前言
当我们点击屏幕按键时，就会听到touch音，那么touch音是如何播放起来的呢，由于最近项目需求顺便熟悉下了touch音的逻辑。
正文
谈touch逻辑首先要说下这个类ViewRootImpl.java，位于frameworks/base/core/java/android/view下，ViewRootImpl的主要功能：
A：链接WindowManager和DecorView的纽带，更广一点可以说是Window和View之间的纽带。
B：完成View的绘制过程，包括measure、layout、draw过程。
C：向DecorView分发收到的用户发起的event事件，如按键，触屏等事件。
关于ViewRootImpl的源码可参照博客ViewRootImpl类源码解析，我们从performFocusNavigation()入手
private boolean performFocusNavigation(KeyEvent event) {
//略
if (v.requestFocus(direction, mTempRect)) {
playSoundEffect(SoundEffectConstants.getContantForFocusDirection(direction));
return true;
}
//略
return false;
}当我们点击某个控件时，会先触发performFocusNavigation()这个方法，然后当控件获取到focus后便会调用playSoundEffect()方法，我只截取了performFocusNavigation()中关键代码playSoundEffect()部分，来看下playSoundEffect()这个方法
public void playSoundEffect(int effectId) {
checkThread();
try {
final AudioManager audioManager = getAudioManager();
switch (effectId) {
case SoundEffectConstants.CLICK:
audioManager.playSoundEffect(AudioManager.FX_KEY_CLICK);
return;
case SoundEffectConstants.NAVIGATION_DOWN:
audioManager.playSoundEffect(AudioManager.FX_FOCUS_NAVIGATION_DOWN);
return;
case SoundEffectConstants.NAVIGATION_LEFT:
audioManager.playSoundEffect(AudioManager.FX_FOCUS_NAVIGATION_LEFT);
return;
case SoundEffectConstants.NAVIGATION_RIGHT:
audioManager.playSoundEffect(AudioManager.FX_FOCUS_NAVIGATION_RIGHT);
return;
case SoundEffectConstants.NAVIGATION_UP:
audioManager.playSoundEffect(AudioManager.FX_FOCUS_NAVIGATION_UP);
return;
default:
throw new IllegalArgumentException("unknown effect id " + effectId +
" not defined in " + SoundEffectConstants.class.getCanonicalName());
}
} catch (IllegalStateException e) {
// Exception thrown by getAudioManager() when mView is null
Log.e(mTag, "FATAL EXCEPTION when attempting to play sound effect: " + e);
e.printStackTrace();
}
}发现调用了audioManager的playSoundEffect()方法，audiomanager就不说了，接触android audio最先接触的可能就是AudioManager了，音量控制，声音焦点申请等。接着看
public void playSoundEffect(int effectType) {
if (effectType < 0 || effectType >= NUM_SOUND_EFFECTS) {
return;
}
//查询是否开启touch音，如果settings中关闭了，则直接返回
if (!querySoundEffectsEnabled(Process.myUserHandle().getIdentifier())) {
return;
}
final IAudioService service = getService();
try {
//调用到AudioService的playSoundEffect()
service.playSoundEffect(effectType);
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}查询touch音是否可播放，因为毕竟在android的setting中有个touch音的开关，如果可播放则调用到AudioService的playSoundEffect()
public void playSoundEffect(int effectType) {
playSoundEffectVolume(effectType, -1.0f);
}
public void playSoundEffectVolume(int effectType, float volume) {
if (effectType >= AudioManager.NUM_SOUND_EFFECTS || effectType < 0) {
Log.w(TAG, "AudioService effectType value " + effectType + " out of range");
return;
}
sendMsg(mAudioHandler, MSG_PLAY_SOUND_EFFECT, SENDMSG_QUEUE,
effectType, (int) (volume * 1000), null, 0);
}其实AudioService初始化的时候会创建一个子线HandlerThread,HandlerThread主要处理一些相对耗时的操作，这里将播放touch音的功能放在了这个子线程中去执行，这样避免了主线程的阻塞，其实大家在做mediaplayer播放时也建议放在子线程去播放，接下来看看handler里对消息的处理，关键代码如下
case MSG_PLAY_SOUND_EFFECT:
if (msg.obj == null) {
onPlaySoundEffect(msg.arg1, msg.arg2, 0);
} else {
onPlaySoundEffect(msg.arg1, msg.arg2, (int) msg.obj);
}
break;直接调用onPlaySoundEffect()的方法
private void onPlaySoundEffect(int effectType, int volume) {
synchronized (mSoundEffectsLock) {
//初始化mSoundPool和要播放的资源文件
onLoadSoundEffects();
if (mSoundPool == null) {
return;
}
float volFloat;
// use default if volume is not specified by caller
if (volume < 0) {
volFloat = (float)Math.pow(10, (float)sSoundEffectVolumeDb/20);
} else {
volFloat = volume / 1000.0f;
}
if (SOUND_EFFECT_FILES_MAP[effectType][1] > 0) {
//播放touch音
mSoundPool.play(SOUND_EFFECT_FILES_MAP[effectType][1],
volFloat, volFloat, 0, 0, 1.0f);
} else {
MediaPlayer mediaPlayer = new MediaPlayer();
try {
String filePath = Environment.getRootDirectory() + SOUND_EFFECTS_PATH +
SOUND_EFFECT_FILES.get(SOUND_EFFECT_FILES_MAP[effectType][0]);
mediaPlayer.setDataSource(filePath);
mediaPlayer.setAudioStreamType(AudioSystem.STREAM_SYSTEM);
mediaPlayer.prepare();
mediaPlayer.setVolume(volFloat);
mediaPlayer.setOnCompletionListener(new OnCompletionListener() {
public void onCompletion(MediaPlayer mp) {
cleanupPlayer(mp);
}
});
mediaPlayer.setOnErrorListener(new OnErrorListener() {
public boolean onError(MediaPlayer mp, int what, int extra) {
cleanupPlayer(mp);
return true;
}
});
mediaPlayer.start();
} catch (IOException ex) {
Log.w(TAG, "MediaPlayer IOException: "+ex);
} catch (IllegalArgumentException ex) {
Log.w(TAG, "MediaPlayer IllegalArgumentException: "+ex);
} catch (IllegalStateException ex) {
Log.w(TAG, "MediaPlayer IllegalStateException: "+ex);
}
}
}
}最终通过soundPool来播放指定的资源文件实现了touch音的播放，因此大家在工作中如果有什么需要对应touch音的逻辑，可参照AudioService的onPlaySoundEffect()中的逻辑。
比如指定touch音的AudioAttributes使touch音输出到指定的device上等。
总结
touch音的流程就简单分析到这里，欢迎大家交流指正。
努力学习ing~