防止在设备旋转时重新创建Android片段
问题：
当我旋转设备时，我的应用程序中的片段中包含的信息将被重新加载。 由于这个应用程序从互联网上提取信息，这意味着在重新收集数据的同时缺乏数据。
我试过的：
我已经阅读了许多文章和S / O问题，这些问题提供了一些通用指针，并尝试了他们的解决方案，从android:configChanges="orientation|screenSize"添加setRetainInstance(true); 在我的MainActivity和FragmentActivity 。 这些都没有阻止我的片段重新加载。 我在应用程序中的另一个活动中使用了android:configChanges （一个详细活动，当用户选择新闻故事时激活）并且它在那里正常工作，防止活动重新加载。
我的应用程序的结构：
这是一个简单的应用程序，它从“黑客新闻”API中提取数据并将其显示给用户。 有一个NavigationDrawer供用户选择不同的新闻类型。 NavigationDrawer中的每个项目都是在MainActivity.class中加载的不同Fragment。 这里HomeFragment.class的片段是HomeFragment.class ，它载有主要新闻故事。
我为什么在这里问：
我似乎无法找到任何与我目前的应用程序结构一致的东西，所以我想帮助找到解决这个看似微不足道（但令人困惑）问题的解决方案。
码：
MainActivity.java
package com.material.tdapps.hackernews.activity; import android.os.Bundle; import android.support.v4.app.Fragment; import android.support.v4.app.FragmentManager; import android.support.v4.app.FragmentTransaction; import android.support.v4.widget.DrawerLayout; import android.support.v7.app.AppCompatActivity; import android.support.v7.widget.Toolbar; import android.view.Menu; import android.view.MenuItem; import android.view.View; import com.material.tdapps.hackernews.R; public class MainActivity extends AppCompatActivity implements FragmentDrawer.FragmentDrawerListener { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); Toolbar appToolbar = (Toolbar) findViewById(R.id.toolbar); setSupportActionBar(appToolbar); //noinspection ConstantConditions getSupportActionBar().setDisplayShowHomeEnabled(true); FragmentDrawer drawerFragment = (FragmentDrawer) getSupportFragmentManager().findFragmentById(R.id.fragment_navigation_drawer); drawerFragment.setUp(R.id.fragment_navigation_drawer, (DrawerLayout) findViewById(R.id.drawer_layout), appToolbar); drawerFragment.setDrawerListener(this); displayView(0); } @Override public boolean onCreateOptionsMenu(Menu menu) { getMenuInflater().inflate(R.menu.menu_main, menu); return true; } @Override public boolean onOptionsItemSelected(MenuItem item) { int id = item.getItemId(); return id == R.id.action_settings || super.onOptionsItemSelected(item); } @Override public void onDrawerItemSelected(View view, int position) { displayView(position); } private void displayView(int position){ Fragment fragment = null; String title = getString(R.string.app_name); switch (position) { case 0: fragment = new HomeFragment(); title = getString(R.string.title_news); break; case 1: fragment = new ShowFragment(); title = getString(R.string.title_show); break; case 2: fragment = new AskFragment(); title = getString(R.string.title_ask); break; case 3: fragment = new JobsFragment(); title = getString(R.string.title_job); break; default: break; } if (fragment != null){ FragmentManager fragmentManager = getSupportFragmentManager(); FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction(); fragmentTransaction.replace(R.id.container_body, fragment); fragmentTransaction.commit(); getSupportActionBar().setTitle(title); } } }
HomeFragment.java
package com.material.tdapps.hackernews.activity; import android.app.Activity; import android.content.Context; import android.content.Intent; import android.os.AsyncTask; import android.os.Bundle; import android.support.annotation.Nullable; import android.support.v4.app.Fragment; import android.util.Log; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.BaseAdapter; import android.widget.Button; import android.widget.ImageButton; import android.widget.ListView; import android.widget.RelativeLayout; import android.widget.TextView; import com.material.tdapps.hackernews.JSON.JSONNewsParser; import com.material.tdapps.hackernews.R; import com.material.tdapps.hackernews.model.StoryFeed; import com.material.tdapps.hackernews.model.StoryItem; import java.net.MalformedURLException; public class HomeFragment extends Fragment { StoryFeed storyFeed; Context context; ListView listView; NewsListAdapter newsListAdapter; public HomeFragment() { } @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); } @Nullable @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { View rootView = inflater.inflate(R.layout.fragment_home, container, false); setRetainInstance(true); context = this.getActivity(); storyFeed = new StoryFeed(); newsListAdapter = new NewsListAdapter(this); listView = (ListView) rootView.findViewById(R.id.newsListView); if (savedInstanceState != null && (savedInstanceState.getSerializable("previousFeed") != null)) { Log.e("NOTIFY >> ", "GOING TO BUNDLE"); storyFeed = (StoryFeed)savedInstanceState.getSerializable("previousFeed"); listView.setAdapter(newsListAdapter); newsListAdapter.notifyDataSetChanged(); } else { Log.e("NOTIFY >> ", "GOING TO ASYNCTASK"); new AsyncLoadNewsFeed().execute(); listView.setAdapter(newsListAdapter); } setRetainInstance(true); return rootView; } @Override public void onAttach(Activity activity) { super.onAttach(activity); } @Override public void onDetach() { super.onDetach(); } private class AsyncLoadNewsFeed extends AsyncTask { @Override protected Void doInBackground(Void... params) { JSONNewsParser newsParser = new JSONNewsParser(); storyFeed = newsParser.parseJSON("https://hacker-news.firebaseio.com/v0/topstories.json",0,30); return null; } @Override protected void onPostExecute(Void aVoid) { super.onPostExecute(aVoid); if (storyFeed == null || storyFeed.getStoryCount() == 0){ StoryItem nullStoryItem = new StoryItem(); nullStoryItem.setTitle("ERROR: Null error!"); nullStoryItem.setNumberComments(0); nullStoryItem.setScore(0); nullStoryItem.setBodyText("NULL"); nullStoryItem.setTime(0); nullStoryItem.setAuthor("NULL"); nullStoryItem.setUrl("http://www.google.com"); storyFeed.addStory(nullStoryItem); } newsListAdapter.notifyDataSetChanged(); } } class NewsListAdapter extends BaseAdapter { private LayoutInflater layoutInflater; public NewsListAdapter(HomeFragment homeFragment){ layoutInflater = (LayoutInflater) homeFragment.getActivity().getSystemService(Context.LAYOUT_INFLATER_SERVICE); } @Override public int getCount() { return storyFeed.getStoryCount(); } @Override public Object getItem(int position) { return position; } @Override public long getItemId(int position) { return position; } class listViewHolder { TextView titleTxtV; TextView timeTxtV; TextView scoreTxtV; TextView authorTxtV; TextView domTxtV; Button commentB; RelativeLayout detailsLayout; listViewHolder(View v) { titleTxtV = (TextView) v.findViewById(R.id.titleText); timeTxtV = (TextView) v.findViewById(R.id.timeText); scoreTxtV = (TextView) v.findViewById(R.id.pointsText); authorTxtV = (TextView) v.findViewById(R.id.authorText); domTxtV = (TextView) v.findViewById(R.id.domainText); commentB = (Button) v.findViewById(R.id.commentButton); detailsLayout = (RelativeLayout) v.findViewById(R.id.newsDetailRelLayout); } } @Override public View getView(final int position, View convertView, ViewGroup parent) { View listItem = convertView; listViewHolder holder; if (listItem == null) { listItem = layoutInflater.inflate(R.layout.news_item_layout, parent, false ); holder = new listViewHolder(listItem); listItem.setTag(holder); } else { holder = (listViewHolder) listItem.getTag(); } holder.titleTxtV.setText(storyFeed.getStory(position).getTitle()); holder.timeTxtV.setText("Posted " + storyFeed.getStory(position).getTime()); holder.authorTxtV.setText(" By " + storyFeed.getStory(position).getAuthor()); holder.scoreTxtV.setText(storyFeed.getStory(position).getScore() + " Points "); holder.commentB.setText(Integer.toString(storyFeed.getStory(position).getNumberComments())); try { holder.domTxtV.setText("(" + storyFeed.getStory(position).getURLDomain() + ")"); } catch (MalformedURLException e) { e.printStackTrace(); } holder.commentB.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Intent showComments = new Intent(getActivity(), CommentActivity.class); getActivity().startActivity(showComments); } }); holder.detailsLayout.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Intent showDetails = new Intent(getActivity(), DetailWebActivity.class); Bundle detailsBundle = new Bundle(); //detailsBundle.putSerializable("newsFeed", storyFeed); showDetails.putExtra("news",storyFeed); showDetails.putExtras(detailsBundle); showDetails.putExtra("position", position); getActivity().startActivity(showDetails); } }); return listItem; } } }
AndroidManifest.xml中
调用setRetainInstance(true)将阻止重新创建Fragment 。 但是，现在Activity 始终重新创建DrawerFragment并强制重新创建HomeFragment ，从而导致您看到的行为。 在Activity.onCreate()检查savedInstanceState为null 。 如果是，请创建Fragment 。 如果没有，那么请不要因为系统会自动恢复它们。
您始终在displayView方法中创建一个新的Fragment 。 相反，您应该使用FragmentManager通过Id或Tag查找片段，然后将其放在容器视图中。
请参阅http://developer.android.com/reference/android/app/FragmentManager.html#findFragmentByTag(java.lang.String）
编辑
实际上@Larry Schiefer是对的，你甚至不需要找到一个片段，只需检查已保存的实例状态是否为null。