java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法'java.lang.Object android.util.SparseArray.get（int）'

Question

当我第一次启动视图分页器片段时，一切正常，并且在视图分页器内部的片段之间导航正常.....当我打开另一个片段，然后回到具有viewpager的上一个片段时，就会发生问题，则会引发此错误

  

支持视图寻呼机的片段

public class ViewPagerAdapterFragment extends Fragment {


    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View view = inflater.inflate(R.layout.fragment_view_pager_adapter, container, false);

        ViewPager pager = view.findViewById(R.id.viewpager);

        setupViewPager(pager);
        return view;
    }

    private void setupViewPager(ViewPager viewPager) {
        ViewPagerAdapter adapter = new ViewPagerAdapter(getChildFragmentManager());
        adapter.addFragment(new  HomeFragment(), "Doadores");
        adapter.addFragment(new RequisitantesFragment(), "Requisitantes");
        viewPager.setAdapter(adapter);
    }
}

  

ViewPagerAdapter

public class ViewPagerAdapter extends FragmentStatePagerAdapter {

    private List<Fragment> mFragmentList= new ArrayList<>();
    private List<String> mFragmentTitleList = new ArrayList<>();

    public ViewPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        return mFragmentList.get(position);
    }

    @Override
    public int getCount() {
        return mFragmentList.size();
    }

    @Nullable
    @Override
    public CharSequence getPageTitle(int position) {
        return mFragmentTitleList.get(position);
    }

    public void addFragment(Fragment fragment, String title) {
        mFragmentList.add(fragment);
        mFragmentTitleList.add(title);
    }
}

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: mz.co.vida, PID: 22794
    java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object android.util.SparseArray.get(int)' on a null object reference
        at androidx.fragment.app.FragmentManagerImpl.getFragment(FragmentManager.java:936)
        at androidx.fragment.app.FragmentStatePagerAdapter.restoreState(FragmentStatePagerAdapter.java:217)
        at androidx.viewpager.widget.ViewPager.onRestoreInstanceState(ViewPager.java:1461)
        at android.view.View.dispatchRestoreInstanceState(View.java:14752)
        at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:3121)
        at android.view.View.restoreHierarchyState(View.java:14730)
        at androidx.fragment.app.Fragment.restoreViewState(Fragment.java:494)
        at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManager.java:1486)
        at androidx.fragment.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1784)
        at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManager.java:1852)
        at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:802)
        at androidx.fragment.app.FragmentManagerImpl.executeOps(FragmentManager.java:2625)
        at androidx.fragment.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2411)
        at androidx.fragment.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManager.java:2366)
        at androidx.fragment.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:2273)
        at androidx.fragment.app.FragmentManagerImpl$1.run(FragmentManager.java:733)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:148)
        at android.app.ActivityThread.main(ActivityThread.java:5417)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)