Design Patterns



Design Patterns

Creational Patterns in C#

When it comes to asking questions about creating patterns with C#, Rajesh has all the answers. Read about some C# patterns in this article.

The software design patterns are mainly classified into three categories, namely Creational Patterns, Structural Patterns and Behavioral Patterns. The Creational Patterns deals with the best way to create objects. The Singleton Pattern is an example of Creational Pattern.

The singleton design pattern is used when only one instance of an object is needed throughout the lifetime of an application. The singleton class is instantiated at the time of first access and the same instance is used thereafter till the application quits.

The famous GOF defined the Singleton Pattern as follows.

“Ensure a class has only one instance, and provide a global point of access to it.” -- "Design Patterns” Gamma et al., Addison-Wesley, ISBN:0-201-63361-2”

The Singleton class can be used in various places where one would need a common repository of information that can be accessed from all objects in an application. For example sometimes we may need a single Database connection object or Network connection object.

Non-software Example

The office of the President of the United States is a Singleton. The United States Constitution specifies the means by which a president is elected, limits the term of office, and defines the order of succession. As a result, there can be at most one active president at any given time. Regardless of the personal identity of the active president, the title, "The President of the United States" is a global point of access that identifies the person in the office. [Michael Duell, "Non-software examples of software design patterns", Object Magazine, Jul 97, p54]

It is pretty easy to implement the Singleton Pattern in C#. There are lots trivial ways to achieve this. But by using a private constructor and a static method to create an instance of the class is a popular way to create singleton pattern.

Creational Patterns in C# - The Factory Method Pattern

The Factory Method Pattern comes under the classification of Creational Patterns. The creational patterns deals with the best way to create objects. The Factory Method provides a simple decision making class that can return the object of one of several subclasses of an abstract base class depending on the information that are provided.

“Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses.” -- "Design Patterns” Gamma et al., Addison-Wesley, ISBN:0-201-63361-2”

Non-software Example

Injection molding presses demonstrate this pattern. Manufacturers of plastic toys process plastic molding powder, and inject the plastic into molds of the desired shapes. The class of toy (car, action figure, etc.) is determined by the mold. [Michael Duell, "Non-software examples of software design patterns", Object Magazine, Jul 97, p54]

A factory pattern is one that returns an instance of one of several possible classes depending on the data provided to it. Usually all of the classes it returns should have a common base class and common methods, but implementations ...