ViewController

ViewController is a term used in Apple's Cocoa and Cocoa Touch frameworks to describe a controller object that manages a screen of content and mediates between the app’s data model and its user interface. In iOS development, the primary class is UIViewController, while macOS uses NSViewController. A view controller owns a root view and is responsible for loading, configuring, and presenting its subviews.

Core responsibilities include handling the view hierarchy, responding to user input, and coordinating with model objects. It participates in the view lifecycle, with methods such as loadView, viewDidLoad, viewWillAppear, viewDidAppear, viewWillDisappear, and viewDidDisappear. These callbacks allow developers to set up UI components, refresh data, and manage state as the user navigates through the app. Modern practice emphasizes keeping view controllers lightweight and delegating long-running tasks to other objects or background processes.

Navigation and presentation are common roles for view controllers. They can be embedded in navigation controllers to enable a push/pop stack, presented modally for temporary tasks, or used within container controllers like tab bars and split views. Transitions between view controllers can be performed programmatically or via storyboards using segues.

Interfaces are typically connected through outlets and actions, enabling UI components to interact with code without tight coupling. View controllers interact with models and other controllers to maintain synchronization between data and the user interface. While the term ViewController is most closely associated with iOS development, it embodies the broader MVC pattern where a controller coordinates a view and its underlying data.