Design Pattern description, which is one of the Design patterns.

1. Structural Pattern
DECORATOR
Mohammad Reda Katby
Solution Architect
MOHE

2. Definition
• Provide a way of attaching new state and behavior to an object dynamically.
• The object does not know it is being “decorated”, which makes this a useful
pattern for evolving systems.
• A key implementation point in the Decorator pattern is that decorators both
inherit the original class and contain an instantiation of it.

3. Description
The importance of this pattern is that:
• The original object is unaware of any decorations.
• There is no one big feature-laden class with all the options in it.
• The decorations are independent of each other.
• The decorations can be composed together in a mix-and-match fashion.

4. Design
• Component
• An original class of objects that can have operations added or modified (there may be more than one such
class)
• Operation
• An operation in IComponent objects that can be replaced (there may be several operations)
• IComponent
• The interface that identifies the classes of objects that can be decorated (Component is one of these)
• Decorator
• A class that conforms to the IComponent interface and adds state and/or behavior (there may be more than
one such class)

5. Design

6. Quiz
Pattern Elements
• IComponent
• Component
• Operation
• Decorator
• Client
Example Elements
• Any photo
• A plain photo
• To display a photo
• A tagged photo
• Creator of photos and tagged photos

7. Options
• Multiple components
• Different components that conform to the interface
• Multiple decorators
• Multiple operations

8. Use
• Fits well in the graphics world
• Used in System.IO.Stream
• Used in Screen Creation inWPF

9. Use
Use the Decorator pattern when…
• You have:
• An existing component class that may be unavailable for subclassing.
• You want to:
• Attach additional state or behavior to an object dynamically.
• Make changes to some objects in a class without affecting others.
• Avoid subclassing because too many classes could result.