content: /*
   * Copyright (C) 2012 ZXing authors
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package com.jinlin.zxing;
  
  import android.content.Context;
  import android.content.SharedPreferences;
  import android.hardware.Sensor;
  import android.hardware.SensorEvent;
  import android.hardware.SensorEventListener;
  import android.hardware.SensorManager;
  import android.preference.PreferenceManager;
  import com.google.zxing.camera.CameraManager;
  import com.google.zxing.camera.FrontLightMode;
  
  /**
   * Detects ambient light and switches on the front light when very dark, and off
   * again when sufficiently light.
   * 
   * @author Sean Owen
   * @author Nikolaus Huber
   */
  final class AmbientLightManager implements SensorEventListener {
  
  	private static final float TOO_DARK_LUX = 45.0f;
  	private static final float BRIGHT_ENOUGH_LUX = 450.0f;
  
  	private final Context context;
  	private CameraManager cameraManager;
  
  	/**
  	 * 光传感器
  	 */
  	private Sensor lightSensor;
  
  	AmbientLightManager(Context context) {
  		this.context = context;
  	}
  
  	void start(CameraManager cameraManager) {
  		this.cameraManager = cameraManager;
  		SharedPreferences sharedPrefs = PreferenceManager
  				.getDefaultSharedPreferences(context);
  		if (FrontLightMode.readPref(sharedPrefs) == FrontLightMode.AUTO) {
  			SensorManager sensorManager = (SensorManager) context
  					.getSystemService(Context.SENSOR_SERVICE);
  			lightSensor = sensorManager.getDefaultSensor(Sensor.TYPE_LIGHT);
  			if (lightSensor != null) {
  				sensorManager.registerListener(this, lightSensor,
  						SensorManager.SENSOR_DELAY_NORMAL);
  			}
  		}
  	}
  
  	void stop() {
  		if (lightSensor != null) {
  			SensorManager sensorManager = (SensorManager) context
  					.getSystemService(Context.SENSOR_SERVICE);
  			sensorManager.unregisterListener(this);
  			cameraManager = null;
  			lightSensor = null;
  		}
  	}
  
  	/**
  	 * 该方法会在周围环境改变后回调，然后根据设置好的临界值决定是否打开闪光灯
  	 */
  	@Override
  	public void onSensorChanged(SensorEvent sensorEvent) {
  		float ambientLightLux = sensorEvent.values[0];
  		if (cameraManager != null) {
  			if (ambientLightLux <= TOO_DARK_LUX) {
  				cameraManager.setTorch(true);
  			}
  			else if (ambientLightLux >= BRIGHT_ENOUGH_LUX) {
  				cameraManager.setTorch(false);
  			}
  		}
  	}
  
  	@Override
  	public void onAccuracyChanged(Sensor sensor, int accuracy) {
  		// do nothing
  	}
  
  }
  