iPhone HUD style progress bar

I've been wanting to create a HUD style loading bar like the SMS app on the iPhone used to have but I don't know how to. I was wondering if anyone has done this before or if there is a tutorial somewhere for it? I just think it looks so nice and w开发者_StackOverflow社区ould like to use it rather than the built in loading progress bar.

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It should be very simple to implement using Core Animation layers (the CALayer class).

The bar would be a layer with rounded corners and the fill could be drawn by a custom drawing method.