How do you create a raised tab bar item, like is found in Instagram?

How do开发者_开发百科 you create a raised item within a UITabBar?

For example, Instagram has this:

How would I achieve something similar in my application?

iDevRecipes posted about how to go about recreating exactly that recently, although it's not written by Instagram's developers. Check out this post. The basic idea is that you create a custom UIButton then add it as a subview above the middle of the tab bar (the middle tab is a dummy tab bar item that does nothing).