AudioManager获取、释放媒体焦点

转载自：http://blog.csdn.net/chenchuntong/article/details/8813719

平时开发的时候 遇到这样的一个问题: 我开着系统的音乐播放器，我在我的应用程序里面播一段音乐 两个音乐会同时播放通过在stackoverflow查资料后才发行我们得自己音乐需要获取焦点，在我们音乐播完了以后释放掉焦点。这样系统的歌曲会继续播放下面介绍一下步骤

1.获取AudioManager对象

 AudioManager   am = (AudioManager) getSystemService(Context.AUDIO_SERVICE);

2. 注册OnAudioFocusChangeListener监听

 OnAudioFocusChangeListener afChangeListener = new OnAudioFocusChangeListener() {
  public void onAudioFocusChange(int focusChange) {
   if (focusChange == AudioManager.AUDIOFOCUS_LOSS_TRANSIENT) {
    if(mediaPlayer.isPlaying()){
     mediaPlayer.pause();
    }
    
   } else if (focusChange == AudioManager.AUDIOFOCUS_GAIN) {
    if(mediaPlayer==null){
     initBeepSound();
    }else if(!mediaPlayer.isPlaying()){
     
     mediaPlayer.start();
     
    }
    // Resume playback
   } else if (focusChange == AudioManager.AUDIOFOCUS_LOSS) {
    if(mediaPlayer.isPlaying()){
     
     mediaPlayer.stop();
    }
    am.abandonAudioFocus(afChangeListener);
    // Stop playback
   }else if(focusChange==AudioManager.AUDIOFOCUS_REQUEST_GRANTED){
    if (mediaPlayer.isPlaying()) {
     mediaPlayer.stop();
    }
    
   }else if(focusChange==AudioManager.AUDIOFOCUS_REQUEST_FAILED){
    if(mediaPlayer.isPlaying()){
     mediaPlayer.stop();
    }
    
   }
  }
 };
3.就是在我们播放音乐的时候为AudioManager添加获取焦点的监听

int result = am.requestAudioFocus(afChangeListener,
    // Use the music stream.
      AudioManager.STREAM_MUSIC, // Request permanent focus.
      AudioManager.AUDIOFOCUS_GAIN);
    if (result == AudioManager.AUDIOFOCUS_REQUEST_GRANTED) {
     mediaPlayer.start();
     // Start playback. // 开始播放音乐文件
    }

4.在我们不用的时候将焦点释放掉一般我们是在ondestroy()方法中释放

 @Override
 protected void onStop() {
  // TODO Auto-generated method stub
  super.onStop();
  am.abandonAudioFocus(afChangeListener);

 }

下面介绍一下AudioManager的几个常量

AUDIOFOCUS_REQUEST_GRANTED   永久获取媒体焦点（播放音乐）

AUDIOFOCUS_GAIN_TRANSIENT  暂时获取焦点 适用于短暂的音频

AUDIOFOCUS_GAIN_TRANSIENT_MAY_DUCK Duck我们应用跟其他应用共用焦点 我们播放的时候其他音频会降低音量

下面奉上代码

[java] view plaincopyprint?

1. package com.example.mediatest;  
2.   
3. import java.io.IOException;  
4.   
5. import android.app.Activity;  
6. import android.content.BroadcastReceiver;  
7. import android.content.ComponentName;  
8. import android.content.Context;  
9. import android.content.Intent;  
10. import android.content.res.AssetFileDescriptor;  
11. import android.media.AudioManager;  
12. import android.media.AudioManager.OnAudioFocusChangeListener;  
13. import android.media.MediaPlayer;  
14. import android.media.MediaPlayer.OnCompletionListener;  
15. import android.os.Bundle;  
16. import android.view.KeyEvent;  
17. import android.view.Menu;  
18. import android.view.View;  
19. import android.view.View.OnClickListener;  
20. import android.widget.Button;  
21. import android.widget.Toast;  
22.   
23. public class MainActivity extends Activity {  
24.   
25.     private Button play;  
26.     private Button stop;  
27.     private AudioManager am;  
28.     @Override  
29.     protected void onCreate(Bundle savedInstanceState) {  
30.         super.onCreate(savedInstanceState);  
31.         setContentView(R.layout.activity_main);  
32.         play = (Button) findViewById(R.id.button1);  
33.         stop = (Button) findViewById(R.id.button2);  
34.         am = (AudioManager) getSystemService(Context.AUDIO_SERVICE);  
35.         initBeepSound();  
36.         mode = am.getMode();  
37.         if (mode == AudioManager.MODE_NORMAL) {  
38.             Toast.makeText(this, "MODE_NORMAL", Toast.LENGTH_LONG).show();  
39.         } else if (mode == AudioManager.MODE_IN_CALL) {  
40.             Toast.makeText(this, "MODE_IN_CALL", Toast.LENGTH_LONG).show();  
41.   
42.         } else if (mode == AudioManager.MODE_RINGTONE) {  
43.             Toast.makeText(this, "MODE_RINGTONE", Toast.LENGTH_LONG).show();  
44.   
45.         }  
46.         remoteControlReceiver = new ComponentName(" com.example.mediatest",  
47.                 " com.example.mediatest.RemoteControlReceiver");  
48.         play.setOnClickListener(new OnClickListener() {  
49.   
50.             @Override  
51.             public void onClick(View v) {  
52.                 if (mediaPlayer != null) {  
53.                     mediaPlayer.start();  
54.   
55.                 } else {  
56.                     initBeepSound();  
57.                     mediaPlayer.start();  
58.                 }  
59.                 // Request audio focus for playback  
60.                 int result = am.requestAudioFocus(afChangeListener,  
61.                 // Use the music stream.  
62.                         AudioManager.STREAM_MUSIC, // Request permanent focus.  
63.                         AudioManager.AUDIOFOCUS_GAIN_TRANSIENT_MAY_DUCK);  
64.                 if (result == AudioManager.AUDIOFOCUS_REQUEST_GRANTED) {  
65.                     mediaPlayer.start();  
66.                     // Start playback. // 开始播放音乐文件  
67.                 }  
68.             }  
69.   
70.         });  
71.         stop.setOnClickListener(new OnClickListener() {  
72.   
73.             @Override  
74.             public void onClick(View v) {  
75.                 if (mediaPlayer != null && mediaPlayer.isPlaying()) {  
76.                     mediaPlayer.stop();  
77.                     mediaPlayer.release();  
78.                     mediaPlayer = null;  
79.                 }  
80.                 am.abandonAudioFocus(afChangeListener);  
81.             }  
82.         });  
83.     }  
84.   
85.     OnAudioFocusChangeListener afChangeListener = new OnAudioFocusChangeListener() {  
86.         public void onAudioFocusChange(int focusChange) {  
87.             if (focusChange == AudioManager.AUDIOFOCUS_LOSS_TRANSIENT) {  
88.                 if (mediaPlayer.isPlaying()) {  
89.                     mediaPlayer.pause();  
90.                 }  
91.   
92.             } else if (focusChange == AudioManager.AUDIOFOCUS_GAIN) {  
93.                 if (mediaPlayer == null) {  
94.                     initBeepSound();  
95.                 } else if (!mediaPlayer.isPlaying()) {  
96.   
97.                     mediaPlayer.start();  
98.   
99.                 }  
100.                 // Resume playback  
101.             } else if (focusChange == AudioManager.AUDIOFOCUS_LOSS) {  
102.                 if (mediaPlayer.isPlaying()) {  
103.   
104.                     mediaPlayer.stop();  
105.                 }  
106.                 am.abandonAudioFocus(afChangeListener);  
107.                 // Stop playback  
108.             } else if (focusChange == AudioManager.AUDIOFOCUS_REQUEST_GRANTED) {  
109.                 if (mediaPlayer.isPlaying()) {  
110.                     mediaPlayer.stop();  
111.                 }  
112.   
113.             } else if (focusChange == AudioManager.AUDIOFOCUS_REQUEST_FAILED) {  
114.                 if (mediaPlayer.isPlaying()) {  
115.                     mediaPlayer.stop();  
116.                 }  
117.   
118.             }  
119.         }  
120.     };  
121.     /** 
122.      * When the beep has finished playing, rewind to queue up another one. 
123.      */  
124.     private final OnCompletionListener beepListener = new OnCompletionListener() {  
125.         public void onCompletion(MediaPlayer mediaPlayer) {  
126.             mediaPlayer.seekTo(0);  
127.         }  
128.     };  
129.     private MediaPlayer mediaPlayer;  
130.     private ComponentName remoteControlReceiver;  
131.     private int mode;  
132.   
133.     private void initBeepSound() {  
134.         if (mediaPlayer == null) {  
135.             // The volume on STREAM_SYSTEM is not adjustable, and users found it  
136.             // too loud,  
137.             // so we now play on the music stream.  
138.             setVolumeControlStream(AudioManager.STREAM_MUSIC);  
139.             mediaPlayer = new MediaPlayer();  
140.             mediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);  
141.             mediaPlayer.setOnCompletionListener(beepListener);  
142.   
143.             AssetFileDescriptor file = getResources().openRawResourceFd(  
144.                     R.raw.demo);  
145.             try {  
146.                 mediaPlayer.setDataSource(file.getFileDescriptor(),  
147.                         file.getStartOffset(), file.getLength());  
148.                 file.close();  
149.                 mediaPlayer.prepare();  
150.             } catch (IOException e) {  
151.                 mediaPlayer = null;  
152.             }  
153.         }  
154.     }  
155.   
156.     @Override  
157.     protected void onStop() {  
158.         // TODO Auto-generated method stub  
159.         super.onStop();  
160.         am.abandonAudioFocus(afChangeListener);  
161.   
162.     }  
163.   
164.     @Override  
165.     public boolean onCreateOptionsMenu(Menu menu) {  
166.         // Inflate the menu; this adds items to the action bar if it is present.  
167.         getMenuInflater().inflate(R.menu.main, menu);  
168.         return true;  
169.     }  
170.   
171. }