一、按键音调用流程摘要：按键音播放的总体逻辑是先找到系统中按键音的资源，然后调用SoundPool.load让系统加载音频资源，加载成功后在onLoadComplete回调中会返回一个非0的soundID ，用于播放时指定特定的音频，最后在需要播放按键音的时候直接根据soundID播放
1.Android按键音接口Android按键音只有两个常用接口，分别是：
原生设置APP中SoundFragment.java调用的设置按键音开关的接口：mAudioManager.loadSoundEffects()和mAudioManager.unloadSoundEffects()
private void setSoundEffectsEnabled(boolean enabled) {
mAudioManager = (AudioManager) getActivity().getSystemService(Context.AUDIO_SERVICE); //1
if (enabled) {
mAudioManager.loadSoundEffects();
} else {
mAudioManager.unloadSoundEffects();
}
Settings.System.putInt(getActivity().getContentResolver(),
Settings.System.SOUND_EFFECTS_ENABLED, enabled ? 1 : 0);
}
先调用AudioManager的loadSoundEffects方法，然后会调用到AudioService的loadSoundEffects方法
View.java中播放按键音的接口：playSoundEffect
public boolean performClick() {
// We still need to call this method to handle the cases where performClick() was called
// externally, instead of through performClickInternal()
notifyAutofillManagerOnClick();
final boolean result;
final ListenerInfo li = mListenerInfo;
if (li != null && li.mOnClickListener != null) {
playSoundEffect(SoundEffectConstants.CLICK);//调用会经过ViewRootImpl.java，最终调用到AudioService中
li.mOnClickListener.onClick(this);
result = true;
} else {
result = false;
}
sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
notifyEnterOrExitForAutoFillIfNeeded(true);
return result;
}最终会调用到AudioService的playSoundEffect方法
2.onLoadSoundEffects()方法上述的两个方法调用到AudioService之后，分别通过sendMsg向handler发送MSG_LOAD_SOUND_EFFECTS和MSG_PLAY_SOUND_EFFECT信息，handler在收到信息后会进行相应的操作，但是不管是哪个操作，都会调用到onLoadSoundEffects()方法
loadSoundEffects的调用流程（非重点）：
public boolean loadSoundEffects() {
int attempts = 3;
LoadSoundEffectReply reply = new LoadSoundEffectReply();
synchronized (reply) {
//调用sendMsg方法
sendMsg(mAudioHandler, MSG_LOAD_SOUND_EFFECTS, SENDMSG_QUEUE, 0, 0, reply, 0);
while ((reply.mStatus == 1) && (attempts-- > 0)) {
try {
reply.wait(SOUND_EFFECTS_LOAD_TIMEOUT_MS);
} catch (InterruptedException e) {
Log.w(TAG, "loadSoundEffects Interrupted while waiting sound pool loaded.");
}
}
}
return (reply.mStatus == 0);
}
//sendMsg方法是对handler.sendMessageAtTime的封装
private static void sendMsg(Handler handler, int msg,
int existingMsgPolicy, int arg1, int arg2, Object obj, int delay) {
if (existingMsgPolicy == SENDMSG_REPLACE) {
handler.removeMessages(msg);
} else if (existingMsgPolicy == SENDMSG_NOOP && handler.hasMessages(msg)) {
return;
}
synchronized (mLastDeviceConnectMsgTime) {
long time = SystemClock.uptimeMillis() + delay;
if (msg == MSG_SET_A2DP_SRC_CONNECTION_STATE ||
msg == MSG_SET_A2DP_SINK_CONNECTION_STATE ||
msg == MSG_SET_HEARING_AID_CONNECTION_STATE ||
msg == MSG_SET_WIRED_DEVICE_CONNECTION_STATE ||
msg == MSG_A2DP_DEVICE_CONFIG_CHANGE ||
msg == MSG_BTA2DP_DOCK_TIMEOUT) {
if (mLastDeviceConnectMsgTime >= time) {
// add a little delay to make sure messages are ordered as expected
time = mLastDeviceConnectMsgTime + 30;
}
mLastDeviceConnectMsgTime = time;
}
handler.sendMessageAtTime(handler.obtainMessage(msg, arg1, arg2, obj), time);
}
}
//在handleMessage中处理消息
@Override
public void handleMessage(Message msg) {
......
case MSG_PLAY_SOUND_EFFECT:
//调用onPlaySoundEffect
onPlaySoundEffect(msg.arg1, msg.arg2);
break;
}
private void onPlaySoundEffect(int effectType, int volume) {
synchronized (mSoundEffectsLock) {
//最终会调用到onLoadSoundEffects
onLoadSoundEffects();
......
}playSoundEffect的调用流程（非重点）：
public void playSoundEffect(int effectType) {
playSoundEffectVolume(effectType, -1.0f);
}
public void playSoundEffectVolume(int effectType, float volume) {
// do not try to play the sound effect if the system stream is muted
if (isStreamMutedByRingerOrZenMode(STREAM_SYSTEM)) {
return;
}
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);
}
//在handleMessage中处理消息
@Override
public void handleMessage(Message msg) {
......
case MSG_PLAY_SOUND_EFFECT:
onPlaySoundEffect(msg.arg1, msg.arg2);
break;
}
private void onPlaySoundEffect(int effectType, int volume) {
synchronized (mSoundEffectsLock) {
onLoadSoundEffects();
......
}如上所述最终都会调用onLoadSoundEffects方法
在onLoadSoundEffects方法中主要完成以下几件事：
调用loadTouchSoundAssets方法解析XML文件，获得音源文件名，初始化数组，将音源文件与数组中元素一一对应 补全音源文件路径，调用SoundPool.load方法 将SoundPool.load方法返回的sampleId保存在数组中，作为之后play方法的参数
先来看loadTouchSoundAssets方法，代码如下：
private void loadTouchSoundAssets() {
XmlResourceParser parser = null;
// only load assets once.
//SOUND_EFFECT_FILES是一个存放字符串的List，里面存放的是音频资源的名称
if (!SOUND_EFFECT_FILES.isEmpty()) {
return;
}
//此方法执行：
//1.SOUND_EFFECT_FILES.add("Effect_Tick.ogg"); 向SOUND_EFFECT_FILES添加一个音频资源的名称
//2.初始化一个二维数组SOUND_EFFECT_FILES_MAP。行数为10，列数为2，第一列都为0，第二列都为-1
loadTouchSoundAssetDefaults();
try {
//获得XML对象
parser = mContext.getResources().getXml(com.android.internal.R.xml.audio_assets);
XmlUtils.beginDocument(parser, TAG_AUDIO_ASSETS);
//getAttributeValue方法用于获取传入的Attribute名称对应的Value，这里是"1.0"
String version = parser.getAttributeValue(null, ATTR_VERSION);
boolean inTouchSoundsGroup = false;
if (ASSET_FILE_VERSION.equals(version)) {
while (true) {
//nextElement方法用于切换到XML的下一层
XmlUtils.nextElement(parser);
//获取当前parser的名称，这里是"group"
String element = parser.getName();
if (element == null) {
break;
}
if (element.equals(TAG_GROUP)) {
String name = parser.getAttributeValue(null, ATTR_GROUP_NAME);
if (GROUP_TOUCH_SOUNDS.equals(name)) {
inTouchSoundsGroup = true;
break;
}
}
}
//遍历XML中剩下的所有元素
while (inTouchSoundsGroup) {
XmlUtils.nextElement(parser);
String element = parser.getName();
if (element == null) {
break;
}
if (element.equals(TAG_ASSET)) {
String id = parser.getAttributeValue(null, ATTR_ASSET_ID);
String file = parser.getAttributeValue(null, ATTR_ASSET_FILE);
int fx;
try {
//getField的对象是.class文件(.java文件的预编译产物，只进行一些变量即宏的替换)，这里即AudioManager.class
//根据传入的id获得AudioManager.class中对应的对象，例如传入的是"FX_KEY_CLICK"，得到的是AudioManager中定义的public static final int FX_KEY_CLICK = 0
Field field = AudioManager.class.getField(id);
fx = field.getInt(null);
} catch (Exception e) {
Log.w(TAG, "Invalid touch sound ID: "+id);
continue;
}
//根据之前XML中读取的file取出其在SOUND_EFFECT_FILES的位置
//此时SOUND_EFFECT_FILES只有一个元素即"Effect_Tick.ogg"
//如果不存在则加入到SOUND_EFFECT_FILES中
int i = SOUND_EFFECT_FILES.indexOf(file);
if (i == -1) {
i = SOUND_EFFECT_FILES.size();
SOUND_EFFECT_FILES.add(file);
}
SOUND_EFFECT_FILES_MAP[fx][0] = i;
} else {
break;
}
}
}
} catch (Resources.NotFoundException e) {
Log.w(TAG, "audio assets file not found", e);
} catch (XmlPullParserException e) {
Log.w(TAG, "XML parser exception reading touch sound assets", e);
} catch (IOException e) {
Log.w(TAG, "I/O exception reading touch sound assets", e);
} finally {
if (parser != null) {
parser.close();
}
}
}
private void loadTouchSoundAssetDefaults() {
SOUND_EFFECT_FILES.add("Effect_Tick.ogg");
for (int i = 0; i < AudioManager.NUM_SOUND_EFFECTS; i++) {
SOUND_EFFECT_FILES_MAP[i][0] = 0;
SOUND_EFFECT_FILES_MAP[i][1] = -1;
}
}
经过loadTouchSoundAssets初始化后，SOUND_EFFECT_FILES数组为：
{ "Effect_Tick.ogg" , "KeypressStandard.ogg" , "KeypressSpacebar.ogg" ,
"KeypressDelete.ogg" , "KeypressReturn.ogg" , "KeypressInvalid.ogg" }SOUND_EFFECT_FILES_MAP数组为：
{{0, -1}, {0, -1}, {0, -1}, {0, -1}, {0, -1}, {1, -1}, {2, -1}, {3, -1}, {4, -1}, {5, -1}}再来看真正的onLoadSoundEffects方法：
private boolean onLoadSoundEffects() {
int status;
synchronized (mSoundEffectsLock) {
if (!mSystemReady) {
Log.w(TAG, "onLoadSoundEffects() called before boot complete");
return false;
}
if (mSoundPool != null) {
return true;
}
loadTouchSoundAssets();//根据XML文件初始化数组，如上所述
//初始化SoundPool
mSoundPool = new SoundPool.Builder()
.setMaxStreams(NUM_SOUNDPOOL_CHANNELS)
.setAudioAttributes(new AudioAttributes.Builder()
.setUsage(AudioAttributes.USAGE_ASSISTANCE_SONIFICATION)
.setContentType(AudioAttributes.CONTENT_TYPE_SONIFICATION)
.build())
.build();
mSoundPoolCallBack = null;
mSoundPoolListenerThread = new SoundPoolListenerThread();
//这个线程以及下面的代码主要是去设置SoundPoolCallback，不求甚解
mSoundPoolListenerThread.start();
int attempts = 3;
while ((mSoundPoolCallBack == null) && (attempts-- > 0)) {
try {
// Wait for mSoundPoolCallBack to be set by the other thread
mSoundEffectsLock.wait(SOUND_EFFECTS_LOAD_TIMEOUT_MS);
} catch (InterruptedException e) {
Log.w(TAG, "Interrupted while waiting sound pool listener thread.");
}
}
if (mSoundPoolCallBack == null) {
Log.w(TAG, "onLoadSoundEffects() SoundPool listener or thread creation error");
if (mSoundPoolLooper != null) {
mSoundPoolLooper.quit();
mSoundPoolLooper = null;
}
mSoundPoolListenerThread = null;
mSoundPool.release();
mSoundPool = null;
return false;
}
/*
* poolId table: The value -1 in this table indicates that corresponding
* file (same index in SOUND_EFFECT_FILES[] has not been loaded.
* Once loaded, the value in poolId is the sample ID and the same
* sample can be reused for another effect using the same file.
*/
//创建一个和SOUND_EFFECT_FILES一样大的数组并将元素初始化为-1
int[] poolId = new int[SOUND_EFFECT_FILES.size()];
for (int fileIdx = 0; fileIdx < SOUND_EFFECT_FILES.size(); fileIdx++) {
poolId[fileIdx] = -1;
}
/*
* Effects whose value in SOUND_EFFECT_FILES_MAP[effect][1] is -1 must be loaded.
* If load succeeds, value in SOUND_EFFECT_FILES_MAP[effect][1] is > 0:
* this indicates we have a valid sample loaded for this effect.
*/
int numSamples = 0;
for (int effect = 0; effect < AudioManager.NUM_SOUND_EFFECTS; effect++) {
// Do not load sample if this effect uses the MediaPlayer
if (SOUND_EFFECT_FILES_MAP[effect][1] == 0) {
continue;
}
//第一次走到这里时这个判断一定为真，因为poolId中所有元素都为-1
if (poolId[SOUND_EFFECT_FILES_MAP[effect][0]] == -1) {
//getSoundEffectFilePath会根据SOUND_EFFECT_FILES中的内容补全出音频文件的具体路径
String filePath = getSoundEffectFilePath(effect);
//调用SoundPool.load方法，返回的sampleId被保存在SOUND_EFFECT_FILES_MAP和poolId中
int sampleId = mSoundPool.load(filePath, 0);
if (sampleId <= 0) {
Log.w(TAG, "Soundpool could not load file: "+filePath);
} else {
SOUND_EFFECT_FILES_MAP[effect][1] = sampleId;
poolId[SOUND_EFFECT_FILES_MAP[effect][0]] = sampleId;
numSamples++;
}
} else {
SOUND_EFFECT_FILES_MAP[effect][1] =
poolId[SOUND_EFFECT_FILES_MAP[effect][0]];
}
}
// wait for all samples to be loaded
if (numSamples > 0) {
mSoundPoolCallBack.setSamples(poolId);
attempts = 3;
status = 1;
while ((status == 1) && (attempts-- > 0)) {
try {
mSoundEffectsLock.wait(SOUND_EFFECTS_LOAD_TIMEOUT_MS);
status = mSoundPoolCallBack.status();
} catch (InterruptedException e) {
Log.w(TAG, "Interrupted while waiting sound pool callback.");
}
}
} else {
status = -1;
}
if (mSoundPoolLooper != null) {
mSoundPoolLooper.quit();
mSoundPoolLooper = null;
}
mSoundPoolListenerThread = null;
if (status != 0) {
Log.w(TAG,
"onLoadSoundEffects(), Error "+status+ " while loading samples");
for (int effect = 0; effect < AudioManager.NUM_SOUND_EFFECTS; effect++) {
if (SOUND_EFFECT_FILES_MAP[effect][1] > 0) {
SOUND_EFFECT_FILES_MAP[effect][1] = -1;
}
}
mSoundPool.release();
mSoundPool = null;
}
}
return (status == 0);
}
private String getSoundEffectFilePath(int effectType) {
String filePath = Environment.getProductDirectory() + SOUND_EFFECTS_PATH
+ SOUND_EFFECT_FILES.get(SOUND_EFFECT_FILES_MAP[effectType][0]);
if (!new File(filePath).isFile()) {
filePath = Environment.getRootDirectory() + SOUND_EFFECTS_PATH
+ SOUND_EFFECT_FILES.get(SOUND_EFFECT_FILES_MAP[effectType][0]);
}
Log.d(TAG, "SoundEffectFilePath is : "+filePath);
return filePath;
}
代码中难懂的部分基本上都有注释，核心其实就是为SoundPool的load方法准备参数，其中有些数组嵌套的部分比较绕，但是只要把数组都写出来就一目了然了
onLoadSoundEffects基本上就是loadSoundEffects的全部内容，最后再来看一下onPlaySoundEffect的剩余部分
private void onPlaySoundEffect(int effectType, int volume) {
synchronized (mSoundEffectsLock) {
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) {
//调用SoundPool的play方法
mSoundPool.play(SOUND_EFFECT_FILES_MAP[effectType][1],
volFloat, volFloat, 0, 0, 1.0f);
Log.w(TAG, "Touch tone played");
} else {
MediaPlayer mediaPlayer = new MediaPlayer();
try {
String filePath = getSoundEffectFilePath(effectType);
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);
}
}
}
}
其中值得注意的点其实就只有SoundPool的play方法，其中传入了音量大小和之前load返回的sampleId
二、替换原生按键音摘要：替换原生按键音的主要思路是：在初始化的时候在相关数组中增加自己自定义的音频资源，为了达到这个目的需要在文件中增加一些代表自己文件资源的常量，具体在哪个文件中增加，其实完全可以在熟悉源码流程之后模仿源码来增加；之后在播放按键音的时候主动调用自己的按键音资源就可以了；最后当然别忘了把音频文件push到设备中去。
需要修改的文件如下：
/frameworks/base/media/java/android/media/AudioManager.java
需要增加自己的音频种类，起名为：FX_KEYPRESS_CUSTOM，并把最大音频数量修改为11
/**
* Invalid keypress sound
* @see #playSoundEffect(int)
*/
public static final int FX_KEYPRESS_INVALID = 9;
/**
* @hide Custom sound
* @see #playSoundEffect(int)
*/
public static final int FX_KEYPRESS_CUSTOM = 10;
/**
* @hide Number of sound effects
*/
public static final int NUM_SOUND_EFFECTS = 11;需要注意的是自己增加的常量最好全部hide标记，这样可以免去执行make update-api指令，同时并不会影响使用，之后的修改都会遵循这一原则
/frameworks/base/core/java/android/view/SoundEffectConstants.java
同样需要增加一个常量：
public static final int CLICK = 0;
public static final int NAVIGATION_LEFT = 1;
public static final int NAVIGATION_UP = 2;
public static final int NAVIGATION_RIGHT = 3;
public static final int NAVIGATION_DOWN = 4;
/**
* @hide Custom click sound
*/
public static final int CLICK_CUSTOM = 5;/frameworks/base/core/res/res/xml/audio_assets.xml
在XML文件中增加一个自己的音频文件，注意id和之前在AudioManager.java中增加的常量一致，file和push到设备中的文件名保持一致
准备工作已经完成了，现在来修改一下调用流程，主动调用自己的按键音
/frameworks/base/core/java/android/view/View.java
调用playSoundEffect时传入之前增加的常量：
public boolean performClick() {
// We still need to call this method to handle the cases where performClick() was called
// externally, instead of through performClickInternal()
notifyAutofillManagerOnClick();
final boolean result;
final ListenerInfo li = mListenerInfo;
if (li != null && li.mOnClickListener != null) {
playSoundEffect(SoundEffectConstants.CLICK_CUSTOM);//修改这里
li.mOnClickListener.onClick(this);
result = true;
} else {
result = false;
}
sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
notifyEnterOrExitForAutoFillIfNeeded(true);
return result;
}/frameworks/base/core/java/android/view/ViewRootImpl.java
View.java之后会调用到ViewRootImpl.java中，在switch/case中加入我们自己的情况：
@Override
public void playSoundEffect(int effectId) {
checkThread();
Log.d(mTag, "playSoundEffect");
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;
//增加的case语句
case SoundEffectConstants.CLICK_CUSTOM:
audioManager.playSoundEffect(AudioManager.FX_KEYPRESS_CUSTOM);
Log.d(mTag, "play my SoundEffect");
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();
}
}以上就是修改的全部文件了，实际上只有5个文件，比预想的要简单的多，这全都要归功于Android源码出色的设计模式使其在代码上高度解耦
别忘了把音频文件push到设备里面，否则会启动异常的哦！push的路径为：/system/media/audio/ui/
可能有些小伙伴对于为什么要修改上面的文件有一些疑问，这里附上播放按键音的UML时序图，只要熟悉调用流程，就明白了
三、调节按键音音量方法其实在之前的讲解过程中已经说到了，在调用SoundPool.play的时候其实会传入左右声道的音量值，只要按图索骥找到之前是在哪里传入的音量就可以啦！其实是在playSoundEffectVolume方法传入的音量值，那么只要在这个方法的参数中传入你想要的值就行了。