Android车载开发初窥

2023-05-24 23:44| 来源: 网络整理| 查看: 265

这个就是AndroidAutoMovie的架构图，总体来说关于android的部分在Framework中添加了大量的车机服务，并且在sdk中提供了api供我们调用，而在底层则添加了嵌入式操作系统相关的架构。关于底层我们只是做一些简单的了解，我们先来看看应用层和Framework层，先来看看这个车机服务是咋起来的！众所周知，android的服务实在systemserver进程中，如果不了解的小伙伴，可以看看我之前写的文章，Android系统启动时，都干了什么？那车机服务是咋起的呢？答案还是在Systemserver里，

private void startOtherServices() { ... if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_AUTOMOTIVE)) { traceBeginAndSlog("StartCarServiceHelperService"); mSystemServiceManager.startService(CAR_SERVICE_HELPER_SERVICE_CLASS); traceEnd(); } ... }

Systemserver通过SystemServiceManager来管理的，所以CAR_SERVICE_HELPER_SERVICE_CLASS同样也被它管理，我们来跟下代码

public SystemService startService(String className) { final Class serviceClass; try { serviceClass = (Class)Class.forName(className); } catch (ClassNotFoundException ex) { Slog.i(TAG, "Starting " + className); throw new RuntimeException("Failed to create service " + className + ": service class not found, usually indicates that the caller should " + "have called PackageManager.hasSystemFeature() to check whether the " + "feature is available on this device before trying to start the " + "services that implement it", ex); } return startService(serviceClass); } /** * Creates and starts a system service. The class must be a subclass of * {@link com.android.server.SystemService}. * * @param serviceClass A Java class that implements the SystemService interface. * @return The service instance, never null. * @throws RuntimeException if the service fails to start. */ @SuppressWarnings("unchecked") public T startService(Class serviceClass) { try { final String name = serviceClass.getName(); Slog.i(TAG, "Starting " + name); Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "StartService " + name); // Create the service. if (!SystemService.class.isAssignableFrom(serviceClass)) { throw new RuntimeException("Failed to create " + name + ": service must extend " + SystemService.class.getName()); } final T service; try { Constructor constructor = serviceClass.getConstructor(Context.class); service = constructor.newInstance(mContext);//反射获取对象 } catch (InstantiationException ex) { throw new RuntimeException("Failed to create service " + name + ": service could not be instantiated", ex); } catch (IllegalAccessException ex) { throw new RuntimeException("Failed to create service " + name + ": service must have a public constructor with a Context argument", ex); } catch (NoSuchMethodException ex) { throw new RuntimeException("Failed to create service " + name + ": service must have a public constructor with a Context argument", ex); } catch (InvocationTargetException ex) { throw new RuntimeException("Failed to create service " + name + ": service constructor threw an exception", ex); } startService(service); return service; } finally { Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER); } } public void startService(@NonNull final SystemService service) { // Register it. mServices.add(service); // Start it. long time = SystemClock.elapsedRealtime(); try { service.onStart();//最终调到了这个方法 } catch (RuntimeException ex) { throw new RuntimeException("Failed to start service " + service.getClass().getName() + ": onStart threw an exception", ex); } warnIfTooLong(SystemClock.elapsedRealtime() - time, service, "onStart"); }

我们通过上面的代码可以看到，它最终是调了 CarServiceHelperService.onStart()这个方法，我们继续跟代码

@Override public void onStart() { Intent intent = new Intent(); intent.setPackage("com.android.car"); intent.setAction(CAR_SERVICE_INTERFACE); if (!getContext().bindServiceAsUser(intent, mCarServiceConnection, Context.BIND_AUTO_CREATE, UserHandle.SYSTEM)) { Slog.wtf(TAG, "cannot start car service"); } System.loadLibrary("car-framework-service-jni"); }

这个方法里，启动一个包名为com.android.car并绑定得到一个binder远端代理，这样就完成了carService的启动，我们不难发现它就是个单独的app,写到这，我突然不免意思到，这个跟前公司智能android机顶盒的流程，简直如出一辙啊，cable线的直播电视app开发中，由中间件适配硬件，提供hal层给Framework调用，我们也是整了一个服务类的apk，这个通过抽象接口调用底层，并且提供binder给应用层绑定，那应用层咋绑定呢，也是通过一个jar包来做和服务类apk通讯，app只需要调用jar包中的api就够了，好了好像跑偏了，言归正传，我们继续说这个单独app,这个源码在哪里呢?/packages/services/Car/service,我们跟进去看一下它的代码

public class CarService extends Service { private static final long WAIT_FOR_VEHICLE_HAL_TIMEOUT_MS = 10_000; private static final boolean IS_USER_BUILD = "user".equals(Build.TYPE); private static final String IVHAL_20 = android.hardware.automotive.vehicle.V2_0.IVehicle.kInterfaceName; private static final String IVHAL_21 = android.hardware.automotive.vehicle.V2_1.IVehicle.kInterfaceName; private CanBusErrorNotifier mCanBusErrorNotifier; private ICarImpl mICarImpl; //提供服务的远端stub private IVehicle mVehicle; //就理解为跟硬件打交道的抽象接口吧 private final VehicleDeathRecipient mVehicleDeathRecipient = new VehicleDeathRecipient(); @Override public void onCreate() { Log.i(CarLog.TAG_SERVICE, "Service onCreate"); mCanBusErrorNotifier = new CanBusErrorNotifier(this /* context */); mVehicle = getVehicle(null /* Any Vehicle HAL interface name */); if (mVehicle == null) { throw new IllegalStateException("Vehicle HAL service is not available."); } try { mVehicleInterfaceName = mVehicle.interfaceDescriptor(); } catch (RemoteException e) { throw new IllegalStateException("Unable to get Vehicle HAL interface descriptor", e); } Log.i(CarLog.TAG_SERVICE, "Connected to " + mVehicleInterfaceName); mICarImpl = new ICarImpl(this, mVehicle, SystemInterface.getDefault(this), mCanBusErrorNotifier); mICarImpl.init(); SystemProperties.set("boot.car_service_created", "1"); linkToDeath(mVehicle, mVehicleDeathRecipient); super.onCreate(); } @Override public int onStartCommand(Intent intent, int flags, int startId) { // keep it alive. return START_STICKY; } @Override public IBinder onBind(Intent intent) { return mICarImpl; } }

通过代码，我们不难发现mICarImpl应该是实现了stub的远端服务，我们跟下它的代码

public class ICarImpl extends ICar.Stub { private final CarServiceBase[] mAllServices; /** Test only service. Populate it only when necessary. */ @GuardedBy("this") private CarTestService mCarTestService; public ICarImpl(Context serviceContext, IVehicle vehicle, SystemInterface systemInterface, CanBusErrorNotifier errorNotifier) { mContext = serviceContext; mHal = new VehicleHal(vehicle); mSystemActivityMonitoringService = new SystemActivityMonitoringService(serviceContext); mCarPowerManagementService = new CarPowerManagementService( mHal.getPowerHal(), systemInterface); mCarSensorService = new CarSensorService(serviceContext, mHal.getSensorHal()); mCarPackageManagerService = new CarPackageManagerService(serviceContext, mCarSensorService, mSystemActivityMonitoringService); mCarInputService = new CarInputService(serviceContext, mHal.getInputHal()); mCarProjectionService = new CarProjectionService(serviceContext, mCarInputService); mGarageModeService = new GarageModeService(mContext, mCarPowerManagementService); mCarInfoService = new CarInfoService(serviceContext, mHal.getInfoHal()); mAppFocusService = new AppFocusService(serviceContext, mSystemActivityMonitoringService); mCarAudioService = new CarAudioService(serviceContext, mHal.getAudioHal(), mCarInputService, errorNotifier); mCarCabinService = new CarCabinService(serviceContext, mHal.getCabinHal()); mCarHvacService = new CarHvacService(serviceContext, mHal.getHvacHal()); mCarRadioService = new CarRadioService(serviceContext, mHal.getRadioHal()); mCarNightService = new CarNightService(serviceContext, mCarSensorService); mInstrumentClusterService = new InstrumentClusterService(serviceContext, mAppFocusService, mCarInputService); mSystemStateControllerService = new SystemStateControllerService(serviceContext, mCarPowerManagementService, mCarAudioService, this); mCarVendorExtensionService = new CarVendorExtensionService(serviceContext, mHal.getVendorExtensionHal()); mPerUserCarServiceHelper = new PerUserCarServiceHelper(serviceContext); mCarBluetoothService = new CarBluetoothService(serviceContext, mCarCabinService, mCarSensorService, mPerUserCarServiceHelper); if (FeatureConfiguration.ENABLE_VEHICLE_MAP_SERVICE) { mVmsSubscriberService = new VmsSubscriberService(serviceContext, mHal.getVmsHal()); mVmsPublisherService = new VmsPublisherService(serviceContext, mHal.getVmsHal()); } if (FeatureConfiguration.ENABLE_DIAGNOSTIC) { mCarDiagnosticService = new CarDiagnosticService(serviceContext, mHal.getDiagnosticHal()); } // Be careful with order. Service depending on other service should be inited later. List allServices = new ArrayList(Arrays.asList( mSystemActivityMonitoringService, mCarPowerManagementService, mCarSensorService, mCarPackageManagerService, mCarInputService, mGarageModeService, mCarInfoService, mAppFocusService, mCarAudioService, mCarCabinService, mCarHvacService, mCarRadioService, mCarNightService, mInstrumentClusterService, mCarProjectionService, mSystemStateControllerService, mCarVendorExtensionService, mCarBluetoothService, mPerUserCarServiceHelper )); if (FeatureConfiguration.ENABLE_VEHICLE_MAP_SERVICE) { allServices.add(mVmsSubscriberService); allServices.add(mVmsPublisherService); } if (FeatureConfiguration.ENABLE_DIAGNOSTIC) { allServices.add(mCarDiagnosticService); } mAllServices = allServices.toArray(new CarServiceBase[0]); } public void init() { mHal.init(); for (CarServiceBase service : mAllServices) { service.init(); } } public void release() { // release done in opposite order from init for (int i = mAllServices.length - 1; i >= 0; i--) { mAllServices[i].release(); } mHal.release(); } public void vehicleHalReconnected(IVehicle vehicle) { mHal.vehicleHalReconnected(vehicle); for (CarServiceBase service : mAllServices) { service.vehicleHalReconnected(); } } //提供对外服务获取api @Override public IBinder getCarService(String serviceName) { switch (serviceName) { case Car.AUDIO_SERVICE: return mCarAudioService; case Car.SENSOR_SERVICE: return mCarSensorService; case Car.INFO_SERVICE: return mCarInfoService; case Car.APP_FOCUS_SERVICE: return mAppFocusService; case Car.PACKAGE_SERVICE: return mCarPackageManagerService; case Car.CABIN_SERVICE: assertCabinPermission(mContext); return mCarCabinService; case Car.DIAGNOSTIC_SERVICE: FeatureUtil.assertFeature(FeatureConfiguration.ENABLE_DIAGNOSTIC); if (FeatureConfiguration.ENABLE_DIAGNOSTIC) { assertAnyDiagnosticPermission(mContext); return mCarDiagnosticService; } case Car.HVAC_SERVICE: assertHvacPermission(mContext); return mCarHvacService; case Car.RADIO_SERVICE: assertRadioPermission(mContext); return mCarRadioService; case Car.CAR_NAVIGATION_SERVICE: assertNavigationManagerPermission(mContext); IInstrumentClusterNavigation navService = mInstrumentClusterService.getNavigationService(); return navService == null ? null : navService.asBinder(); case Car.PROJECTION_SERVICE: assertProjectionPermission(mContext); return mCarProjectionService; case Car.VENDOR_EXTENSION_SERVICE: assertVendorExtensionPermission(mContext); return mCarVendorExtensionService; case Car.VMS_SUBSCRIBER_SERVICE: FeatureUtil.assertFeature(FeatureConfiguration.ENABLE_VEHICLE_MAP_SERVICE); if (FeatureConfiguration.ENABLE_VEHICLE_MAP_SERVICE) { assertVmsSubscriberPermission(mContext); return mVmsSubscriberService; } case Car.TEST_SERVICE: { assertPermission(mContext, Car.PERMISSION_CAR_TEST_SERVICE); synchronized (this) { if (mCarTestService == null) { mCarTestService = new CarTestService(mContext, this); } return mCarTestService; } } default: Log.w(CarLog.TAG_SERVICE, "getCarService for unknown service:" + serviceName); return null; } } }

这么多service看的眼睛都花了，不过确实是在这里面管理添加并缓存的，并且Car还把硬件抽象相关的vehicle传过来了，那各种服务拿到这个硬件接口，不就是可以操作硬件了嘛。以上就是carservice的启动过程。用一张图来表述各个功能模块

image-20230426172520209.png

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