Service Introduction
Service是android四大组件中与Activity最相似的组件,他们都可代表可执行的程序。Service与Activity
的区别在于:Service一直在后台运行,他没有用户界面,所以绝对不会到前台来,所以Service也有自己的
生命周期
About BroadcastReceiver
BroadcastReceiver也是安卓的四大组件之一,这种组件实际上就是一种全局的监听器,用于监听系统全局。
它属于系统级的监听器,它拥有自己进程,只要存在与之匹配的intent就会被激活。
Based on the music player of Service
Renderings:
1, an example configuration file AndroidManifest.xml Service
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.example.musicproject.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>
<service android:name=".MusicService">
</service>
</application>
2,MainActivity.java
package com.example.musicproject;
import android.app.Activity;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ImageButton;
import android.widget.TextView;
public class MainActivity extends Activity implements OnClickListener
{
// 获取界面中显示歌曲标题、作者文本框
TextView title, author;
// 播放/暂停、停止按钮
ImageButton play, stop;
ActivityReceiver activityReceiver;
public static final String CTL_ACTION =
"bzu.action.CTL_ACTION";
public static final String UPDATE_ACTION =
"bzu.action.UPDATE_ACTION";
// 定义音乐的播放状态,1代表没有播放;2代表正在播放;3代表暂停
int status = 1;
String[] titleStrs = new String[] { "平凡之路", "笑忘书", "走在冷风中" };
String[] authorStrs = new String[] { "朴树", "李荣浩", "刘思涵" };
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initView();
activityReceiver = new ActivityReceiver();
// 注册BroadcastReceiver
// 创建IntentFilter
IntentFilter filter = new IntentFilter();
// 指定BroadcastReceiver监听的Action
filter.addAction(UPDATE_ACTION);
registerReceiver(activityReceiver, filter);
// 启动后台Service
Intent intent = new Intent(this, MusicService.class);
startService(intent);
}
private void initView(){
// 获取程序界面界面中的两个按钮
play = (ImageButton) this.findViewById(R.id.play);
stop = (ImageButton) this.findViewById(R.id.stop);
title = (TextView) findViewById(R.id.title);
author = (TextView) findViewById(R.id.author);
// 为两个按钮的单击事件添加监听器
play.setOnClickListener(this);
stop.setOnClickListener(this);
}
// 自定义的BroadcastReceiver,负责监听从Service传回来的广播
public class ActivityReceiver extends BroadcastReceiver
{
@Override
public void onReceive(Context context, Intent intent)
{
// 获取Intent中的update消息,update代表播放状态
int update = intent.getIntExtra("update", -1);
// 获取Intent中的current消息,current代表当前正在播放的歌曲
int current = intent.getIntExtra("current", -1);
if (current >= 0){//设置信息
title.setText(titleStrs[current]);
author.setText(authorStrs[current]);
}
switch (update)
{
// 进入播放状态
case 1:
play.setImageResource(R.drawable.play);
status = 1;
break;
// 控制系统进入暂停状态
case 2:
// 播放状态下设置使用暂停图标
play.setImageResource(R.drawable.pause);
// 设置当前状态
status = 2;
break;
// 暂停状态下设置使用播放图标
case 3:
play.setImageResource(R.drawable.play);
// 设置当前状态
status = 3;
break;
}
}
}
@Override
public void onClick(View source)
{
// 创建Intent
Intent intent = new Intent("bzu.action.CTL_ACTION");
switch (source.getId())
{
// 按下播放/暂停按钮
case R.id.play:
intent.putExtra("control", 1);
break;
// 按下停止按钮
case R.id.stop:
intent.putExtra("control", 2);
break;
}
// 发送广播,将被Service组件中的BroadcastReceiver接收到
sendBroadcast(intent);
}
}
3,MusicService.java
/**
*
*/
package com.example.musicproject;
import java.io.IOException;
import android.app.Service;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.res.AssetFileDescriptor;
import android.content.res.AssetManager;
import android.media.MediaPlayer;
import android.media.MediaPlayer.OnCompletionListener;
import android.os.IBinder;
public class MusicService extends Service
{
//广播
MyReceiver serviceReceiver;
AssetManager am;
String[] musics = new String[] { "pfzl.mp3", "xws.mp3",
"zzlfz.mp3" };
MediaPlayer mPlayer;
// 当前的状态,1 代表没有播放 ;2代表 正在播放;3代表暂停
int status = 1;
// 记录当前正在播放的音乐
int current = 0;
@Override
public IBinder onBind(Intent intent)
{
return null;
}
@Override
public void onCreate()
{
am = getAssets();
// 创建BroadcastReceiver
serviceReceiver = new MyReceiver();
// 创建IntentFilter
IntentFilter filter = new IntentFilter();
filter.addAction(MainActivity.CTL_ACTION);
registerReceiver(serviceReceiver, filter);
// 创建MediaPlayer
mPlayer = new MediaPlayer();
// 为MediaPlayer播放完成事件绑定监听器
mPlayer.setOnCompletionListener(new OnCompletionListener() //①
{
@Override
public void onCompletion(MediaPlayer mp)
{
current++;
if (current >= 3)
{
current = 0;
}
// 发送广播通知Activity更改文本框
Intent sendIntent = new Intent(MainActivity.UPDATE_ACTION);
sendIntent.putExtra("current", current);
// 发送广播 ,将被Activity组件中的BroadcastReceiver接收到
sendBroadcast(sendIntent);
// 准备、并播放音乐
prepareAndPlay(musics[current]);
}
});
super.onCreate();
}
public class MyReceiver extends BroadcastReceiver
{
@Override
public void onReceive(final Context context, Intent intent)
{
//接收发送来的广播数据
int control = intent.getIntExtra("control", -1);
switch (control)
{
// 播放或暂停,判断上一次的状态
case 1:
// 原来处于没有播放状态
if (status == 1)
{
// 准备、并播放音乐
prepareAndPlay(musics[current]);
status = 2;
}
// 原来处于播放状态
else if (status == 2)
{
// 暂停
mPlayer.pause();
// 改变为暂停状态
status = 3;
}
// 原来处于暂停状态
else if (status == 3)
{
// 播放
mPlayer.start();
// 改变状态
status = 2;
}
break;
// 停止声音
case 2:
// 如果原来正在播放或暂停
if (status == 2 || status == 3)
{
// 停止播放
mPlayer.stop();
status = 1;
}
}
// 发送广播通知Activity更改图标、文本框
Intent sendIntent = new Intent(MainActivity.UPDATE_ACTION);
sendIntent.putExtra("update", status);
sendIntent.putExtra("current", current);
// 发送广播 ,将被Activity组件中的BroadcastReceiver接收到
sendBroadcast(sendIntent);
}
}
private void prepareAndPlay(String music)
{
try
{
// 打开指定音乐文件
AssetFileDescriptor afd = am.openFd(music);
mPlayer.reset();
// 使用MediaPlayer加载指定的声音文件。
mPlayer.setDataSource(afd.getFileDescriptor(),
afd.getStartOffset(), afd.getLength());
// 准备声音
mPlayer.prepare();
// 播放
mPlayer.start();
}
catch (IOException e)
{
e.printStackTrace();
}
}
}