闪光灯降功耗方案

在android中打开闪光灯的方法有两种，一种是获取硬件服务，通过反射的方式来操作闪光灯。另外一种是获得Camera对象，通过设置Camera的参数来操作闪光灯。一下是一个操作闪光灯的工具类：实现了两种方式操作闪光灯。通过switchFlashlight方法是通过反射的方式操作，通过turnLightOn，turnLightOff方法操作是通过设置Camera来操作闪关灯的。    为了达到将功耗的目的，需要把闪光灯打开的方式从操作Camera改为直接获得硬件结点进行操作的方式。成立由驱动工程师和应用工程师组成的小组，设计出通过在应用中添加额外放射代码，以及在系统服务CameraService中添加直接操作硬件结点/dev/flashlight的方式 控制FlashLight开关的方案，最终顺利完成功耗电流测试。    private static final Object iHardwareService;      private static final Method setFlashEnabledMethod;      static {          iHardwareService = getHardwareService();   //静态代码块  获得Method方法  获得ICameraService的接口        setFlashEnabledMethod = getSetFlashEnabledMethod(iHardwareService);          if (iHardwareService == null) {              Log.v(TAG, "This device does supports control of a flashlight");          } else {              Log.v(TAG, "This device does not support control of a flashlight");          }      }   /**      * 通过反射来操作闪光灯      */     private static Object getHardwareService() { // 反射获得Class对象        Class<?> serviceManagerClass = maybeForName("android.os.ServiceManager");          if (serviceManagerClass == null) {              return null;          } //从Class对象获得Method对象        Method getServiceMethod = maybeGetMethod(serviceManagerClass,  "getService", String.class);          if (getServiceMethod == null) {              return null;          }  // 从Method 对象获得cameraservice服务的Object对象        Object hardwareService = invoke(getServiceMethod, null, "cameraservice");          if (hardwareService == null) {              return null;          }  // 获得ICameraService的Stub的Class         Class<?> iHardwareServiceStubClass = maybeForName("android.os.ICameraService$Stub");          if (iHardwareServiceStubClass == null) {              return null;          } //获得 ICameraService的asInterface 最终回返回一个客户端的操作类        Method asInterfaceMethod = maybeGetMethod(iHardwareServiceStubClass,  "asInterface", IBinder.class);          if (asInterfaceMethod == null) {              return null;          }          return invoke(asInterfaceMethod, null, hardwareService);      }    public static void switchFlashlight(boolean active) {          setFlashlight(active);      }      static void disableFlashlight() {          setFlashlight(false);      }      private static void setFlashlight(boolean active) {          if (iHardwareService != null) {              invoke(setFlashEnabledMethod, iHardwareService, active);          }      }  }    private static Object invoke(Method method, Object instance, Object... args) {          try {              return method.invoke(instance, args);          } catch (Exception e) {              Log.w(TAG, "Unexpected error while invoking " + method, e);              return null;          }      }   private static Method getSetFlashEnabledMethod(Object iHardwareService) {          if (iHardwareService == null) {              return null;          }          Class<?> proxyClass = iHardwareService.getClass();          return maybeGetMethod(proxyClass, "setFlashlightEnabled", boolean.class);      }      private static Class<?> maybeForName(String name) {          try {              return Class.forName(name);          } catch (ClassNotFoundException cnfe) {              // OK              return null;          } catch (Exception re) {              re.printStackTrace();              Log.w(TAG, "Unexpected error while finding class " + name, re);              return null;          }      }