相机开发(前后摄像头小笔记)

由于应用支持Android 2.2 版本，所以直接使用Camera.open()打开Camera，但据反应在某些平板上无后置摄像头但有前置摄像头的时候，则无法使用(因为open()方法只能打开后置摄像头)。

故使用反射则中解决，默认使用后置。(在台电平板上已测试通过)

/**
     * 打开默认相机
     * 默认打开后置摄像头，若没有则打开前置
     * @return
     */
    public static Camera openDefaultCamera()
    {

        Camera camera = null;

        try
        {
            Class<?> cameraClass = Camera.class;
            Method method = cameraClass.getMethod("getNumberOfCameras");
            int cameraNum = (Integer) method.invoke(null);

            int backId = -1;
            int frontId = -1;
            int defaultId = 0;

            Class<?>[] classes = cameraClass.getDeclaredClasses();

            Class<?> cameraInfoCalss = null;

            for (Class<?> clz : classes)
            {
                String name = clz.getName();

                if (name.equals("android.hardware.Camera$CameraInfo"))
                {
                    cameraInfoCalss = clz;
                }
            }

            if (cameraInfoCalss == null)
            {
                return camera;
            }

            Field backField = cameraInfoCalss.getField("CAMERA_FACING_BACK");
            Field frontField = cameraInfoCalss.getField("CAMERA_FACING_FRONT");

            //获取前后摄像头默认facing int值
            int backFacing = backField.getInt(cameraInfoCalss);
            int frontFacing = frontField.getInt(cameraInfoCalss);

            java.lang.reflect.Constructor cons = cameraInfoCalss.getConstructor();

            if (cons == null)
            {
                return camera;
            }

            Object cameraInfo = cons.newInstance();

            for (int i = 0; i < cameraNum; i++)
            {
                Method getCameraInfo = cameraClass.getMethod("getCameraInfo", int.class, cameraInfoCalss);
                getCameraInfo.invoke(null, i, cameraInfo);

                if (cameraInfo == null)
                {
                    continue;
                }

                Field field = cameraInfoCalss.getDeclaredField("facing");
                int facing = field.getInt(cameraInfo);

                if (facing == backFacing)
                {
                    backId = defaultId;
                    defaultId++;
                }
                else if (facing == frontFacing)
                {
                    frontId = defaultId;
                    defaultId++;
                }
            }

            Method openMethod = cameraClass.getMethod("open", int.class);

            if (backId != -1)
            {
                //默认使用后置摄像头
                camera = (Camera) openMethod.invoke(null, backId);
            }
            else if (frontId != -1)
            {
                camera = (Camera) openMethod.invoke(null, frontId);
            }
        }
        catch (NoSuchMethodException e)
        {
            e.printStackTrace();
        }
        catch (InvocationTargetException e)
        {
            e.printStackTrace();
        }
        catch (IllegalAccessException e)
        {
            e.printStackTrace();
        }
        catch (InstantiationException e)
        {
            e.printStackTrace();
        }
        catch (NoSuchFieldException e)
        {
            e.printStackTrace();
        }

        if (camera == null)
        {
            //若为空,使用默认方法打开一次
            camera = Camera.open();
        }

        return camera;
    }