MVC and Decorator
Software Design Patterns
ABT1 Task 3
January 2015
A Basic MVC Pattern Example
MVC Component:
MODEL
 Data / Knowledge that represents an object
 Logic data often to update controller state
 Model can be a single object or many

MVC Component:
VIEW
 View: Represents the visual representation of the model data whether graphic, text, or other supported format.
 Presentation filer by revealing only what attributes are indicated
 Encapsulates data provided by model, by bringing it to life and displaying it to user
 View has to be aware of the attributes of a model by asking and receiving appropriate messages

MVC Component:
CONTROLLER
 Controller: Interacts with both model and view components by controlling the data flow into the model object.
 It is the link between a user and the system.
 Able to take model language and implement in view.
 Updates view when changes are present.
 Provides means by which a user can output by means of menus, buttons, mouse and other command and data avenues.
 Calls appropriate resources to carry out operations

Examples of MVC Applications
Websites
 Model: Data that controller will manage.
 View: Display requested data as indicated by user
 Controller: Manages user requests received as http or similar. Calls and coordinates resources to perform actions.
Calculator
 Model: input based on user interaction and requested data.
 View: Display screen of input and results of Model calculations.
 Controller: User interface buttons to enter numeric values and functions to send to Model.
A Basic Decorator Pattern Example
Decorator Pattern: Component and Decorator
 Component: Original programming or application before modification.
 Decorator: References and confirms component and interface relationship.
 Component is sub-classed into Decorator so all instances of original class are affected by Concrete Decorator change.
 OPEN CLOSE PRINCIPLE states that classes are open for extension but closed for modification thus Decorator Pattern addresses this issue.

Decorator Pattern:
Concrete Decorator and Concrete Component
 Concrete Decorator: used to override Component methods that need modification as result of a Decorator.
 Concrete Decorator: adds actual additional feature sets, function and responsibly to Component by overriding
 Concrete Decorators can be temporary and often referred to as WRAPPERS. Can be stacked and combined on a per user basis.
 Alternative to sub-classing which changes behavior at compile time, all instances of original class, whereas decoration institutes new behavior at runtime for individual objects.
 Concrete Component: is the implementation of the interface for the Component. Continues to be pointed to by Decorator and Component as additional functionality are stacked.

Examples of Decorator Pattern Applications
Cell Company Plans
 Component: SIM card programming designed to access network and initiate phone calls basic to all cell phones.
 Concrete Component: User interface as in phone OS and dialer.
 Decorator: Subclass of component acting as mediator between new features / plans and original basic operation.
 Concrete Decorator: To add features such as data for internet access, unlimited SMS, unlimited or specified data amounts. In any combination.
Weather Widgets
 Component: Weather application programming that accesses frequently updated weather database entries including allergy, wind, radar, etc...
 Concrete Component: User interface as in entry screen to customize city or specified data.
 Decorator: Subclass of component acting as mediator between new features and original operation.
 Concrete Decorator: Used to customize view, user experience and template design. Changes as necessary including Widget design. Customizable as application allows.
References