防止在设备旋转时重新创建Android片段 [英] Prevent Android Fragment from Being Recreated on Device Rotate
问题描述
旋转设备时，包含在我的应用程序片段中的信息会重新加载.由于此应用程序从互联网上提取信息，因此，在收集数据的过程中，一段时间内缺少数据.
When I rotate my device, the information contained within my fragment in my app is reloaded. Since this app pulls information from the internet, this means, a lack of data for some time while data is being recollected.
从清单中的android:configChanges="orientation|screenSize"到在我的MainActivity和FragmentActivity中添加setRetainInstance(true);，我已经阅读了许多文章和S/O问题，给出了一些一般性的指针并尝试了它们的解决方案.这些都不起作用，无法重新加载我的片段.我在应用程序的另一个活动(详细活动，当用户选择新闻报道时会激活)中使用android:configChanges，并且该功能在该处正常工作，从而阻止了该活动的重新加载.
I have read many articles and S/O questions that give a few general pointers and have tried their solutions, from android:configChanges="orientation|screenSize" in the manifest to adding setRetainInstance(true); in both my MainActivity and FragmentActivity. Neither of these have worked to keep my fragment from reloading. I used the android:configChanges in another activity in the app (A detail activity, which activates when a user selects a news story) and it works properly there, preventing the activity from reloading.
这是一个简单的应用程序，可从"Hacker News" 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中的每个项目都是加载在MainActivity.class中的不同片段.这里要讨论的片段是HomeFragment.class，它加载了主要新闻报道.
This is a simple app that pulls data from the "Hacker News" API and shows it to the user. There is a NavigationDrawer for the user to select different news types. Each item in the NavigationDrawer is a different Fragment that loads in the MainActivity.class. The Fragment in question here is HomeFragment.class which loads the main news stories.
我目前似乎找不到与我的应用程序结构相适应的任何内容，因此我想寻求一些帮助，以寻求针对此看似微妙(但令人困惑)的问题的解决方案.
I can't seem to find anything that works with the structure of my app as it currently stands, so I would like some help in trying to find a solution for this seemingly trivial (but confusing) problem.
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<Void, Void, Void> {
@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
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.material.tdapps.hackernews" >
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.CHANGE_NETWORK_STATE" />
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:theme="@style/HackerNewsTheme" >
<activity
android:name=".activity.MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".activity.CommentActivity"
android:label="@string/title_activity_comment"
android:parentActivityName=".activity.MainActivity"
android:configChanges="orientation|screenSize">
<meta-data
android:name="android.support.PARENT_ACTIVITY"
android:value="com.material.tdapps.hackernews.activity.MainActivity" />
</activity>
<activity
android:name=".activity.DetailWebActivity"
android:label="@string/title_activity_detail_web"
android:parentActivityName=".activity.MainActivity"
android:configChanges="orientation|screenSize">
<meta-data
android:name="android.support.PARENT_ACTIVITY"
android:value="com.material.tdapps.hackernews.activity.MainActivity" />
</activity>
</application>
</manifest>
推荐答案
调用setRetainInstance(true)将阻止重新创建Fragment.但是，现在Activity总是 重新创建DrawerFragment并强行重新创建HomeFragment，从而导致您看到的行为.在您的Activity.onCreate()中，检查savedInstanceState是null.如果是，请创建您的Fragment.如果没有，请不要这样做，因为系统会自动还原它们.
Calling setRetainInstance(true) will prevent the Fragment from being re-created. But, right now the Activity is always re-creating the DrawerFragment and forcefully re-creating the HomeFragment, resulting in the behavior you are seeing. In your Activity.onCreate() check the savedInstanceState is null. If it is, create your Fragments. If not, then don't as the system will automatically restore them.
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