Android 通话：后台通话过程中锁屏解锁，发现听筒内存在锁屏提示音

【概 率】：必现

solution：

修改文件：./frameworks/av/services/audiopolicy/AudioPolicyManager.cpp

status_t AudioPolicyManager::checkAndSetVolume(audio_stream_type_t stream,
                                                   int index,
                                                   audio_io_handle_t output,
                                                   audio_devices_t device,
                                                   int delayMs,
                                                   bool force)
{
    ALOGD(" checkAndSetVolume stream = %d index = %d output = %d device = 0x%x delayMs = %d force = %d"
        ,stream,index,output,device,delayMs,force);
    // do not change actual stream volume if the stream is muted
    if (mOutputs.valueFor(output)->mMuteCount[stream] != 0) {
        ALOGVV("checkAndSetVolume() stream %d muted count %d",
              stream, mOutputs.valueFor(output)->mMuteCount[stream]);
        return NO_ERROR;
    }
    //add start
    if(stream == AUDIO_STREAM_SYSTEM && isInCall())
        index=0;
    //add end

    // do not change in call volume if bluetooth is connected and vice versa
    if ((stream == AUDIO_STREAM_VOICE_CALL &&
            mForceUse[AUDIO_POLICY_FORCE_FOR_COMMUNICATION] == AUDIO_POLICY_FORCE_BT_SCO) ||
        (stream == AUDIO_STREAM_BLUETOOTH_SCO &&
                mForceUse[AUDIO_POLICY_FORCE_FOR_COMMUNICATION] != AUDIO_POLICY_FORCE_BT_SCO)) {
        ALOGD("checkAndSetVolume() cannot set stream %d volume with force use = %d for comm",
             stream, mForceUse[AUDIO_POLICY_FORCE_FOR_COMMUNICATION]);
        return INVALID_OPERATION;
    }
    //..................
}

if(stream == AUDIO_STREAM_SYSTEM && isInCall())
        index=0;