Design patterns in C# - Practical examples with diagrams

A hands-on collection of Gang of Four design patterns implemented in C# with Exalidraw diagrams and examples.
Perfect for .NET developers preparing for interviews, studying software architecture, or looking for clean, copy-paste-ready pattern implementations.

📋 Patterns Included

Creational Patterns

Pattern	Description	Code
Singleton	Ensures a single instance with global access point	singleton_pattern/
Factory Method	Delegates object creation to subclasses	factory_pattern/
Builder	Constructs complex objects step by step with validation	builder_pattern/

Structural Patterns

Pattern	Description	Code
Adapter	Makes incompatible interfaces work together	adapter_pattern/
Bridge	Decouples abstraction from implementation to avoid class explosion	bridge_pattern/
Composite	Composes objects into tree structures	composite_pattern/
Decorator	Adds behavior dynamically via wrappers	decorator_pattern/
Façade	Simplifies a complex subsystem behind a single interface	façade_pattern/
Proxy	Controls access to another object (includes Remote Proxy)	proxy_pattern/

Behavioral Patterns

Pattern	Description	Code
Strategy	Swaps algorithms at runtime via composition	strategy_pattern/
Template Method	Defines algorithm skeleton, lets subclasses fill in steps	template_method_pattern/
Observer	Notifies multiple objects when state changes	observer_pattern/
Command	Encapsulates requests as objects (supports undo/redo)	command_pattern/
State	Alters behavior based on internal state changes	state_pattern/
Iterator	Traverses collections without exposing internals	iterator_pattern/

Other Patterns

Pattern	Description	Code
Repository	Abstracts data access behind a clean interface	repository_pattern/

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⚡ Quick Start

git clone https://github.com/MarioCodes/csharp-design-patterns.git
cd csharp-design-patterns

Open any pattern folder in Visual Studio or VS Code and run the examples.

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🧠 Design Principles

These are the core SOLID and OOP principles applied throughout the examples:

• Identify the aspects of your application that vary and separate them from what stays the same
• Program to an interface, not an implementation
• Favor composition over inheritance - has-a may be better than is-a
• Strive for loosely coupled designs between objects that interact
• Classes should be open for extension, but closed for modification

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🤝 Contributing

Contributions are welcome! Here are some ideas:

• Add missing GoF patterns
• Improve or add new Excalidraw diagrams
• Translate descriptions to other languages

Just fork, make your changes, and submit a PR.

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📚 References

• Head First Design Patterns
• Refactoring Guru — Design Patterns
• Microsoft .NET Design Patterns

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📄 License

This project is licensed under the MIT License — see the LICENSE file for details.

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⭐ Found This Useful?

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