Single-Stage vs Two-Stage Animation for iPhone Apps?

Question

What are single-state and two-stage animation for rotating an iPhone window?

This is the \"error\" message I get in the Debugger Console (nothing crashes):

Answer 1

I changed from willAnimateFirstHalfOfRotationToInterfaceOrientation:duration: method to willAnimateRotationToInterfaceOrientation:duration: method and warning gone.

Thanks.