Friday, October 18, 2013

Introduction to ViewController in iOS

We follow MVC Pattern for development of iOS Application. Visit MVC Overview article on wiki to have a brief introduction to the pattern. It has been consumed neatly to implement the iOS applications.

ViewController Life Cycle

Life Cycle define how an object is created an lay out the different kind of stages it pass through before it gets to the end of the life cycle, also on course of the life it send different kind of events which other objects can observe. So what are different methods are involved in the ViewController life cycle? here is the brief introduction to each of them...
  • initWithNibName:bundle - Default Initializer of the view controller.
  • LoadView - Loads the view from the storyboard or the nib file.
  • viewDidLoad - After Initialization and all the outlets are set.
  • viewWillAppear - Called just before the view appear on the screen,.
  • viewWillDisappear - Called before the view disappear from the screen.
  • viewDidAppear and viewDidDisappear - After the view appear and disappear from the screen

Types of controller Objects

In Cocoa there are two types of controller objects. 
  • Mediating Controllers
  • Coordinating Controllers
Each controller is associated with different type of classes and provide different type of Behaviors.

Mediating Controllers

It is an Object that inherit from NSController class. These are used in the Cocoa binding technology. Mediating Controllers mediate the flow of data between the view objects and the model objects. 

Mediating controllers are generally controllers which we drag from the Interface Builder Library. You can configure these to establish binding between the view objects and the properties of the controller object. The abstract class NSController and its concrete subclasses NSObjectController, NSArrayController etc. provide features like supporting commit and discarding the changes.

Coordinating Controllers

A Coordinating Controller is typically an NSWindowController or NSDocumentController objects or Instance of a custom subclass of NSObject. Its role is to coordinated the functionality of the overall application or a part of the application. A coordinating controller provide features like:
  • Respond to Delegation messages or observing notifications
  • Respond to action messages
  • Managing the life cycle of owned objects.
  • Establishing connections between objects.
Instance of Custom NSObject subclass can be entirely suitable as coordinating controller. These kind of controller objects combine both mediating and coordinating functions. For mediating behavior they use mechanisms such as outlets, delegation, and notifications of the movement of data between view and the model. 

Just an overview of the controllers in iOS.

Happy Coding!!!

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