Question

I am a developer working on a robotics application for iOS. I do not intend to submit this app to the app store, nor do I have any wish for suggested methods to be apple approved….

I am trying to get bluetooth working, and I think a good place to start is to try modifying the existing apple frameworks. Is it possible for me to modify the frameworks so that when they are built to my iOS device the frameworks will be modified for the app (but not other apps on the same device)?

Answer 1

As a matter of fact, you can!

Objective-C allows you to “swizzle” methods to override their default behavior, and yet still call the original implementation if you want to. You can do this for any number of Objective-C methods, as many times as you want.

If you wish to override behavior that is present in C functions, you will need a little bit more control over the platform. Jailbreaking allows you to use the full power of Jay Freeman’s CydiaSubstrate to hook or swizzle both Objective-C methods and C/C++ functions.

While I don’t recommend the use of MethodSwizzle per se, the following URL has a good discussion of swizzling http://cocoadev.com/wiki/MethodSwizzling.

But you should really use CydiaSubstrate’s MSHookMessageEx and MSHookFunction instead. Especially since you’re not submitting anything to the App Store.

Now regarding Bluetooth, I’ve done extensive work in this field (I developed Celeste, which is a systemwide tweak providing vanilla Bluetooth OBEX support to system apps on iOS). I suggest you look into using something like BTstack, which provides you with access to the bluetooth module from the HCI to RFCOMM levels, and supports things such as SDP and pairing, which you will probably need. It also has the added benefit of not requiring method swizzling, which some people seem to think is some sort of satanic ritual that should be avoided at all costs.