$Entry instance
│    Leaking: UNKNOWN
│    ↓ SafeIterableMap$Entry.mKey
│                            ~~
├─ androidx.viewpager2.adapter.FragmentStateAdapter$FragmentMaxLifecycleEnforcer$3 instance
│    Leaking: UNKNOWN
│    Anonymous class implementing androidx.lifecycle.LifecycleEventObserver
│    ↓ FragmentStateAdapter$FragmentMaxLifecycleEnforcer$3.this$1
│                                                          ~~
├─ androidx.viewpager2.adapter.FragmentStateAdapter$FragmentMaxLifecycleEnforcer instance
│    Leaking: UNKNOWN
│    ↓ FragmentStateAdapter$FragmentMaxLifecycleEnforcer.mViewPager
│                                                        ~~~~
├─ androidx.viewpager2.widget.ViewPager2 instance
│    Leaking: YES (View detached and has parent)
│    mContext instance of com.smarttoolfactory.tutorial6_7navigationui_memoryleakcheck.MainActivity with mDestroyed = false
│    View#mParent is set
│    View#mAttachInfo is null (view detached)
│    View.mID = R.id.viewPager
│    View.mWindowAttachCount = 1
│    ↓ ViewPager

如果您希望自己检查或重新创建问题，我还会添加 github link。

Answer 1

在片段的onDestroyView 方法中从ViewPager2 中移除适配器解决了FragmentStateAdapter 的内存泄漏问题

 override fun onDestroyView() {

        val viewPager2 = dataBinding?.viewPager

        viewPager2?.let {
            it.adapter = null
        }
        super.onDestroyView()
 }

还在片段的onDestroyView 中将数据绑定设置为空，我在基本片段中进行了设置，这导致了与数据绑定相关的内存泄漏。或者使用here 中提到的viewBinding，它适用于数据绑定。

private var _binding: ResultProfileBinding? = null
// This property is only valid between onCreateView and
// onDestroyView.
private val binding get() = _binding!!

override fun onCreateView(
    inflater: LayoutInflater,
    container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    _binding = ResultProfileBinding.inflate(inflater, container, false)
    val view = binding.root
    return view
}

override fun onDestroyView() {
    super.onDestroyView()
    _binding = null
} 

注意：片段比他们的观点更长寿。确保你清理任何 对片段中的绑定类实例的引用 onDestroyView() 方法。

防止在片段内使用ViewPager2 的内存泄漏的另一件事是使用viewLifeCycleOwner 的生命周期，它位于onCreateView 和onDestroyView 之间，而不是this 和FragmentStateAdapter 中提到的here。

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