I'm trying to make an application that can share data between OS X and iOS using the multipeer connectivity framework. From what I understand I need two applications, one for OS X and one for iOS if I want them to communicate data both ways. Would they both have to be made with obj-c or can I make the iOS app using swift and the OS X with obj-c?
You can use either language on either platform. The multipeer framework can be called from Swift or Objective C and any combination will work.
In fact, it is possible to use the exact same code on both platforms by setting up a workspace with targets for iOS and OSX and common code included in both.