ios7 view height error

ios7 view height error

Im playing with ios7 now, find that my view bounds became full screen eg.
before 320*460 now 320*480 with 20px status bar over my view, I know ios7
starts to support full screen layout, and has a
self.edgesForExtendedLayout = UIRectEdgeNone;
to set, but, this line seems work only when the navigation bar is shown,
i cant upload screenshots, and in ios6 view seems normal, and 320*460, in
ios7 its 320*480, status bar covers view contents, if I use a navigation
bar and set self.edgesForExtendedLayout = UIRectEdgeNone; view frame
became 320*416, leaves 20 for status bar and 44 for nav bar, but my app is
a custom top bar, not using navigation bar here.
if change the frame of window, window moves down by 20 px, but status bar
seems clipped and a black 320*20 bar is shown,
any method to make both iOS 6 and ios7 happy?