音频焦点系列：手写一个demo理解音频焦点与AudioMananger

先看测试效果：

1. 先打开demo，点击“start”等一会儿（本地音频加载需要时间），赛车声音会循环播放。
2. home键回到桌面，找到酷狗音乐APP并打开，播放一首歌曲，这时logcat里面会打印AUDIOFOCUS_LOSS，Demo App会暂停播放。
3. 手动暂停酷狗音乐播放器（log不会有变化，也就是并没有触发AUDIOFOCUS_GAIN）。
4. 设置闹钟，闹钟触发，log显示AUDIOFOCUS_LOSS_TRANSIENT
5. 关闭闹钟，log显示AUDIOFOCUS_GAIN

Demo源码

布局文件就一个按钮，自己写布局哈，完整Demo代码如下，注释写的很清楚了，就不解释了。

public class MainActivity extends AppCompatActivity {
    
    private final String TAG = "xxx";

    private AudioManager mAudioManager;
    private MediaPlayer mMediaPlayer;
    private Button btmMusic;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
    
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initData();
        initView();
    }

    private void initData() {
    
        //初始化AudioManager对象
        mAudioManager = (AudioManager) getSystemService(Context.AUDIO_SERVICE);
        //申请焦点
        mAudioManager.requestAudioFocus(mAudioFocusChange, AudioManager.STREAM_MUSIC, AudioManager.AUDIOFOCUS_GAIN_TRANSIENT);
        AssetFileDescriptor fileDescriptor;
        try {
    
            //获取音频文件
            fileDescriptor = this.getAssets().openFd("11582.mp3");
            //实例化MediaPlayer对象
            mMediaPlayer = new MediaPlayer();
            //设置播放流类型
            mMediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);
            //设置播放源，有多个参数可以选择，具体参考相关文档，本文旨在介绍音频焦点
            mMediaPlayer.setDataSource(fileDescriptor.getFileDescriptor(),
                    fileDescriptor.getStartOffset(),
                    fileDescriptor.getLength());
            //设置循环播放
            mMediaPlayer.setLooping(true);
            //准备监听
            mMediaPlayer.setOnPreparedListener(new MediaPlayer.OnPreparedListener() {
    
                @Override
                public void onPrepared(MediaPlayer mp) {
    
                    //准备完成后自动播放
                    mMediaPlayer.start();
                }
            });
            //异步准备
            mMediaPlayer.prepareAsync();
        } catch (IOException e) {
    
            e.printStackTrace();
        }
    }

    private void initView() {
    
        btmMusic = (Button) findViewById(R.id.btm_music);
        if (btmMusic != null) {
    
            btmMusic.setOnClickListener(new View.OnClickListener() {
    
                @Override
                public void onClick(View v) {
    
                    if (mMediaPlayer != null) {
    
                        if (mMediaPlayer.isPlaying()) {
    
                            stop();
                        } else {
    
                            start();
                        }
                    }
                }
            });
        }
    }


    private void start() {
    
        btmMusic.setText("Stop");
        mAudioManager.requestAudioFocus(mAudioFocusChange, AudioManager.STREAM_MUSIC, AudioManager.AUDIOFOCUS_GAIN);
        mMediaPlayer.start();
    }

    private void stop() {
    
        btmMusic.setText("Start");
        mMediaPlayer.pause();

    }

    /** * 焦点变化监听器 */
    private AudioManager.OnAudioFocusChangeListener mAudioFocusChange = new AudioManager.OnAudioFocusChangeListener() {
    
        @Override
        public void onAudioFocusChange(int focusChange) {
    
            switch (focusChange) {
    
                case AudioManager.AUDIOFOCUS_LOSS:
                    //长时间丢失焦点
                    Log.d(TAG, "AUDIOFOCUS_LOSS");
                    stop();
                    //释放焦点
                    mAudioManager.abandonAudioFocus(mAudioFocusChange);
                    break;
                case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT:
                    //短暂性丢失焦点
                    stop();
                    Log.d(TAG, "AUDIOFOCUS_LOSS_TRANSIENT");
                    break;
                case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK:
                    //短暂性丢失焦点并作降音处理
                    Log.d(TAG, "AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK");
                    break;
                case AudioManager.AUDIOFOCUS_GAIN:
                    //重新获得焦点
                    Log.d(TAG, "AUDIOFOCUS_GAIN");
                    start();
                    break;
            }
        }
    };

    @Override
    protected void onDestroy() {
    
        super.onDestroy();
        mMediaPlayer.release();
        mAudioManager.abandonAudioFocus(mAudioFocusChange);
    }
}

音频焦点的实用场景有哪些？

• 打开酷狗音乐播放一首歌曲，再打开B站，播放视频，这时酷狗会自动暂停，按返回键退出视频播放时，酷狗又会自动恢复播放音乐。

官网怎么描述音频焦点的？

音频焦点改进
AudioManager.requestAudioFocus()