我编写了一个在两个片段之间切换的虚拟活动。当您从 FragmentA 转到 FragmentB 时，FragmentA 被添加到后堆栈。但是，当我返回
FragmentA（通过按回）时，会创建一个全新的
FragmentA，并且它所处的状态会丢失。我已经包含了一个完整的代码示例来帮助根除这个问题：

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);
    }
  }
}

添加了一些日志消息：

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

它从不调用 FragmentA.onSaveInstanceState 并且在您回击时创建一个新的 FragmentA。但是，如果我在 FragmentA
上并锁定屏幕，则会调用
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是错误的吗？这是文档所说的：

然而，如果您在删除片段时确实调用了 addToBackStack()，那么片段将停止，并且如果用户导航回来，它将恢复。