ViewPager2中片段的复用

Question

我有片段 A 和 Viewpager2。在这个片段中，我创建了一个 B 片段列表以在 Viewpager2 中呈现。当我导航到另一个片段并返回到片段 A 时，我想为 Viewpager2 重新使用 B 片段列表，以避免重新创建同一片段（类型 B）的多个实例。但是我得到 IllegalStateException 异常，如下所示。

我该如何解决？

java.lang.IllegalStateException: Fragment already added
at androidx.fragment.app.Fragment.setInitialSavedState(Fragment.java:828)
at androidx.viewpager2.adapter.FragmentStateAdapter.ensureFragment(FragmentStateAdapter.java:277)
at androidx.viewpager2.adapter.FragmentStateAdapter.onBindViewHolder(FragmentStateAdapter.java:183)
at androidx.viewpager2.adapter.FragmentStateAdapter.onBindViewHolder(FragmentStateAdapter.java:72)
at androidx.recyclerview.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:7678)
at androidx.recyclerview.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:7761)
at androidx.recyclerview.widget.RecyclerView$Recycler.tryBindViewHolderByDeadline(RecyclerView.java:6582)
at androidx.recyclerview.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:6848)
at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6688)
at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6684)
at androidx.recyclerview.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2362)
at androidx.recyclerview.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1662)
at androidx.recyclerview.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1622)
at androidx.recyclerview.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:687)
at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:4604)
at androidx.recyclerview.widget.RecyclerView.onMeasure(RecyclerView.java:3981)
at android.view.View.measure(View.java:27124)
at android.view.ViewGroup.measureChild(ViewGroup.java:7951)
at androidx.viewpager2.widget.ViewPager2.onMeasure(ViewPager2.java:504)
at android.view.View.measure(View.java:27124)
at androidx.constraintlayout.widget.ConstraintLayout$Measurer.measure(ConstraintLayout.java:811)
at androidx.constraintlayout.core.widgets.ConstraintWidgetContainer.measure(ConstraintWidgetContainer.java:632)
at androidx.constraintlayout.core.widgets.ConstraintWidgetContainer.layout(ConstraintWidgetContainer.java:733)
at androidx.constraintlayout.core.widgets.analyzer.BasicMeasure.solveLinearSystem(BasicMeasure.java:160)
at androidx.constraintlayout.core.widgets.analyzer.BasicMeasure.solverMeasure(BasicMeasure.java:291)
at androidx.constraintlayout.core.widgets.ConstraintWidgetContainer.measure(ConstraintWidgetContainer.java:120)
at androidx.constraintlayout.widget.ConstraintLayout.resolveSystem(ConstraintLayout.java:1594)
at androidx.constraintlayout.widget.ConstraintLayout.onMeasure(ConstraintLayout.java:1708)
at android.view.View.measure(View.java:27124)
at androidx.swiperefreshlayout.widget.SwipeRefreshLayout.onMeasure(SwipeRefreshLayout.java:705)
at android.view.View.measure(View.java:27124)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:7980)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.view.View.measure(View.java:27124)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:995)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:721)
at android.view.View.measure(View.java:27124)
at androidx.drawerlayout.widget.DrawerLayout.onMeasure(DrawerLayout.java:1156)
at android.view.View.measure(View.java:27124)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:7980)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at androidx.appcompat.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:145)
at android.view.View.measure(View.java:27124)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:7980)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1552)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:842)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:721)
at android.view.View.measure(View.java:27124)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:7980)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.view.View.measure(View.java:27124)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:7980)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1552)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:842)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:721)
at android.view.View.measure(View.java:27124)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:7980)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at com.android.internal.policy.DecorView.onMeasure(DecorView.java:1248)
at android.view.View.measure(View.java:27124)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:4418)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:3123)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:3415)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:2819)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:10304)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:1063)
at android.view.Choreographer.doCallbacks(Choreographer.java:845)
at android.view.Choreographer.doFrame(Choreographer.java:780)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:1048)
at android.os.Handler.handleCallback(Handler.java:938)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loopOnce(Looper.java:226)
at android.os.Looper.loop(Looper.java:313)
at android.app.ActivityThread.main(ActivityThread.java:8582)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:563)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1133)

Answer 1

ViewPager2 自己记住你的片段，你不必在返回片段时添加它们。