You've received a new requirement from your client. You've analyzed it, you know what needs to be done and how to do it. Now what? If you start coding right away, you're taking an unplanned approach.
Sure, you might finish and deliver the code, but will it be maintainable? Will it be reusable? Design patterns help you present your solution in a proven, structured way that promotes code reuse and maintainability. They don't give you the solution directly, but they help you organize the solution you already know into a better architecture.
Design patterns help you stick to object-oriented principles while solving common problems. For example, you need multiple entities in your program. Each entity should be independent, yet they need to communicate. How do you achieve this balance? Design patterns provide the answer.
When you use design patterns, you're not reinventing the wheel. You're applying solutions that have been tested and proven effective by countless developers. This leads to code that's easier to understand, maintain, and extend.
The most well-known design pattern is MVC—Model View Controller. This pattern is fundamental and serves as the basis for many modern frameworks like ASP.NET MVC and STRUTS.
View: Contains all your user interface code. View components are saved as .aspx files, .ascx files, and master pages. The view displays information to users and captures their input.
Model: Handles computational logic and business rules. Model components are typically classes saved in the App_Code folder. This is where data processing and business logic live.
Controller: Acts as a mediator between view and model. It receives user input from the view, processes it (often using the model), and updates the view with results. Controller components are saved as .cs files.
Let's look at how MVC works with a login screen:
MVC clearly separates your tasks into distinct components. When you need to change the UI, you only touch the view. When business logic changes, you only update the model. This separation means changes to one component don't ripple through your entire application.
Maintenance becomes easier because each component has a clear responsibility. Reusability improves because models can work with multiple views, and views can work with multiple models. Testing also becomes simpler because you can test components independently.
Design patterns fall into three main categories, each addressing different types of problems:
These patterns help you create instances of classes. Sometimes you don't know at compile time which instance you need to create—that decision happens at runtime. Creational patterns move instance creation logic into a separate "creator" class, keeping your code flexible.
Examples: Singleton, Factory, Abstract Factory, Builder, Prototype
These patterns deal with how you group classes and objects to form larger structures. Objects are generally grouped using composition—one object contains another. By grouping objects properly, you can easily establish communication between them.
Examples: Adapter, Bridge, Composite, Decorator, Facade, Flyweight, Proxy
These patterns focus on communication between objects. They define how objects interact and distribute responsibilities. Behavioral patterns help you manage complex control flows and handle varying behaviors.
Examples: Chain of Responsibility, Command, Interpreter, Iterator, Mediator, Memento, Observer, State, Strategy, Template Method, Visitor
There are 23 fundamental design patterns that form the basis for many other customized patterns. Here's how they're organized:
You don't need to memorize all 23 patterns immediately. Start with the most common ones you'll encounter in your daily work:
Study each pattern individually. Understand the problem it solves, see examples, and try implementing it yourself. Over time, you'll develop an intuition for which pattern fits which scenario.
Design patterns are essential tools for building maintainable, reusable software. They provide proven solutions to common design problems and help you write code that follows object-oriented principles.
The MVC pattern demonstrates these benefits clearly—by separating concerns into Model, View, and Controller, you create applications that are easier to maintain and extend. As you learn more patterns from the three categories (Creational, Structural, and Behavioral), you'll find yourself naturally applying them to solve design challenges in your projects.
Design patterns are proven solutions to common software design problems. They help you present solutions in a reusable, maintainable way while sticking to object-oriented principles. They provide a shared vocabulary for developers and promote best practices.
MVC (Model-View-Controller) separates an application into three components: View handles UI display, Model contains business logic and data processing, and Controller mediates between View and Model. This separation makes code more maintainable and allows changes to one component without affecting others.
The three categories are: Creational Patterns (help create instances of classes), Structural Patterns (organize classes and objects into larger structures), and Behavioral Patterns (establish communication between objects). Each category solves different types of design problems.
There are 23 core design patterns documented in the Gang of Four book. These patterns fall into three categories: Creational (5 patterns), Structural (7 patterns), and Behavioral (11 patterns). Many other customized patterns have evolved from these core patterns.