UPDATE: There was a typo in the code section that adds the observer for NSUserDefaults. This has now been corrected. I also added information about how to find the proper assembly file when trying to access script class methods.

WARNING: The following is a technical article. Don’t blame me if you find it boring!

I love Unity! The Unity iPhone engine is a fantastic piece of technology, allowing us to quickly develop games without having to worry about a lot of the underlying stuff. However, Unity is essentially an additional layer on top of the iPhone SDK, which means that while the iPhone SDK may advance with new features, the Unity engine is generally a step behind with adding these features in a manner that can be easily accessed through script.

Enter Objective-C: This is the language that iPhone apps are usually written in. Unity provides some support for calling native Objective-C code from Unity script, but only for Advanced licensees and only in one direction. This can be pretty limiting especially if you’re trying to use a lot of the fancy features in iPhone OS 3.0. Sure, you can pass around information using the PlayerPrefs trick. But this has the problem of not being instantaneous, and it forces the app to constantly poll for new commands, which probably isn’t a good idea performance-wise.

What follows is a method for immediately calling Objective-C code from Unity script (for both Basic and Advanced licenses) and also vice versa! That’s right, two-way communication between Objective-C and Unity script that’s instantaneous.