Fragment似乎非常适合将UI逻辑分离成一些模块。但是与 ViewPager 一起使用它的生命周期仍然对我来说很模糊。所以需要大师们的建议！
编辑
见下面的愚蠢解决方案;-）
范围
Main activity有一个具有片段的 ViewPager 。这些片段可以针对其他（子主）活动实现略微不同的逻辑，因此通过回调接口在活动内部填充片段数据。第一次启动时一切正常，但是！...
问题
当活动重新创建时（例如在方向更改时）， ViewPager 的片段也会重新创建。代码（您将在下面找到）表示每次创建活动时，我都会尝试创建与片段相同的新的 ViewPager 片段适配器（也许这是问题），但FragmentManager已将所有这些片段存储在某个地方（在哪里？）并开始为这些片段启动重建机制。因此，重建机制使用我的回调接口调用 “旧” 片段的 onAttach，onCreateView等方法来通过Activity的实现方法启动数据。但是该方法指向了通过Activity的onCreate方法创建的新片段。
问题
也许我使用了错误的模式，但是即使是Android 3 Pro书中也没有太多关于它的内容。因此，请给我一个或两个建议，并指出如何正确地执行它。非常感谢！
代码
Main Activity
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<String, Fragment> screens = new LinkedHashMap<String, Fragment>();
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也被称为helper
public class BasePagerActivity extends FragmentActivity {
BasePagerAdapter mPagerAdapter;
ViewPager mPager;
}
适配器
public class BasePagerAdapter extends FragmentPagerAdapter implements TitleProvider {
private Map<String, Fragment> mScreens;
public BasePagerAdapter(Map<String, Fragment> 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
}
}
碎片
public class MessagesFragment extends ListFragment {
private boolean mIsLastMessages;
private List<Message> 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<Message>();
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
一个简单的解决方案是在宿主 Activity 的 onSaveInstanceState 方法中使用 putFragment 将碎片保存起来，在 onCreate 方法中使用 getFragment 获取它们。但我仍然有一种奇怪的感觉，似乎事情不应该这样做... 请参考下面的代码：
@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();
...
}