相機開發(先後攝像頭小筆記)

因爲應用支持Android 2.2 版本，因此直接使用Camera.open()打開Camera，但據反應在某些平板上無後置攝像頭但有前置攝像頭的時候，則沒法使用(由於open()方法只能打開後置攝像頭)。

故使用反射則中解決，默認使用後置。(在臺電平板上已測試經過)

/**
     * 打開默認相機
     * 默認打開後置攝像頭，若沒有則打開前置
     * @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");

            //獲取先後攝像頭默認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)
            {
                //默認使用後置攝像頭
                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)
        {
            //若爲空,使用默認方法打開一次
            camera = Camera.open();
        }

        return camera;
    }