Design Patterns in C# (.NET). A Modern Approach

This book is a practical guide to applying design patterns in the C# and .NET ecosystem. Unlike abstract textbooks, the material is built on real-world examples from enterprise application development, web services, and Unity games. You will not just learn the 23 classic GoF patterns, but also understand how to adapt them to modern .NET realities (asynchrony, LINQ, DI containers).

Who this book is for

• Junior developers — to stop writing "spaghetti code" and master architectural thinking.
• Middle/Senior developers — to systematize knowledge and get acquainted with advanced techniques (e.g., patterns for microservices).
• Software architects — as a reference with ready-made solutions for typical tasks.

What you will learn

• How to distinguish the Factory Method from the Abstract Factory and choose the right option.
• Why "Singleton" is often considered an anti-pattern and how to implement it safely in multithreaded .NET applications.
• How to use the "Strategy" pattern for flexible algorithm replacement (e.g., in validation or sorting).
• Implementing the "Observer" pattern via C# events and Reactive Extensions (Rx.NET).
• Patterns for working with asynchrony: "Async Facade", "Object Pool", and "Concurrency Limiter".
• How patterns combine with SOLID principles and DI containers (Autofac, Microsoft DI).

Book structure

Each chapter is dedicated to one pattern and contains:

• The problem — a real scenario where the pattern is indispensable.
• A UML class and sequence diagram.
• A step-by-step implementation in C# with comments.
• An analysis of common mistakes and code smells.
• Exercises for reinforcement (with answers at the end of the book).

Why this book

Most materials on patterns are written for Java or C++. This book is fully adapted for .NET: you will learn how to use language features (properties, delegates, generics, async/await) to simplify implementation. At the end of the book, there is a bonus chapter with patterns for Entity Framework Core and ASP.NET Core.

The book is suitable both for self-study and for preparing for interviews for a .NET developer position. After reading it, you will be able to design systems that are easy to extend and maintain.