ViewPager和fragments-存储fragment状态的正确方式是什么？

碎片似乎非常适合将UI逻辑分离成一些模块。但是与ViewPager一起使用时，它的生命周期对我来说仍然模糊不清。所以，我非常需要专家的意见！

编辑

请看下面的愚蠢解决方案；-）

范围

主活动有一个带有碎片的ViewPager。这些碎片可以为其他（子主要）活动实现略微不同的逻辑，因此通过活动内的回调接口填充碎片的数据。而且在第一次启动时一切都正常工作，但是！...

问题

当活动重新创建（例如方向更改）时，ViewPager的碎片也会重新创建。下面的代码（您将在下面找到）表示每次创建活动时，我都尝试创建一个与碎片相同的新的ViewPager碎片适配器（也许这就是问题所在），但是FragmentManager已经在某个地方存储了所有这些碎片（在哪里？）并且为这些碎片启动了重新创建机制。因此，重新创建机制调用了“旧”碎片的onAttach、onCreateView等方法，并通过活动的实现方法调用我的回调接口以初始化数据。但是，该方法指向通过活动的onCreate方法创建的新碎片。

问题

也许我使用了错误的模式，但是即使是《Android 3 Pro》书中也没有太多相关内容。所以，请给我一个或两个建议，指出如何正确地做。非常感谢！

代码

主活动

public class DashboardActivity extends BasePagerActivity implements OnMessageListActionListener {
private MessagesFragment mMessagesFragment;
@Override
protected void onCreate(Bundle savedInstanceState) {
    Logger.d("Dash onCreate");
    super.onCreate(savedInstanceState);
    setContentView(R.layout.viewpager_container);
    new DefaultToolbar(this);
    // create fragments to use
    mMessagesFragment = new MessagesFragment();
    mStreamsFragment = new StreamsFragment();
    // set titles and fragments for view pager
    Map screens = new LinkedHashMap();
    screens.put(getApplicationContext().getString(R.string.dashboard_title_dumb), new DumbFragment());
    screens.put(getApplicationContext().getString(R.string.dashboard_title_messages), mMessagesFragment);
    // instantiate view pager via adapter
    mPager = (ViewPager) findViewById(R.id.viewpager_pager);
    mPagerAdapter = new BasePagerAdapter(screens, getSupportFragmentManager());
    mPager.setAdapter(mPagerAdapter);
    // set title indicator
    TitlePageIndicator indicator = (TitlePageIndicator) findViewById(R.id.viewpager_titles);
    indicator.setViewPager(mPager, 1);
}
/* set of fragments callback interface implementations */
@Override
public void onMessageInitialisation() {
    Logger.d("Dash onMessageInitialisation");
    if (mMessagesFragment != null)
        mMessagesFragment.loadLastMessages();
}
@Override
public void onMessageSelected(Message selectedMessage) {
    Intent intent = new Intent(this, StreamActivity.class);
    intent.putExtra(Message.class.getName(), selectedMessage);
    startActivity(intent);
}

BasePagerActivity aka helper

public class BasePagerActivity extends FragmentActivity {
BasePagerAdapter mPagerAdapter;
ViewPager mPager;
}

Adapter

public class BasePagerAdapter extends FragmentPagerAdapter implements TitleProvider {
private Map mScreens;
public BasePagerAdapter(Map screenMap, FragmentManager fm) {
    super(fm);
    this.mScreens = screenMap;
}
@Override
public Fragment getItem(int position) {
    return mScreens.values().toArray(new Fragment[mScreens.size()])[position];
}
@Override
public int getCount() {
    return mScreens.size();
}
@Override
public String getTitle(int position) {
    return mScreens.keySet().toArray(new String[mScreens.size()])[position];
}
// hack. we don't want to destroy our fragments and re-initiate them after
@Override
public void destroyItem(View container, int position, Object object) {
    // TODO Auto-generated method stub
}
}

Fragment

public class MessagesFragment extends ListFragment {
private boolean mIsLastMessages;
private List mMessagesList;
private MessageArrayAdapter mAdapter;
private LoadMessagesTask mLoadMessagesTask;
private OnMessageListActionListener mListener;
// define callback interface
public interface OnMessageListActionListener {
    public void onMessageInitialisation();
    public void onMessageSelected(Message selectedMessage);
}
@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);
    // setting callback
    mListener = (OnMessageListActionListener) activity;
    mIsLastMessages = activity instanceof DashboardActivity;
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    inflater.inflate(R.layout.fragment_listview, container);
    mProgressView = inflater.inflate(R.layout.listrow_progress, null);
    mEmptyView = inflater.inflate(R.layout.fragment_nodata, null);
    return super.onCreateView(inflater, container, savedInstanceState);
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    // instantiate loading task
    mLoadMessagesTask = new LoadMessagesTask();
    // instantiate list of messages
    mMessagesList = new ArrayList();
    mAdapter = new MessageArrayAdapter(getActivity(), mMessagesList);
    setListAdapter(mAdapter);
}
@Override
public void onResume() {
    mListener.onMessageInitialisation();
    super.onResume();
}
public void onListItemClick(ListView l, View v, int position, long id) {
    Message selectedMessage = (Message) getListAdapter().getItem(position);
    mListener.onMessageSelected(selectedMessage);
    super.onListItemClick(l, v, position, id);
}
/* public methods to load messages from host acitivity, etc... */
}

解决方案

愚蠢的解决方案是在保存实例状态（宿主活动的onSaveInstanceState方法中）使用putFragment保存碎片，并在onCreate中使用getFragment获取它们。但是我仍然有一种奇怪的感觉，似乎事情不应该这样工作...请参见下面的代码：

    @Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    getSupportFragmentManager()
            .putFragment(outState, MessagesFragment.class.getName(), mMessagesFragment);
}
protected void onCreate(Bundle savedInstanceState) {
    Logger.d("Dash onCreate");
    super.onCreate(savedInstanceState);
    ...
    // create fragments to use
    if (savedInstanceState != null) {
        mMessagesFragment = (MessagesFragment) getSupportFragmentManager().getFragment(
                savedInstanceState, MessagesFragment.class.getName());
                StreamsFragment.class.getName());
    }
    if (mMessagesFragment == null)
        mMessagesFragment = new MessagesFragment();
    ...
}