Thursday, April 14, 2011

[Tutorial] Common Design Patterns in C# 4.0
Part1: Introduction Gang of Four Design Patterns

Design Patterns provide standardized and efficient solutions to software design and programming problems that are re-usable in your code. Software Architects and developers use them to build high quality robust applications.

However, you have to take care to select the right pattern for the right problem. If you need to modify the initial pattern too much, this may indicate that it is not adapted to your needs and may in the worst case lead to unmaintainable, complex and inefficient code. The opposite of what you intend when using Design Patterns !!

You may also create your own custom Design Patterns. Whenever you come up with a certain solution that is reusable in a vast majority of your projects, you may decide to abstract a design pattern out of it. Then you may create your own library of patterns and share them within your whole company, thus creating standards and ameliorating maintainability.

In this series of blog posts I am going to show you how to use the well known Gang of Four (GoF) Design Patterns in C# 4.0 code. Those patterns will work well in any project that uses C# but especially in WPF, WCF, WinForms, ASP.NET projects.

The GoF Design Patterns are divided into 3 categories : Creational Patterns, Structural Patterns and Behavioral Patterns. In my following blog posts I am going to explain each GoF Design Pattern in detail and will show you examples of how to write good C# 4.0 code that implement those patterns.

Creational Patterns

  • Abstract Factory: Create instances of classes belonging to different families

  • Builder: Separate representation and  object construction

  • Factory Method: Create instances of derived classes

  • Prototype: Clone or copy initialized instances

  • Singleton: Class with only one single possible instance

Structural Patterns

  • Adapter: Match interfaces of classes with different interfaces

  • Bridge: Separate implementation and object interfaces

  • Composite: Simple and composite objects tree

  • Decorator: Dynamically add responsibilities to objects 

  • Facade: Class that represents subclasses and subsystems

  • Flyweight: Minimize memory usage by sharing as much data as possible with similar objects

  • Proxy: Object that represents another object

Behavioral Patterns

  • Chain of Responsibility: Pass requests between command and processing objects within a chain of objects

  • Command: Encapsulate a method call as an object containing all necessary information

  • Interpreter: Include language elements and evaluate sentences in a given language

  • Iterator: Give sequential access to elements in a collection

  • Mediator: Encapsulates and simplifies communication between objects

  • Memento: Undo modifications and restore an object to its initial state

  • Observer: Notify dependent objects of state changes

  • State:Change object behavior depending on its state

  • Strategy: Encapsulate algorithms within a class and make them interchangeable

  • Template Method: Define an algorithm skeleton and delegate algorithm steps to subclasses so that they may be overridden

  • Visitor:  Add new operations to classes without modifying them

There are also many other types of pattern such as: Parallel Patterns, SOA Patterns, Enterprise Architecture Patterns, etc… So if you work in the respective area don’t hesitate to look up patterns that may help you to be more efficient and build better applications.


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