Detect iphone internet sharing bar visibility

on the iphone, when internet sharing is activated and another device开发者_Go百科 is connected, a bar appear under the status bar. It makes the current view of the active app go down for some more 20 pixels.

I'd like to rearrange controls in my view when this new bar appears.

How can i detect when it becomes visible?

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These other SO questions should point you down the right path:

How to position view below green bar during phone call?

Resize for in-call status bar?