Android 添加到后台堆栈时如何维护片段状态

我写了一个虚拟活动，在两个片段之间切换.从FragmentA转到FragmentB时，FragmentA会添加到后堆栈中.然而，当我返回FragmentA(通过按back)时，一个全新的FragmentA被创建，它所处的状态消失了.我觉得我想要的东西和this个问题一样，但我提供了一个完整的代码示例来帮助解决这个问题:

public class FooActivity extends Activity {
  @Override public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    final FragmentTransaction transaction = getFragmentManager().beginTransaction();
    transaction.replace(android.R.id.content, new FragmentA());
    transaction.commit();
  }

  public void nextFragment() {
    final FragmentTransaction transaction = getFragmentManager().beginTransaction();
    transaction.replace(android.R.id.content, new FragmentB());
    transaction.addToBackStack(null);
    transaction.commit();
  }

  public static class FragmentA extends Fragment {
    @Override public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
      final View main = inflater.inflate(R.layout.main, container, false);
      main.findViewById(R.id.next_fragment_button).setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
          ((FooActivity) getActivity()).nextFragment();
        }
      });
      return main;
    }

    @Override public void onSaveInstanceState(Bundle outState) {
      super.onSaveInstanceState(outState);
      // Save some state!
    }
  }

  public static class FragmentB extends Fragment {
    @Override public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
      return inflater.inflate(R.layout.b, container, false);
    }
  }
}

添加了一些日志(log)消息后:

07-05 14:28:59.722 D/OMG     ( 1260): FooActivity.onCreate
07-05 14:28:59.742 D/OMG     ( 1260): FragmentA.onCreateView
07-05 14:28:59.742 D/OMG     ( 1260): FooActivity.onResume
<Tap Button on FragmentA>
07-05 14:29:12.842 D/OMG     ( 1260): FooActivity.nextFragment
07-05 14:29:12.852 D/OMG     ( 1260): FragmentB.onCreateView
<Tap 'Back'>
07-05 14:29:16.792 D/OMG     ( 1260): FragmentA.onCreateView

它永远不会调用FragmentA.onSaveInstanceState，当您回击时，它会创建一个新的Fragmenta.但是，如果我在Fragmenta上并锁定了屏幕，则确实会调用FragmentA.onSaveInstanceState.太奇怪了……我期望添加到后台堆栈的片段不需要重新创建，这是不是错了？以下是这docs人的评价:

然而，如果在删除片段时调用addToBackStack()，