AudioService调整stream音量

//设置stream音量

mRingVolumePlayer.setStreamVolume(index);

在这里，streamVolume就是我们要设置的音量大小，接着就是调用AudioManager的方法进行设置。

3.AudioManager.java

publicvoidsetStreamVolume(intstreamType,intindex,intflags){

//IAudioService是AudioService的本地代理

IAudioServiceservice=getService();

try{

service.setStreamVolume(streamType,index,flags);

}catch(RemoteExceptione){

Log.e(TAG,"DeadobjectinsetStreamVolume",e);

}

}

这就开始调用AudioService的相关方法设置音量：streamType假设为STREAM_RING，

flags为FLAG_REMOVE_SOUND_AND_VIBRATE

4.AudioService.java

publicvoidsetStreamVolume(intstreamType,intindex,intflags){

//获取stream的状态，在AudioService的构造函数中createStreamStates()时创建

VolumeStreamStatestreamState=mStreamStates[STREAM_VOLUME_ALIAS[streamType]];

//原来stream的音量

finalintoldIndex=(streamState.muteCount()!=0)?streamState.mLastAudibleIndex: streamState.mIndex;

……

//获取stream的音量和最大音量一半的平均值

index=rescaleIndex(index*10,streamType,STREAM_VOLUME_ALIAS[streamType]);

setStreamVolumeInt(STREAM_VOLUME_ALIAS[streamType],index,false,true);

}

privatevoidsetStreamVolumeInt(intstreamType,intindex,booleanforce,boolean lastAudible)

{

VolumeStreamStatestreamState=mStreamStates[streamType];

//假设没有被静音

if(streamState.setIndex(index,lastAudible)||force){

//发送baseid为MSG_SET_SYSTEM_VOLUME的msg

sendMsg(mAudioHandler,MSG_SET_SYSTEM_VOLUME,streamType,SENDMSG_NOOP,0,0,

streamState,0);

}

}

//SetIndex实际上就是判断当前的Index和要设置的index是否一致，不同才进行变更

publicbooleansetIndex(intindex,booleanlastAudible){

intoldIndex=mIndex;

mIndex=getValidIndex(index);

if(oldIndex!=mIndex){

if(lastAudible){

mLastAudibleIndex=mIndex;

}

//Applychangetoallstreamsusingthisoneasalias

intnumStreamTypes=AudioSystem.getNumStreamTypes();

for(intstreamType=numStreamTypes-1;streamType>=0;streamType--){

if(streamType!=mStreamType

&&STREAM_VOLUME_ALIAS[streamType]==mStreamType){

mStreamStates[streamType].setIndex(rescaleIndex(mIndex,mStreamType, streamType),lastAudible);

}

}

returntrue;

}else{

returnfalse;

}

}

在处理刚才发送那个Message时：

AudioHandler{

publicvoidhandleMessage(Messagemsg){

//一般对于内置的stream都是返回0

intbaseMsgWhat=getMsgBase(msg.what);

switch(baseMsgWhat){

caseMSG_SET_SYSTEM_VOLUME:

setSystemVolume((VolumeStreamState)msg.obj);

break;

}

}

privatevoidsetSystemVolume(VolumeStreamStatestreamState){

//这一步调用AudioSystem的方法，再通过JNI对底层直接操作

setStreamVolumeIndex(streamState.mStreamType,streamState.mIndex);

//Applychangetoallstreamsusingthisoneasalias

intnumStreamTypes=AudioSystem.getNumStreamTypes();

for(intstreamType=numStreamTypes-1;streamType>=0;streamType--){

if(streamType!=streamState.mStreamType&&

STREAM_VOLUME_ALIAS[streamType]==streamState.mStreamType){

setStreamVolumeIndex(streamType,mStreamStates[streamType].mIndex);

}

}

//Postapersistvolumemsg

sendMsg(mAudioHandler,MSG_PERSIST_VOLUME,streamState.mStreamType,

SENDMSG_REPLACE,1,1,streamState,PERSIST_DELAY);

}

重点看：setStreamVolumeIndex()

AudioSystem下

publicstaticnativeintsetStreamVolumeIndex(intstream,intindex);

它的实现在：

5./frameworks/base/media/libmedia/android_media_AudioSystem.cpp

staticint

android_media_AudioSystem_setStreamVolumeIndex(JNIEnv*env,jobjectthiz,jintstream, jintindex)

{

returncheck_AudioSystem_Command(AudioSystem::setStreamVolumeIndex(static_cast <audio_stream_type_t>(stream),index));

}

6.AudioSystem.cpp

//设置stream的音量

status_tAudioSystem::setStreamVolumeIndex(audio_stream_type_tstream,intindex)

{

status_tAudioSystem::setStreamVolumeIndex(audio_stream_type_tstream,intindex)

{

//获取AudioSystem中的AudioPolicyService的本地代理

constsp<IAudioPolicyService>&aps=AudioSystem::get_audio_policy_service();

if(aps==0)returnPERMISSION_DENIED;

returnaps->setStreamVolumeIndex(stream,index);

}

}

constsp<IAudioPolicyService>&AudioSystem::get_audio_policy_service()

{

gLock.lock();

if(gAudioPolicyService.get()==0){

//获取ServiceManager

sp<IServiceManager>sm=defaultServiceManager();

sp<IBinder>binder;

do{

//获取audiopolicyservice

binder=sm->getService(String16("media.audio_policy"));

if(binder!=0)

break;

//0.5s

usleep(500000);

}while(true);

if(gAudioPolicyServiceClient==NULL){

gAudioPolicyServiceClient=newAudioPolicyServiceClient();

}

binder->linkToDeath(gAudioPolicyServiceClient);

//这一步是获取获取AudioPolicyService的BpBinder形式，然后将它赋给gAudioPolicyService

//的mRemote

gAudioPolicyService=interface_cast<IAudioPolicyService>(binder);

gLock.unlock();

}else{

gLock.unlock();

}

returngAudioPolicyService;

}

AudioPolicyService.cpp

status_tAudioPolicyService::setStreamVolumeIndex(audio_stream_type_tstream,intindex)

{

//这是一个指针：structaudio_policy*mpAudioPolicy(AudioPolicyService.h)

if(mpAudioPolicy==NULL){

returnNO_INIT;

}

if(!checkPermission()){

returnPERMISSION_DENIED;

}

if(stream<0||stream>=AUDIO_STREAM_CNT){

returnBAD_VALUE;

}

returnmpAudioPolicy->set_stream_volume_index(mpAudioPolicy,stream,index);

}

在这里正式转入对驱动的操作。