这个网上貌似很多回答，大多数是转载，监听onkeyDown消息没错，可是好多都没有给出获取当前音量的方法，基本上没法直接用。下面这个测试是有效的。
[java] view plaincopy
1.AudioManager audio = (AudioManager) getSystemService(Service.AUDIO_SERVICE);  
2.@Override  
3.public boolean onKeyDown(int keyCode, KeyEvent event) {  
4.   switch (keyCode) {  
5.   case KeyEvent.KEYCODE_VOLUME_UP:  
6.     audio.adjustStreamVolume(  
7.         AudioManager.STREAM_MUSIC,  
8.         AudioManager.ADJUST_RAISE, // 增加音量  
9.         AudioManager.FLAG_PLAY_SOUND | AudioManager.FLAG_SHOW_UI);  
10.     return true;  
11.    case KeyEvent.KEYCODE_VOLUME_DOWN:  
12.     audio.adjustStreamVolume(  
13.         AudioManager.STREAM_MUSIC,  
14.         AudioManager.ADJUST_LOWER,//减少音量  
15.         AudioManager.FLAG_PLAY_SOUND | AudioManager.FLAG_SHOW_UI);  
16.     return true;  
17.     default:  
18.     break;  
19.   }  
20.   return super.onKeyDown(keyCode, event);  
21.}