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.google.zxing.camera;
  
  import android.hardware.Camera;
  import android.util.Log;
  
  /**
   * 该类用于检测手机上摄像头的个数，如果有两个摄像头，则取背面的摄像头
   */
  public final class OpenCameraInterface {
  
  	private static final String TAG = OpenCameraInterface.class.getName();
  
  	private OpenCameraInterface() {
  	}
  
  	/**
  	 * Opens a rear-facing camera with {@link Camera#open(int)}, if one exists,
  	 * or opens camera 0.
  	 */
  	public static Camera open() {
  
  		int numCameras = Camera.getNumberOfCameras();
  		if (numCameras == 0) {
  			Log.w(TAG, "No cameras!");
  			return null;
  		}
  
  		int index = 0;
  		while (index < numCameras) {
  			Camera.CameraInfo cameraInfo = new Camera.CameraInfo();
  			Camera.getCameraInfo(index, cameraInfo);
  			// CAMERA_FACING_BACK：手机背面的摄像头
  			if (cameraInfo.facing == Camera.CameraInfo.CAMERA_FACING_BACK) {
  				break;
  			}
  			index++;
  		}
  
  		Camera camera;
  		if (index < numCameras) {
  			Log.i(TAG, "Opening camera #" + index);
  			camera = Camera.open(index);
  		} else {
  			Log.i(TAG, "No camera facing back; returning camera #0");
  			camera = Camera.open(0);
  		}
  
  		return camera;
  	}
  
  }
  