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

public void setStreamVolume(int streamType, int index, int flags) {

//IAudioService 是AudioService的本地代理

        IAudioService service = getService();

        try {

            service.setStreamVolume(streamType, index, flags);

        } catch (RemoteException e) {

            Log.e(TAG, "Dead object in setStreamVolume", 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

public void setStreamVolume(int streamType, int index, int flags) {

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

VolumeStreamState streamState = mStreamStates[STREAM_VOLUME_ALIAS[streamType]];

//原来stream的音量

final int oldIndex = (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);

}

private void setStreamVolumeInt(int streamType, int index, boolean force, boolean                      lastAudible)

{

VolumeStreamState streamState = mStreamStates[streamType];

//假设没有被静音

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

//发送base id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

public boolean setIndex(int index, boolean lastAudible) {

     int oldIndex = mIndex;

     mIndex = getValidIndex(index);

     if (oldIndex != mIndex) {

          if (lastAudible) {

               mLastAudibleIndex = mIndex;

          }

      // Apply change to all streams using this one as alias

      int numStreamTypes = AudioSystem.getNumStreamTypes();

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

        if (streamType != mStreamType

&& STREAM_VOLUME_ALIAS[streamType] == mStreamType) {

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

         }

      }

       return true;

} else {

        return false;

   }

}

在处理刚才发送那个Message时：

AudioHandler {

public void handleMessage(Message msg) {

//一般对于内置的stream都是返回0

int baseMsgWhat = getMsgBase(msg.what);

switch (baseMsgWhat) {

 case MSG_SET_SYSTEM_VOLUME:

       setSystemVolume((VolumeStreamState) msg.obj);

       break;

}

}

private void setSystemVolume(VolumeStreamState streamState) {

 //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);

// 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 &&

            STREAM_VOLUME_ALIAS[streamType] == streamState.mStreamType) {

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

       }

}

// Post a persist volume msg

sendMsg(mAudioHandler, MSG_PERSIST_VOLUME, streamState.mStreamType,

         SENDMSG_REPLACE, 1, 1, streamState, PERSIST_DELAY);

}

重点看：setStreamVolumeIndex()

AudioSystem下

public static native int setStreamVolumeIndex(int stream, int index);

它的实现在：

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

static int

android_media_AudioSystem_setStreamVolumeIndex(JNIEnv *env, jobject thiz, jint stream,  jint index)

{

    return check_AudioSystem_Command(AudioSystem::setStreamVolumeIndex(static_cast  (stream), index));

}

6.AudioSystem.cpp

//设置stream的音量

status_t AudioSystem::setStreamVolumeIndex(audio_stream_type_t stream, int index)

{

status_t AudioSystem::setStreamVolumeIndex(audio_stream_type_t stream, int index)

{

//获取AudioSystem中的AudioPolicyService的本地代理

const sp& aps = AudioSystem::get_audio_policy_service();

if (aps == 0) return PERMISSION_DENIED;

return aps->setStreamVolumeIndex(stream, index);

}

}

const sp& AudioSystem::get_audio_policy_service()

{

  gLock.lock();

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

//获取ServiceManager

        sp sm = defaultServiceManager();

        sp binder;

        do {

//获取audiopolicyservice

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

            if (binder != 0)

                break;

// 0.5 s

            usleep(500000);

        } while(true);

        if (gAudioPolicyServiceClient == NULL) {

            gAudioPolicyServiceClient = new AudioPolicyServiceClient();

        }

        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(binder);

        gLock.unlock();

    } else {

        gLock.unlock();

    }

    return gAudioPolicyService;

}

AudioPolicyService.cpp

status_t AudioPolicyService::setStreamVolumeIndex(audio_stream_type_t stream, int index)

{

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

    if (mpAudioPolicy == NULL) {

        return NO_INIT;

    }

    if (!checkPermission()) {

        return PERMISSION_DENIED;

    }

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

        return BAD_VALUE;

    }

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

}

在这里正式转入对驱动的操作。

 

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