Android FragmentManager保留了什么？

我有一个抽象基类，用于只实例化一个片段的活动：

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
         android:id="@+id/fragmentContainer" android:layout_width="match_parent" android:layout_height="match_parent" >
</FrameLayout>


public abstract class SingleFragmentActivity extends Activity {
    protected abstract Fragment createFragment();

    private Fragment m_fragment;
    public Fragment getSingleFragment() { return m_fragment; }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_fragment);

        FragmentManager fm = getFragmentManager();
        m_fragment = fm.findFragmentById( R.id.fragmentContainer );
        Log.d("SingleFragment", "fetching a fragment");
        if ( m_fragment == null ) {
            Log.d("SingleFragment", "SingleFragment requires creating a new one");
            m_fragment = createFragment();
            fm.beginTransaction().add( R.id.fragmentContainer, m_fragment ).commit();
        } else {
            Log.d("SingleFragment", "SingleFragment reusing one from fragment manager");
        }
    }
}

public class LoginActivity extends SingleFragmentActivity {
    private static final String TAG = "LOGIN ACTIVITY";

    private LoginFragment m_loginFragment;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        Log.d(TAG,"onCreate");
        super.onCreate(savedInstanceState);

        m_loginFragment = (LoginFragment) getSingleFragment();
        Log.d(TAG,"...login fragment foo = "+m_loginFragment.getFoo());
        m_loginFragment.setFoo( "Here's a new foo");
    }

    @Override
    public void onPause() { super.onPause(); Log.d(TAG,"onPause"); }

    @Override
    public void onDestroy() { super.onDestroy(); Log.d(TAG,"onDestroy"); }

    @Override
    public void onResume() { super.onResume(); Log.d(TAG,"onResume"); }


    @Override
    protected Fragment createFragment() {
        Log.d(TAG,"createFragment()");
        return new LoginFragment();
    }
}

public class LoginFragment extends Fragment {
    private static final String TAG = "LOGIN FRAGMENT";

    private String foo = "not set yet";
    public String getFoo() { return foo; }
    public void setFoo(String s) { foo = s; }

    @Override
    public void onCreate( Bundle savedInstanceState ) {
        super.onCreate(savedInstanceState);
        Log.d(TAG,"onCreate");
    }

    @Override
    public void onPause() { super.onPause(); Log.d(TAG,"onPause"); }

    @Override
    public void onDestroy() { super.onDestroy(); Log.d(TAG,"onDestroy"); }

    @Override
    public void onResume() { super.onResume(); Log.d(TAG,"onResume"); }
}

如果我运行此代码，并在手机启动后旋转手机，我会看到以下日志：

08-07 15:02:51.310: LOGIN ACTIVITY: onCreate
08-07 15:02:51.340: SingleFragment: fetching a fragment
08-07 15:02:51.340: SingleFragment: SingleFragment requires creating a new one
08-07 15:02:51.340: LOGIN ACTIVITY: createFragment()
08-07 15:02:51.340: LOGIN ACTIVITY: ...login fragment foo = not set yet
08-07 15:02:51.340: LOGIN FRAGMENT: onCreate
08-07 15:02:51.340: LOGIN ACTIVITY: onResume
08-07 15:02:51.340: LOGIN FRAGMENT: onResume
08-07 15:02:59.799: LOGIN FRAGMENT: onPause
08-07 15:02:59.799: LOGIN ACTIVITY: onPause
08-07 15:02:59.809: LOGIN FRAGMENT: onDestroy
08-07 15:02:59.809: LOGIN ACTIVITY: onDestroy
08-07 15:02:59.829: LOGIN ACTIVITY: onCreate
08-07 15:02:59.829: LOGIN FRAGMENT: onCreate
08-07 15:02:59.869: SingleFragment: fetching a fragment
08-07 15:02:59.869: SingleFragment: SingleFragment reusing one from fragment manager
08-07 15:02:59.869: LOGIN ACTIVITY: ...login fragment foo = not set yet
08-07 15:02:59.869: LOGIN ACTIVITY: onResume
08-07 15:02:59.869: LOGIN FRAGMENT: onResume

---

一切按预期进行：旋转手机会导致活动和碎片被破坏和重新创建；我看到碎片管理器恢复了一些东西，但我的问题是什么？成员变量foo未被保留，那么要还原的是什么？

Me也有同样的问题，并且在以前发布了一个问题-

当时的文件提到：

当配置更改导致承载这些配置的活动时 要重新启动，其新实例可能会使用不同的布局 不包含与上一个布局相同的片段。在这个 case之前的所有片段仍将被实例化并 在新实例中运行。然而，任何不再是 与视图层次结构中的标记关联的将不具有 内容视图已创建，并且将从isInLayout返回false。这个 这里的代码还显示了如何确定放置在 容器不再与该容器一起在布局中运行，并且 在这种情况下，请避免创建其视图层次结构

现在，该文档中不存在此部分

如果此片段已添加到布局中，则可以使用isInLayout进行检查