Tool to check whether iPhone app is backward compatible

I am developing an iPhone app that needs to be compatible with iOS 4.x as 开发者_如何学Cwell as iOS 3.x. Is there a tool that checks the code statically and informs me if a method/class isn't available in iOS 3.x? Classes like UIGestureRecognizer are available only on iOS 3.2 and higher.

Thanks in advance

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Though I haven't done this yet, this question looks very useful for this question: finding unsupported apis with os version

Hope this helps!