What is Controller Object?

Answer

A controller object acts as a coordinator or as an intermediary between one or more view objects and one or more model objects. In the Model-View-Controller design pattern, a controller object (or, simply, a controller) interprets user actions and intentions made in view objects—such as when the user taps or clicks a button or enters text in a text field—and communicates new or changed data to the model objects.

 When model objects change—for example, the user opens a document stored in the file system—it communicates that new model data to the view objects so that they can display it. Controllers are thus the conduit through which view objects learn about changes in model objects and vice versa. Controller objects can also set up and coordinate tasks for an application and manage the life cycles of other objects. The Cocoa frameworks offer three main controller types: coordinating controllers, view controllers (on iOS), and mediating controllers (on OS X).