Android中获取各种服务是哪里来的

Posted 2022-12-09 泼墨成空

      当app第一次加载时就开始注册了那些服务，具体来说就是在应用创建ContextImpl实例的时候调用了SystemServiceRegistry类来进行注册，其注册的服务（就是具体的相关的服务的实例）保存在HashMap的对象SYSTEM_SERVICE_FETCHERS中：

     

	private static final HashMap<String, ServiceFetcher<?>> SYSTEM_SERVICE_FETCHERS = new HashMap<String, ServiceFetcher<?>>();

       以下就是常用的服务注册：

   

		registerService(Context.ACTIVITY_SERVICE, ActivityManager.class,
				new CachedServiceFetcher<ActivityManager>() 
					@Override
					public ActivityManager createService(ContextImpl ctx) 
						return new ActivityManager(ctx.getOuterContext(),
								ctx.mMainThread.getHandler());
					
				);

		registerService(Context.ALARM_SERVICE, AlarmManager.class,
				new CachedServiceFetcher<AlarmManager>() 
					@Override
					public AlarmManager createService(ContextImpl ctx) 
						IBinder b = ServiceManager
								.getService(Context.ALARM_SERVICE);
						IAlarmManager service = IAlarmManager.Stub
								.asInterface(b);
						return new AlarmManager(service, ctx);
					
				);

		registerService(Context.AUDIO_SERVICE, AudioManager.class,
				new CachedServiceFetcher<AudioManager>() 
					@Override
					public AudioManager createService(ContextImpl ctx) 
						return new AudioManager(ctx);
					
				);

		registerService(Context.MEDIA_ROUTER_SERVICE, MediaRouter.class,
				new CachedServiceFetcher<MediaRouter>() 
					@Override
					public MediaRouter createService(ContextImpl ctx) 
						return new MediaRouter(ctx);
					
				);

		registerService(Context.BLUETOOTH_SERVICE, BluetoothManager.class,
				new CachedServiceFetcher<BluetoothManager>() 
					@Override
					public BluetoothManager createService(ContextImpl ctx) 
						return new BluetoothManager(ctx);
					
				);
 。。。。。。。。。。。。。。。。。。。。。。。
 

        注册时调用了registerService（）方法：

    

	private static <T> void registerService(String serviceName,
			Class<T> serviceClass, ServiceFetcher<T> serviceFetcher) 
		//保存服务名称
		SYSTEM_SERVICE_NAMES.put(serviceClass, serviceName);
		//保存服务实例
		SYSTEM_SERVICE_FETCHERS.put(serviceName, serviceFetcher);