Turnable UIButton

I'm looking for some poin开发者_StackOverflow社区ters on how to create a turnable button like the knobs in garageband (iPad). I want to use this for a custom volume knob.

Thanks in advance!

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Like this: IPhone two fingers twist gesture ?

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It is too late, may be you have already found the answer! but I made this knob after getting inspired by garage band. Hopefully it will help you or any new members.

https://github.com/Krutarth/KnobGarageBandStyle

Enjoy!