Christian Bale is one of the most committed character actors in the world. Whether he needs to starve himself for a role or build up huge amounts of muscle mass, he's happy to take on the challenge for the right part.
Because of that, everyone assumed Bale's long hair look in 2011 was for an acting part. They were wrong. He was just enjoying some chill-out time between big jobs and decided to let everything grow for a while.