在Android平台上，音量键，主页键(home),都是全局按键，但是主页键是个例外不能被应用所捕获。下面分析一下音量按键的流程，主要从framework层处理开始，至于
EventHub 从驱动的/dev/input/event0获取按键信息到上抛属于Android input 系统方面的流程，下面基于android KK平台分析。
系统层接收音量按键
ViewRootImpl.processKeyEvent 处理Activity 上面收到的按键
private int processKeyEvent(QueuedInputEvent q) {
final KeyEvent event = (KeyEvent)q.mEvent;
if (event.getAction() != KeyEvent.ACTION_UP) {
// If delivering a new key event, make sure the window is
// now allowed to start updating.
handleDispatchDoneAnimating();
}
// Deliver the key to the view hierarchy.
if (mView.dispatchKeyEvent(event)) {
return FINISH_HANDLED;
}
if (shouldDropInputEvent(q)) {
return FINISH_NOT_HANDLED;
}
// If the Control modifier is held, try to interpret the key as a shortcut.
if (event.getAction() == KeyEvent.ACTION_DOWN
&& event.isCtrlPressed()
&& event.getRepeatCount() == 0
&& !KeyEvent.isModifierKey(event.getKeyCode())) {
if (mView.dispatchKeyShortcutEvent(event)) {
return FINISH_HANDLED;
}
if (shouldDropInputEvent(q)) {
return FINISH_NOT_HANDLED;
}
}
// Apply the fallback event policy.
if (mFallbackEventHandler.dispatchKeyEvent(event)) {
return FINISH_HANDLED;
}
if (shouldDropInputEvent(q)) {
return FINISH_NOT_HANDLED;
}
// Handle automatic focus changes.
if (event.getAction() == KeyEvent.ACTION_DOWN) {
int direction = 0;
switch (event.getKeyCode()) {
case KeyEvent.KEYCODE_DPAD_LEFT:
if (event.hasNoModifiers()) {
direction = View.FOCUS_LEFT;
}
break;
case KeyEvent.KEYCODE_DPAD_RIGHT:
if (event.hasNoModifiers()) {
direction = View.FOCUS_RIGHT;
}
break;
case KeyEvent.KEYCODE_DPAD_UP:
if (event.hasNoModifiers()) {
direction = View.FOCUS_UP;
}
break;
case KeyEvent.KEYCODE_DPAD_DOWN:
if (event.hasNoModifiers()) {
direction = View.FOCUS_DOWN;
}
break;
case KeyEvent.KEYCODE_TAB:
if (event.hasNoModifiers()) {
direction = View.FOCUS_FORWARD;
} else if (event.hasModifiers(KeyEvent.META_SHIFT_ON)) {
direction = View.FOCUS_BACKWARD;
}
break;
}
if (direction != 0) {
View focused = mView.findFocus();
if (focused != null) {
View v = focused.focusSearch(direction);
if (v != null && v != focused) {
// do the math the get the interesting rect
// of previous focused into the coord system of
// newly focused view
focused.getFocusedRect(mTempRect);
if (mView instanceof ViewGroup) {
((ViewGroup) mView).offsetDescendantRectToMyCoords(
focused, mTempRect);
((ViewGroup) mView).offsetRectIntoDescendantCoords(
v, mTempRect);
}
if (v.requestFocus(direction, mTempRect)) {
playSoundEffect(SoundEffectConstants
.getContantForFocusDirection(direction));
return FINISH_HANDLED;
}
}
// Give the focused view a last chance to handle the dpad key.
if (mView.dispatchUnhandledMove(focused, direction)) {
return FINISH_HANDLED;
}
} else {
// find the best view to give focus to in this non-touch-mode with no-focus
View v = focusSearch(null, direction);
if (v != null && v.requestFocus(direction)) {
return FINISH_HANDLED;
}
}
}
}
return FORWARD;
} public boolean dispatchKeyEvent(KeyEvent event) {
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onKeyEvent(event, 0);
}
// Give any attached key listener a first crack at the event.
//noinspection SimplifiableIfStatement
ListenerInfo li = mListenerInfo;
if (li != null && li.mOnKeyListener != null && (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnKeyListener.onKey(this, event.getKeyCode(), event)) {
return true;
}
if (event.dispatch(this, mAttachInfo != null
? mAttachInfo.mKeyDispatchState : null, this)) {
return true;
}
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);
}
return false;
} public final boolean dispatch(Callback receiver, DispatcherState state,
Object target) {
switch (mAction) {
case ACTION_DOWN: {
mFlags &= ~FLAG_START_TRACKING;
if (DEBUG) Log.v(TAG, "Key down to " + target + " in " + state
+ ": " + this);
boolean res = receiver.onKeyDown(mKeyCode, this);
if (state != null) {
if (res && mRepeatCount == 0 && (mFlags&FLAG_START_TRACKING) != 0) {
if (DEBUG) Log.v(TAG, " Start tracking!");
state.startTracking(this, target);
} else if (isLongPress() && state.isTracking(this)) {
try {
if (receiver.onKeyLongPress(mKeyCode, this)) {
if (DEBUG) Log.v(TAG, " Clear from long press!");
state.performedLongPress(this);
res = true;
}
} catch (AbstractMethodError e) {
}
}
}
return res;
}
case ACTION_UP:
if (DEBUG) Log.v(TAG, "Key up to " + target + " in " + state
+ ": " + this);
if (state != null) {
state.handleUpEvent(this);
}
return receiver.onKeyUp(mKeyCode, this);
case ACTION_MULTIPLE:
final int count = mRepeatCount;
final int code = mKeyCode;
if (receiver.onKeyMultiple(code, count, this)) {
return true;
}
if (code != KeyEvent.KEYCODE_UNKNOWN) {
mAction = ACTION_DOWN;
mRepeatCount = 0;
boolean handled = receiver.onKeyDown(code, this);
if (handled) {
mAction = ACTION_UP;
receiver.onKeyUp(code, this);
}
mAction = ACTION_MULTIPLE;
mRepeatCount = count;
return handled;
}
return false;
}
return false;
}应用处理完了就会返回，如果没有处理就会流向mFallbackEventHandler.dispatchKeyEvent(event),其实mFallbackEventHandler就是PhoneFallbackEventHandler,接着看
PhoneFallbackEventHandler.dispatchKeyEvent的处理流程
public boolean dispatchKeyEvent(KeyEvent event) {
final int action = event.getAction();
final int keyCode = event.getKeyCode();
if (action == KeyEvent.ACTION_DOWN) {
return onKeyDown(keyCode, event);
} else {
return onKeyUp(keyCode, event);
}
} boolean onKeyDown(int keyCode, KeyEvent event) {
/* ****************************************************************************
* HOW TO DECIDE WHERE YOUR KEY HANDLING GOES.
* See the comment in PhoneWindow.onKeyDown
* ****************************************************************************/
final KeyEvent.DispatcherState dispatcher = mView.getKeyDispatcherState();
switch (keyCode) {
case KeyEvent.KEYCODE_VOLUME_UP:
case KeyEvent.KEYCODE_VOLUME_DOWN:
case KeyEvent.KEYCODE_VOLUME_MUTE: {
getAudioManager().handleKeyDown(event, AudioManager.USE_DEFAULT_STREAM_TYPE);
return true;
}
......
}
return false;
}AudioManager处理音量
从上面分析知道PhoneFallbackEventHandler处理一些Activity没有处理的全局按键，音量键接着进入handleKeyDown处理流程
public void handleKeyDown(KeyEvent event, int stream) {
int keyCode = event.getKeyCode();
switch (keyCode) {
case KeyEvent.KEYCODE_VOLUME_UP:
case KeyEvent.KEYCODE_VOLUME_DOWN:
/*
* Adjust the volume in on key down since it is more
* responsive to the user.
*/
int flags = FLAG_SHOW_UI | FLAG_VIBRATE;
if (mUseMasterVolume) {
adjustMasterVolume(
keyCode == KeyEvent.KEYCODE_VOLUME_UP
? ADJUST_RAISE
: ADJUST_LOWER,
flags);
} else {
adjustSuggestedStreamVolume(
keyCode == KeyEvent.KEYCODE_VOLUME_UP
? ADJUST_RAISE
: ADJUST_LOWER,
stream,
flags);
}
break;
case KeyEvent.KEYCODE_VOLUME_MUTE:
if (event.getRepeatCount() == 0) {
if (mUseMasterVolume) {
setMasterMute(!isMasterMute());
} else {
// TODO: Actually handle MUTE.
}
}
break;
}
}
再接着就进入adjustSuggestedStreamVolume，如果当前的streamType为STREAM_REMOTE_MUSIC，则走mMediaFocusControl.adjustRemoteVolume，其它类型
走音量的通用设置流程adjustStreamVolume
AudioService音量控制流程
从adjustSuggestedStreamVolume 过渡到adjustStreamVolume，进入音量设置的主要流程，主要对流类型，设备，声音设备状态，步进大小进行判断处理，另外蓝牙设
备音量和主设备音量进行了控制，最后通过mVolumePanel刷新界面音量显示，并且广播通过上层应用。
public void adjustStreamVolume(int streamType, int direction, int flags,
String callingPackage) {
if (mUseFixedVolume) {
return;
}
if (DEBUG_VOL) Log.d(TAG, "adjustStreamVolume() stream="+streamType+", dir="+direction);
ensureValidDirection(direction);
ensureValidStreamType(streamType);
// use stream type alias here so that streams with same alias have the same behavior,
// including with regard to silent mode control (e.g the use of STREAM_RING below and in
// checkForRingerModeChange() in place of STREAM_RING or STREAM_NOTIFICATION)
int streamTypeAlias = mStreamVolumeAlias[streamType];
VolumeStreamState streamState = mStreamStates[streamTypeAlias];
final int device = getDeviceForStream(streamTypeAlias);
int aliasIndex = streamState.getIndex(device);
boolean adjustVolume = true;
int step;
// skip a2dp absolute volume control request when the device
// is not an a2dp device
if ((device & AudioSystem.DEVICE_OUT_ALL_A2DP) == 0 &&
(flags & AudioManager.FLAG_BLUETOOTH_ABS_VOLUME) != 0) {
return;
}
if (mAppOps.noteOp(STEAM_VOLUME_OPS[streamTypeAlias], Binder.getCallingUid(),
callingPackage) != AppOpsManager.MODE_ALLOWED) {
return;
}
// reset any pending volume command
synchronized (mSafeMediaVolumeState) {
mPendingVolumeCommand = null;
}
flags &= ~AudioManager.FLAG_FIXED_VOLUME;
if ((streamTypeAlias == AudioSystem.STREAM_MUSIC) &&
((device & mFixedVolumeDevices) != 0)) {
flags |= AudioManager.FLAG_FIXED_VOLUME;
// Always toggle between max safe volume and 0 for fixed volume devices where safe
// volume is enforced, and max and 0 for the others.
// This is simulated by stepping by the full allowed volume range
if (mSafeMediaVolumeState == SAFE_MEDIA_VOLUME_ACTIVE &&
(device & mSafeMediaVolumeDevices) != 0) {
step = mSafeMediaVolumeIndex;
} else {
step = streamState.getMaxIndex();
}
if (aliasIndex != 0) {
aliasIndex = step;
}
} else {
// convert one UI step (+/-1) into a number of internal units on the stream alias
step = rescaleIndex(10, streamType, streamTypeAlias);
}
// If either the client forces allowing ringer modes for this adjustment,
// or the stream type is one that is affected by ringer modes
if (((flags & AudioManager.FLAG_ALLOW_RINGER_MODES) != 0) ||
(streamTypeAlias == getMasterStreamType())) {
int ringerMode = getRingerMode();
// do not vibrate if already in vibrate mode
if (ringerMode == AudioManager.RINGER_MODE_VIBRATE) {
flags &= ~AudioManager.FLAG_VIBRATE;
}
// Check if the ringer mode changes with this volume adjustment. If
// it does, it will handle adjusting the volume, so we won't below
adjustVolume = checkForRingerModeChange(aliasIndex, direction, step);
}
int oldIndex = mStreamStates[streamType].getIndex(device);
if (adjustVolume && (direction != AudioManager.ADJUST_SAME)) {
// Check if volume update should be send to AVRCP
if (streamTypeAlias == AudioSystem.STREAM_MUSIC &&
(device & AudioSystem.DEVICE_OUT_ALL_A2DP) != 0 &&
(flags & AudioManager.FLAG_BLUETOOTH_ABS_VOLUME) == 0) {
synchronized (mA2dpAvrcpLock) {
if (mA2dp != null && mAvrcpAbsVolSupported) {
mA2dp.adjustAvrcpAbsoluteVolume(direction);
}
}
}
if ((direction == AudioManager.ADJUST_RAISE) &&
!checkSafeMediaVolume(streamTypeAlias, aliasIndex + step, device)) {
Log.e(TAG, "adjustStreamVolume() safe volume index = "+oldIndex);
mVolumePanel.postDisplaySafeVolumeWarning(flags);
} else if (streamState.adjustIndex(direction * step, device)) {
// Post message to set system volume (it in turn will post a message
// to persist). Do not change volume if stream is muted.
sendMsg(mAudioHandler,
MSG_SET_DEVICE_VOLUME,
SENDMSG_QUEUE,
device,
0,
streamState,
0);
}
}
int index = mStreamStates[streamType].getIndex(device);
sendVolumeUpdate(streamType, oldIndex, index, flags);
}蓝牙音量的控制
有上可知，如果当前连接了蓝牙也将对音量进行控制，mA2dp.adjustAvrcpAbsoluteVolume，以后分析。
音频处理设置
音频处理由AudioHandler来进行，
adjustStreamVolume做完相关处理后，通过sendMsg发送音量变化消息MSG_SET_DEVICE_VOLUME进入
AudioHandler.handleMessage调用AudioHandler.setDeviceVolume
private void setDeviceVolume(VolumeStreamState streamState, int device) {
// Apply volume
streamState.applyDeviceVolume(device);
// Apply change to all streams using this one as alias
int numStreamTypes = AudioSystem.getNumStreamTypes();
for (int streamType = numStreamTypes - 1; streamType >= 0; streamType--) {
if (streamType != streamState.mStreamType &&
mStreamVolumeAlias[streamType] == streamState.mStreamType) {
// Make sure volume is also maxed out on A2DP device for aliased stream
// that may have a different device selected
int streamDevice = getDeviceForStream(streamType);
if ((device != streamDevice) && mAvrcpAbsVolSupported &&
((device & AudioSystem.DEVICE_OUT_ALL_A2DP) != 0)) {
mStreamStates[streamType].applyDeviceVolume(device);
}
mStreamStates[streamType].applyDeviceVolume(streamDevice);
}
}
// Post a persist volume msg
sendMsg(mAudioHandler,
MSG_PERSIST_VOLUME,
SENDMSG_QUEUE,
device,
0,
streamState,
PERSIST_DELAY);
} public void applyDeviceVolume(int device) {
int index;
if (isMuted()) {
index = 0;
} else if ((device & AudioSystem.DEVICE_OUT_ALL_A2DP) != 0 &&
mAvrcpAbsVolSupported) {
index = (mIndexMax + 5)/10;
} else {
index = (getIndex(device) + 5)/10;
}
AudioSystem.setStreamVolumeIndex(mStreamType, index, device);
}AudioSystem处理
applyDeviceVolume处理完，AudioSystem就开始接着往下设置setStreamVolumeIndex，该接口也即android_media_AudioSystem_setStreamVolumeIndex
在frameworks\base\core\jni\android_media_AudioSystem.cpp中有定义。
static int android_media_AudioSystem_setStreamVolumeIndex(JNIEnv *env,
jobject thiz,
jint stream,
jint index,
jint device)
{
return check_AudioSystem_Command(
AudioSystem::setStreamVolumeIndex(static_cast <audio_stream_type_t>(stream),
index,
(audio_devices_t)device));
}status_t AudioSystem::setStreamVolumeIndex(audio_stream_type_t stream,
int index,
audio_devices_t device)
{
const sp<IAudioPolicyService>& aps = AudioSystem::get_audio_policy_service();
if (aps == 0) return PERMISSION_DENIED;
return aps->setStreamVolumeIndex(stream, index, device);
}status_t AudioPolicyService::setStreamVolumeIndex(audio_stream_type_t stream,
int index,
audio_devices_t device)
{
if (mpAudioPolicy == NULL) {
return NO_INIT;
}
if (!settingsAllowed()) {
return PERMISSION_DENIED;
}
if (uint32_t(stream) >= AUDIO_STREAM_CNT) {
return BAD_VALUE;
}
Mutex::Autolock _l(mLock);
if (mpAudioPolicy->set_stream_volume_index_for_device) {
return mpAudioPolicy->set_stream_volume_index_for_device(mpAudioPolicy,
stream,
index,
device);
} else {
return mpAudioPolicy->set_stream_volume_index(mpAudioPolicy, stream, index);
}
}mpAudioPolicy作为audio_policy类型的对象，其方法主要在Hardware层实现，可以查看相关文件audio_policy_hal.cpp 或者 audio_policy.c，也就是在库
audio.a2dp.xxx.so ,audio.btmic.xxx.so，audio.primary.xxxx 库中实现.
AudioPolicyService.cpp构造函数中就有hw_get_module(AUDIO_POLICY_HARDWARE_MODULE_ID, &module);打印HAL层的库。
通知上层应用
sendVolumeUpdate在音量设置完成之后，完成画面刷新，并广播通知上层应用。
扩展连接：http://www.2cto.com/kf/201409/337102.html
更多音频策略相关流程后续分析。
