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?

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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).