当iphone设备方向朝上/朝下时，我可以判断它是风景还是肖像？

I got this code that if the device is in landscape left/right or upside down it rotates and shows another view controller. but if it´s in the orientation face up or face down, then how can I tell if it´s in landscape mode or portrait? cause I only want to rotate if it´s face up or down and in landscape modeI got this code that if the device is in landsc