Android ViewPager2异常：java.lang.IllegalStateException:违反设计假设

我自己无法重现这个问题，但我在小米米9运行Android 10时注意到了这个问题。以下是我使用的

ViewPager2

和

RecyclerView

版本：

androidx.recyclerview:recyclerview:1.1.0 
androidx.viewpager2:viewpager2:1.0.0

这是stacktrace：

Fatal Exception: java.lang.IllegalStateException: Design assumption violated.
       at androidx.viewpager2.adapter.FragmentStateAdapter.placeFragmentInViewHolder(FragmentStateAdapter.java:287)
       at androidx.viewpager2.adapter.FragmentStateAdapter.onViewAttachedToWindow(FragmentStateAdapter.java:276)
       at androidx.viewpager2.adapter.FragmentStateAdapter.onViewAttachedToWindow(FragmentStateAdapter.java:67)
       at androidx.recyclerview.widget.RecyclerView.dispatchChildAttached(RecyclerView.java:7556)
       at androidx.recyclerview.widget.RecyclerView$5.addView(RecyclerView.java:860)
       at androidx.recyclerview.widget.ChildHelper.addView(ChildHelper.java:107)
       at androidx.recyclerview.widget.RecyclerView$LayoutManager.addViewInt(RecyclerView.java:8601)
       at androidx.recyclerview.widget.RecyclerView$LayoutManager.addView(RecyclerView.java:8559)
       at androidx.recyclerview.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1643)
       at androidx.recyclerview.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1587)
       at androidx.recyclerview.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:675)
       at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:4134)
       at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:3851)
       at androidx.recyclerview.widget.RecyclerView.onLayout(RecyclerView.java:4404)
       at android.view.View.layout(View.java:21963)
       at android.view.ViewGroup.layout(ViewGroup.java:6317)
       at androidx.viewpager2.widget.ViewPager2.onLayout(ViewPager2.java:527)
       at android.view.View.layout(View.java:21963)
       at android.view.ViewGroup.layout(ViewGroup.java:6317)
       at androidx.constraintlayout.widget.ConstraintLayout.onLayout(ConstraintLayout.java:1915)
       at android.view.View.layout(View.java:21963)
       at android.view.ViewGroup.layout(ViewGroup.java:6317)
       at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
       at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
       at android.view.View.layout(View.java:21963)
       at android.view.ViewGroup.layout(ViewGroup.java:6317)
       at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
       at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
       at android.view.View.layout(View.java:21963)
       at android.view.ViewGroup.layout(ViewGroup.java:6317)
       at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
       at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
       at android.view.View.layout(View.java:21963)
       at android.view.ViewGroup.layout(ViewGroup.java:6317)
       at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1829)
       at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1673)
       at android.widget.LinearLayout.onLayout(LinearLayout.java:1582)
       at android.view.View.layout(View.java:21963)
       at android.view.ViewGroup.layout(ViewGroup.java:6317)
       at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
       at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
       at com.android.internal.policy.DecorView.onLayout(DecorView.java:803)
       at android.view.View.layout(View.java:21963)
       at android.view.ViewGroup.layout(ViewGroup.java:6317)
       at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:3144)
       at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2654)
       at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1782)
       at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:7785)
       at android.view.Choreographer$CallbackRecord.run(Choreographer.java:1031)
       at android.view.Choreographer.doCallbacks(Choreographer.java:854)
       at android.view.Choreographer.doFrame(Choreographer.java:789)
       at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:1016)
       at android.os.Handler.handleCallback(Handler.java:883)
       at android.os.Handler.dispatchMessage(Handler.java:100)
       at android.os.Looper.loop(Looper.java:224)
       at android.app.ActivityThread.main(ActivityThread.java:7520)
       at java.lang.reflect.Method.invoke(Method.java)
       at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:539)
       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950)

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我不确定这是从我的代码触发的，因为stacktrace不是很清楚。另外，根据GoogleIssueTracker的说法，这个问题已经在viewpager2:1.0.0-beta03:中通过提交解决了，但在我的例子中并不是这样。这是另一篇关于同样问题的帖子，没有多少有用的答案：。如果有人知道为什么会发生这种情况或者如何解决，那就太好了

为了解决这个问题，我尽了一切努力，但都没有成功。我删除了fragmentStateAdapter中的getItemId，现在它可以正常工作。

如果您覆盖

getItemId（）

请确保您也覆盖

ContaineSitem（）

这里解释了对我有效的快速解决方法：