Objection is a lightweight dependency injection framework for Objective-C for MacOS X and iOS. For those of you that have used Guice, Objection will feel familiar.
The basic idea is that dependency injection improves the modularity and testability of your code, but it also creates some extra work. To create an object, you must first create and wire up its dependencies (and their dependencies). A dependency injection framework addresses this by creating the dependent objects for you, based on a configuration (called a “module”) that you give it.