iOS Components and Frameworks: Understanding the Advanced Features of the iOS SDK

Method Swizzling

The Objective-C runtime is flexible and provides support for dynamically changing object types and methods during execution of code. This support allows the developer to dynamically replace methods on existing classes, called method swizzling. Method swizzling can be used for a wide variety of use cases, but is typically most useful for replacing or augmenting existing methods on built-in classes where subclassing is not an option, or where using a category is not sufficient to achieve the desired results. For example, one project uses method swizzling to replace the setTitle: method on the UIViewController class to intelligently set either the title label or a custom image. Another project uses method swizzling to test whether ...