10-15 15:52:00.094 3808 3808 E AndroidRuntime: FATAL EXCEPTION: main
10-15 15:52:00.094 3808 3808 E AndroidRuntime: Process: com.xxxx.xxx, PID: 3808
10-15 15:52:00.094 3808 3808 E AndroidRuntime: java.lang.IllegalStateException: Fragment already added
10-15 15:52:00.094 3808 3808 E AndroidRuntime: at androidx.fragment.app.Fragment.setInitialSavedState(Fragment.java:679)
10-15 15:52:00.094 3808 3808 E AndroidRuntime: at androidx.viewpager2.adapter.FragmentStateAdapter.ensureFragment(FragmentStateAdapter.java:269)
10-15 15:52:00.094 3808 3808 E AndroidRuntime: at androidx.viewpager2.adapter.FragmentStateAdapter.onBindViewHolder(FragmentStateAdapter.java:175)
10-15 15:52:00.094 3808 3808 E AndroidRuntime: at androidx.viewpager2.adapter.FragmentStateAdapter.onBindViewHolder(FragmentStateAdapter.java:67)
10-15 15:52:00.094 3808 3808 E AndroidRuntime: at androidx.recyclerview.widget.RecyclerView
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Adapter.onBindViewHolder(RecyclerView.java:7065) 10-15 15:52:00.094 3808 3808 E AndroidRuntime: at androidx.recyclerview.widget.RecyclerView
Adapter.onBindViewHolder(RecyclerView.java:7065)10−1515:52:00.09438083808EAndroidRuntime:atandroidx.recyclerview.widget.RecyclerViewAdapter.bindViewHolder(RecyclerView.java:7107)
10-15 15:52:00.094 3808 3808 E AndroidRuntime: at androidx.recyclerview.widget.RecyclerView
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Recycler.tryBindViewHolderByDeadline(RecyclerView.java:6012) 10-15 15:52:00.094 3808 3808 E AndroidRuntime: at androidx.recyclerview.widget.RecyclerView
Recycler.tryBindViewHolderByDeadline(RecyclerView.java:6012)10−1515:52:00.09438083808EAndroidRuntime:atandroidx.recyclerview.widget.RecyclerViewRecycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:6279)
10-15 15:52:00.094 3808 3808 E AndroidRuntime: at androidx.recyclerview.widget.GapWorker.prefetchPositionWithDeadline(GapWorker.java:288)
10-15 15:52:00.094 3808 3808 E AndroidRuntime: at androidx.recyclerview.widget.GapWorker.flushTaskWithDeadline(GapWorker.java:345)
10-15 15:52:00.094 3808 3808 E AndroidRuntime: at androidx.recyclerview.widget.GapWorker.flushTasksWithDeadline(GapWorker.java:361)
10-15 15:52:00.094 3808 3808 E AndroidRuntime: at androidx.recyclerview.widget.GapWorker.prefetch(GapWorker.java:368)
10-15 15:52:00.094 3808 3808 E AndroidRuntime: at androidx.recyclerview.widget.GapWorker.run(GapWorker.java:399)
10-15 15:52:00.094 3808 3808 E AndroidRuntime: at android.os.Handler.handleCallback(Handler.java:755)
10-15 15:52:00.094 3808 3808 E AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:95)
10-15 15:52:00.094 3808 3808 E AndroidRuntime: at android.os.Looper.loop(Looper.java:154)
10-15 15:52:00.094 3808 3808 E AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:6141)
10-15 15:52:00.094 3808 3808 E AndroidRuntime: at java.lang.reflect.Method.invoke(Native Method)
10-15 15:52:00.094 3808 3808 E AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:913)
10-15 15:52:00.094 3808 3808 E AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:803)
报错AndroidRuntime: at androidx.fragment.app.Fragment.setInitialSavedState(Fragment.java:679)
这个错误是我从 fragment A 切换到 fragment B ,
fragment B再切换到 fragment C 中，
再切换到 fragment B中， fragment B 里面 使用了ViewPager2 + FragmentStateAdapter + RadioButton切换主题，问题就出在我使用的ViewPager2 + FragmentStateAdapter这里。
每次我在多个fragmentA,B,C之间多次切换后，切换到fragment B，点击 radioButton 通知ViewPager2 切换 fragment的主题时,使用方法viewPager2.setCurrentItem(index);，就报上面的错误。
我在想，是否是滑动效果的问题，于是 用
viewPager2.setCurrentItem(index,false);然后，由于viewpager2 里面的fragment 里面有recycleviewer ,把viewpager2 的宽高 固定 ，问题解决。
总结：1，viewPager2.setCurrentItem(index)改成viewPager2.setCurrentItem(index,false);
2，viewPager2 在布局文件里面把宽高 固定。
