android 音频处理mediaplay介绍

ublic void onAudioFocusChange(int focusChange) {

switch (focusChange) {

case AudioManager.AUDIOFOCUS_GAIN:

// resume playback

if (mMediaPlayer == null) initMediaPlayer();

else if (!mMediaPlayer.isPlaying()) mMediaPlayer.start();

mMediaPlayer.setVolume(1.0f, 1.0f);

break;

case AudioManager.AUDIOFOCUS_LOSS:

// Lost focus for an unbounded amount of time: stop playback and release media player

if (mMediaPlayer.isPlaying()) mMediaPlayer.stop();

mMediaPlayer.release();

mMediaPlayer = null;

break;

case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT:

// Lost focus for a short time, but we have to stop

// playback. We don't release the media player because playback

// is likely to resume

if (mMediaPlayer.isPlaying()) mMediaPlayer.pause();

break;

case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK:

// Lost focus for a short time, but it's ok to keep playing

// at an attenuated level

if (mMediaPlayer.isPlaying()) mMediaPlayer.setVolume(0.1f, 0.1f);

break;

}

}

记住音频焦点API仅在APIlevel 8 (Android2.2)及更高版本上可以，所以如果你想支持更早的Android版本，你必须在可能时采取兼容性的策略使用特性，如果不可能,you should adopt a backward compatibility strategy that allows you touse this feature if available, and fall back seamlessly if not.

你可以用反射的方式调用音频焦点方法或自己在一个单独的类(叫做AudioFocusHelper)中实现所有的音频焦点功能来达到向前兼容.下面是一个这样的类：

[java]

public class AudioFocusHelper implements AudioManager.OnAudioFocusChangeListener {

AudioManager mAudioManager;

// 这里是其它的字段，你可能要保存一个接口的引用，这个接口

// 被用于与你的service通讯以报告焦点的变化.

public AudioFocusHelper(Context ctx, ) {

mAudioManager = (AudioManager) mContext.getSystemService(Context.AUDIO_SERVICE);

// ...

}

public boolean requestFocus() {

return AudioManager.AUDIOFOCUS_REQUEST_GRANTED ==

mAudioManager.requestAudioFocus(mContext, AudioManager.STREAM_MUSIC,

AudioManager.AUDIOFOCUS_GAIN);

}

public boolean abandonFocus() {

return AudioManager.AUDIOFOCUS_REQUEST_GRANTED ==

mAudioManager.abandonAudioFocus(this);

}

@Override

public void onAudioFocusChange(int focusChange) {

// 让你的service知道焦点变化了

}

}

你可以仅在检测到系统运行的是API level 8 或更早的版本时才创建AudioFocusHelper类的实例.例如：

if (android.os.Build.VERSION.SDK_INT >= 8) {

mAudioFocusHelper = new AudioFocusHelper(getApplicationContext(), this);

} else {

mAudioFocusHelper = null;

}

public class AudioFocusHelper implements AudioManager.OnAudioFocusChangeListener {

AudioManager mAudioManager;

// 这里是其它的字段，你可能要保存一个接口的引用，这个接口

// 被用于与你的service通讯以报告焦点的变化.

public AudioFocusHelper(Context ctx, ) {

mAudioManager = (AudioManager) mContext.getSystemService(Context.AUDIO_SERVICE);

// ...

}

public boolean requestFocus() {

return AudioManager.AUDIOFOCUS_REQUEST_GRANTED ==

mAudioManager.requestAudioFocus(mContext, AudioManager.STREAM_MUSIC,

AudioManager.AUDIOFOCUS_GAIN);

}

public boolean abandonFocus() {

return AudioManager.AUDIOFOCUS_REQUEST_GRANTED ==

mAudioManager.abandonAudioFocus(this);

}

@Override

public void onAudioFocusChange(int focusChange) {

// 让你的service知道焦点变化了

}

}

你可以仅在检测到系统运行的是API level 8 或更早的版本时才创建AudioFocusHelper类的实例.例如：

if (android.os.Build.VERSION.SDK_INT >= 8) {

mAudioFocusHelper = new AudioFocusHelper(getApplicationContext(), this);

} else {

mAudioFocusHelper = null;

}

清理

前面提到过，一个MediaPlayer对象可以消耗掉大量的系统资源，所以你应该仅在需要它时保持它并在用完时立即释放.明确的调用清理方法而不是依靠系统的垃圾收集机制是很重要的，因为在被收集之前MediaPlayer可能会存在很长时间，虽然此时它只是占用内存而不影响其它的媒体相关的资源.所以，当你使用一个service时，你应该总四重写