导航弹出视图控制器时如何更改动画的方向

I want to change the direction when I pop a view controller. Below is the code I am using. I want to pop the controller from right (just a opposite direction when push a view controller) but it doesn't work. It just fade out gradually. How can I make the animation to be fading out from the right?I want to change the direction when I pop a vie