Android AudioManager获取媒体焦点

      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

package com.example.mediatest;

import java.io.IOException;

import android.app.Activity;
import android.content.BroadcastReceiver;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.content.res.AssetFileDescriptor;
import android.media.AudioManager;
import android.media.AudioManager.OnAudioFocusChangeListener;
import android.media.MediaPlayer;
import android.media.MediaPlayer.OnCompletionListener;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.Toast;

public class MainActivity extends Activity {

	private Button play;
	private Button stop;
	private AudioManager am;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		play = (Button) findViewById(R.id.button1);
		stop = (Button) findViewById(R.id.button2);
		am = (AudioManager) getSystemService(Context.AUDIO_SERVICE);
		initBeepSound();
		mode = am.getMode();
		if (mode == AudioManager.MODE_NORMAL) {
			Toast.makeText(this, "MODE_NORMAL", Toast.LENGTH_LONG).show();
		} else if (mode == AudioManager.MODE_IN_CALL) {
			Toast.makeText(this, "MODE_IN_CALL", Toast.LENGTH_LONG).show();

		} else if (mode == AudioManager.MODE_RINGTONE) {
			Toast.makeText(this, "MODE_RINGTONE", Toast.LENGTH_LONG).show();

		}
		remoteControlReceiver = new ComponentName(" com.example.mediatest",
				" com.example.mediatest.RemoteControlReceiver");
		play.setOnClickListener(new OnClickListener() {

			@Override
			public void onClick(View v) {
				if (mediaPlayer != null) {
					mediaPlayer.start();

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

		});
		stop.setOnClickListener(new OnClickListener() {

			@Override
			public void onClick(View v) {
				if (mediaPlayer != null && mediaPlayer.isPlaying()) {
					mediaPlayer.stop();
					mediaPlayer.release();
					mediaPlayer = null;
				}
				am.abandonAudioFocus(afChangeListener);
			}
		});
	}

	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();
				}

			}
		}
	};
	/**
	 * When the beep has finished playing, rewind to queue up another one.
	 */
	private final OnCompletionListener beepListener = new OnCompletionListener() {
		public void onCompletion(MediaPlayer mediaPlayer) {
			mediaPlayer.seekTo(0);
		}
	};
	private MediaPlayer mediaPlayer;
	private ComponentName remoteControlReceiver;
	private int mode;

	private void initBeepSound() {
		if (mediaPlayer == null) {
			// The volume on STREAM_SYSTEM is not adjustable, and users found it
			// too loud,
			// so we now play on the music stream.
			setVolumeControlStream(AudioManager.STREAM_MUSIC);
			mediaPlayer = new MediaPlayer();
			mediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);
			mediaPlayer.setOnCompletionListener(beepListener);

			AssetFileDescriptor file = getResources().openRawResourceFd(
					R.raw.demo);
			try {
				mediaPlayer.setDataSource(file.getFileDescriptor(),
						file.getStartOffset(), file.getLength());
				file.close();
				mediaPlayer.prepare();
			} catch (IOException e) {
				mediaPlayer = null;
			}
		}
	}

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

	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		// Inflate the menu; this adds items to the action bar if it is present.
		getMenuInflater().inflate(R.menu.main, menu);
		return true;
	}

}

下载 http://download.csdn.net/detail/chenchuntong/5268025