ViewPager和片段-什么是存储片段状态的正确方式?
片段似乎非常适合将UI逻辑分离到一些模块中。但是和ViewPager一样，它的生命周期对我来说仍然很模糊。所以我们非常需要大师的思想!
编辑
参见下面的哑巴解决方案;-)
范围
Main活动有一个带有片段的ViewPager。这些片段可以为其他(子主)活动实现稍微不同的逻辑，因此片段的数据是通过活动内部的回调接口填充的。第一次发射时一切正常，但是……
问题
当活动被重新创建时(例如在方向改变时)，ViewPager的片段也会被重新创建。代码(你会在下面发现)说，每次创建活动，我尝试创建一个新的ViewPager片段适配器相同的片段(也许这是问题)，但FragmentManager已经有所有这些片段存储在某个地方(哪里?)，并开始为那些重建机制。因此，重建机制调用“旧”片段的onAttach, onCreateView等与我的回调接口调用，通过活动的实现方法来初始化数据。但是这个方法指向通过Activity的onCreate方法创建的新创建的片段。
问题
也许我使用了错误的模式，但即使是Android 3 Pro书也没有太多关于它的内容。所以，请，给我一拳两拳，并指出如何做正确的方式。很多谢谢!
代码
主要活动
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<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又名助手
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
}
}
片段
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
愚蠢的解决方案是将碎片保存在onSaveInstanceState(主机活动)与putFragment和获得他们在onCreate通过getFragment。但我仍然有一种奇怪的感觉，事情不应该这样发展……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();
...
}
最佳答案