CarAudioService介绍

packages/services/Car/service/src/com/android/car/audio/CarAudioService.java

CarAudioService是CarService服务中的其中一种关于Audio的特定服务。主要是负责与汽车音响系统进行交互。对音频进行分区，分区内的焦点分配，音量调节，音频路由等功能。因为CarAudioService是CarService中的其中一个服务，所以，我们直接make CarService 就可以进行编译。

CarAudioManager API方法

其实看下来CarAudioManager提供的方法主要集中在音量和音频分区两个方面。我们后面再详细讲解。其中大部分都行SystemApi方法，只有系统应用能调用，或者用java反射的方式调用。

服务的获取

应用成功连接CarService之后，调用Car的getCarManager(String servicename)方法获取服务

mCarAudioManager = (CarAudioManager) getCar().getCarManager(Car.AUDIO_SERVICE);

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• 1.CarService启动后，会在onCreate方法中构造一个ICarImpl类。

  //CarService.java
  public void onCreate() {
          mICarImpl = new ICarImpl(this,
                  mVehicle,
                  SystemInterface.Builder.defaultSystemInterface(this).build(),
                  mVehicleInterfaceName);
          mICarImpl.init();
      }
  

• 2.ICarImpl类在构造方法中创建CarAudioService服务，并添加到服务列表内

  //ICarImpl.java
  ICarImpl(Context serviceContext, IVehicle vehicle, SystemInterface systemInterface,
              String vehicleInterfaceName,
              @Nullable CarUserService carUserService,
              @Nullable CarWatchdogService carWatchdogService,
              @Nullable ICarPowerPolicySystemNotification powerPolicyDaemon) {
          LimitedTimingsTraceLog t = new LimitedTimingsTraceLog(
                  CAR_SERVICE_INIT_TIMING_TAG, Trace.TRACE_TAG_SYSTEM_SERVER,
                  CAR_SERVICE_INIT_TIMING_MIN_DURATION_MS);
          t.traceBegin("ICarImpl.constructor");
          //创建CarAudioService
          mCarAudioService = constructWithTrace(t, CarAudioService.class,
                  () -> new CarAudioService(serviceContext));
           ...
          //添加到服务列表
          allServices.add(mCarAudioService);
      }
  

• 3.应用通过Car的getCarManager(String servicename)方法获取CarAudioManager。

  //Car.java
  public Object getCarManager(String serviceName) {
          CarManagerBase manager;
  
                      IBinder binder = mService.getCarService(serviceName);
                      manager = createCarManagerLocked(serviceName, binder);
  
          return manager;
      }
  

• 4.Car.java与ICarImpl.java通过aidl通讯，所有会走到ICarImpl的getCarService方法中，通过servicename获取到CarAudoService，返回给Car.java中。

  //ICarImpl.java
  @Override
      public IBinder getCarService(String serviceName) {
          if (!mFeatureController.isFeatureEnabled(serviceName)) {
              Log.w(CarLog.TAG_SERVICE, "getCarService for disabled service:" + serviceName);
              return null;
          }
          switch (serviceName) {
              case Car.AUDIO_SERVICE:
                  return mCarAudioService;
          }
      }
  

• 5.将servicename和CarAudioService传递到createCarManagerLocked方法，创建一个CarAudioManager，同时将CarAudioService传入CarAudioManager中。

  //Car.java
   private CarManagerBase createCarManagerLocked(String serviceName, IBinder binder) {
          CarManagerBase manager = null;
          switch (serviceName) {
              case AUDIO_SERVICE:
                  manager = new CarAudioManager(this, binder);
                  break;
          }
          return manager;
      }
  

构造方法

 public CarAudioService(Context context) {
        mContext = context;
        //1.获取TelephonyManager和AudioManager服务，用于判断通话状态，调用系统Audio方法实现大部分audio功能。
        mTelephonyManager = (TelephonyManager) mContext.getSystemService(Context.TELEPHONY_SERVICE);
        mAudioManager = (AudioManager) mContext.getSystemService(Context.AUDIO_SERVICE);
        //2.从config.xml的文件中获取mUseDynamicRouting属性。 mUseDynamicRouting是尤为重要的属性，为true时。才能开启汽车的动态路由配置。
        mUseDynamicRouting = mContext.getResources().getBoolean(R.bool.audioUseDynamicRouting);
        mKeyEventTimeoutMs =
                mContext.getResources().getInteger(R.integer.audioVolumeKeyEventTimeoutMs);
        mUseHalDuckingSignals = mContext.getResources().getBoolean(
                R.bool.audioUseHalDuckingSignals);
        //3.创建CarAudioSetting用于加载和保存音量设置。创建 mUidToZoneMap用于管理音频分区和uid关联集合。
        mUidToZoneMap = new HashMap<>();
        mCarVolumeCallbackHandler = new CarVolumeCallbackHandler();
        mCarAudioSettings = new CarAudioSettings(mContext.getContentResolver());

        mAudioZoneIdToUserIdMapping = new SparseIntArray();
        mAudioVolumeAdjustmentContextsVersion =
                mContext.getResources().getInteger(R.integer.audioVolumeAdjustmentContextsVersion);
        mCarVolume = new CarVolume(mClock,
                mAudioVolumeAdjustmentContextsVersion, mKeyEventTimeoutMs);
        boolean useCarVolumeGroupMuting = mUseDynamicRouting && mContext.getResources().getBoolean(
                R.bool.audioUseCarVolumeGroupMuting);
        if (mAudioVolumeAdjustmentContextsVersion != VERSION_TWO && useCarVolumeGroupMuting) {
            throw new IllegalArgumentException("audioUseCarVolumeGroupMuting is enabled but "
                    + "this requires audioVolumeAdjustmentContextsVersion 2,"
                    + " instead version " + mAudioVolumeAdjustmentContextsVersion + " was found");
        }
        mUseCarVolumeGroupMuting = useCarVolumeGroupMuting;
        mPersistMasterMuteState = !mUseCarVolumeGroupMuting && mContext.getResources().getBoolean(
                R.bool.audioPersistMasterMuteState);
    }

初始化

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CarAudioService初始化方法的调用是在CarAudioService启动，创建ICarImpl对像，调用ICarImpl的init方法，在ICarImpl的init方法初始所有car的 相关服务。

CarAudioService初始化的时候，根据mUseDynamicRouting这个属性走上的完全不一样的逻辑。

  public void init() {
        synchronized (mImplLock) {
            mOccupantZoneService = CarLocalServices.getService(CarOccupantZoneService.class);
            Car car = new Car(mContext, /* service= */null, /* handler= */ null);
            mOccupantZoneManager = new CarOccupantZoneManager(car, mOccupantZoneService);
            if (mUseDynamicRouting) {
                setupDynamicRoutingLocked();//2.设置动态路由
                setupHalAudioFocusListenerLocked();//3.注册来自hal层的焦点监听
                setupAudioConfigurationCallbackLocked();//4.注册Audio播放和配置修改的监听
                setupPowerPolicyListener();//5.启动Power电量监听和Policy策略修改监听
            } else {
                Slog.i(CarLog.TAG_AUDIO, "Audio dynamic routing not enabled, run in legacy mode");
                setupLegacyVolumeChangedListener();//6.设置音量监听
            }
            mAudioManager.setSupportedSystemUsages(SYSTEM_USAGES);//
        }
        restoreMasterMuteState();//
    }

其中setupDynamicRoutingLocked方法是初始化过程中的核心方法。看下具体的代码流程

 private void setupDynamicRoutingLocked() {
      //1.创建AudioPolicy策略
        final AudioPolicy.Builder builder = new AudioPolicy.Builder(mContext);
        builder.setLooper(Looper.getMainLooper());
      //2.加载音频分区
        loadCarAudioZonesLocked();
        for (int i = 0; i < mCarAudioZones.size(); i++) {
            CarAudioZone zone = mCarAudioZones.valueAt(i);
            // Ensure HAL gets our initial value
           //3.给音频分区设置音量增益及对应的index
            zone.synchronizeCurrentGainIndex();
            Slog.v(CarLog.TAG_AUDIO, "Processed audio zone: " + zone);
        }
       //4.给每个CarAudioZones中的CarVolumeGroup配置混音策略，并添加到AudioPolicy策略中。
        CarAudioDynamicRouting.setupAudioDynamicRouting(builder, mCarAudioZones);
       //5.将音量变化的监听回调注册到AudioPolicy中
        CarAudioPolicyVolumeCallback
                .addVolumeCallbackToPolicy(builder, this, mAudioManager,
                        mUseCarVolumeGroupMuting);
        ...
       //6.创建车载音频焦点的管理对象，并且设置到AudioPolicy策略中
        mFocusHandler = CarZonesAudioFocus.createCarZonesAudioFocus(mAudioManager,
                mContext.getPackageManager(),
                mCarAudioZones,
                mCarAudioSettings,
                ENABLE_DELAYED_AUDIO_FOCUS,
                mCarDucking);
        builder.setAudioPolicyFocusListener(mFocusHandler);
        builder.setIsAudioFocusPolicy(true);
        mAudioPolicy = builder.build();
        mFocusHandler.setOwningPolicy(this, mAudioPolicy);
      //7.将AudioPoliy策略注册到AudioManager中
        int r = mAudioManager.registerAudioPolicy(mAudioPolicy);
       ...
        setupOccupantZoneInfo();
    }

总的来说，就是创建AudioPolicy策略，配置音频分区，混音，音频焦点相关策略，并注册到AudioManager中，AuiodManager再传入navie层的AudioPolicy中实现。