当被push时，ViewController会从屏幕的下方留下20px的白色。

I am using multiple controller during launch of an application in app delegate. One controller is for registration and the second controller is tabbar. tabbar was loading fine but when I pushed registration controller on window, contents went up by 20 units and I have good white blank screen at bottom. Therefore I recreated frame of my registration view controller in its viewdidload method and slided it 20 units down. The code is I am using multiple controller during launch of