Guided course · Architecture and Design in .NET

Design Patterns in C#: The .NET Interview Guide: back to the course

Module 1 · Foundations: Patterns, SOLID and Judgment2 lessons

01Design Patterns in .NET Interviews: What They Are, the Patterns You Already Use, and How to Choose One
02SOLID in Modern C#: The Five Principles as the Foundation for Every Pattern, With a Real Refactor

Module 2 · Creational Patterns3 lessons

03Factory Method and Abstract Factory in C#: From switch Statements to Keyed Services in .NET 8 (included with Full Access)
04Builder and Prototype in C#: Fluent Builders, required and init, Records and the Shallow-Copy Trap (included with Full Access)
05Singleton in Modern .NET: Lazy<T>, DI Lifetimes, Captive Dependencies and Thread Safety (included with Full Access)

Module 3 · Structural Patterns4 lessons

06Adapter and Facade in C#: Wrapping Vendor SDKs, Callback APIs and Subsystems Behind Interfaces You Own (included with Full Access)
07Decorator in C# and .NET DI: Caching, Logging and Retry Without Touching the Class, Plus DelegatingHandler (included with Full Access)
08Proxy in C#: Protection, Virtual and Dynamic Proxies with DispatchProxy, and Where .NET Generates Them for You (included with Full Access)
09Composite in C#: Trees of Parts and Wholes, Product Bundles, Rule Trees, and Where .NET Uses It (included with Full Access)

Module 4 · Behavioral Patterns: Algorithms, State and Requests4 lessons

10Strategy in C#: Replacing switch Statements with Interchangeable Algorithms, DI Registries and Delegates (included with Full Access)
11Template Method in C#: Fixed Algorithms With Overridable Steps, BackgroundService, and When to Prefer Composition (included with Full Access)
12State Pattern in C#: Order Lifecycles, Invalid Transitions, and Transition Tables With Tuple Patterns (included with Full Access)
13Command Pattern in C#: Undo and Redo, Queued Commands With Channels, Idempotency and CQRS Commands (included with Full Access)

Module 5 · Behavioral Patterns: Communication and Pipelines4 lessons

14Observer in C#: Events, IObservable<T>, Safe Unsubscription, Handler Isolation and In-Process Domain Events (included with Full Access)
15Mediator in C# and MediatR: Requests, Notifications, Pipeline Behaviors, and When a Mediator Is Overkill (included with Full Access)
16Chain of Responsibility in .NET: ASP.NET Core Middleware, Short-Circuiting, Ordering and Handler Pipelines (included with Full Access)
17Visitor and Pattern Matching in C#: Double Dispatch, Expression Trees, ExpressionVisitor and Switch Expressions (included with Full Access)

Module 6 · Judgment, Practice and Mock Interview3 lessons

18When Not to Use Patterns: Anti-Patterns, Over-Engineering, and Modern C# Alternatives That Replace Them (included with Full Access)
19Design Patterns Practice Set: 10 Drills on Finding, Fixing and Choosing Patterns in Real C# Code (included with Full Access)
20Final Mock Interview: 25 Questions on Design Patterns, SOLID and Modern C# for .NET Interviews (included with Full Access)

Module 4 · Behavioral Patterns: Algorithms, State and Requests · Lesson 13 of 20

Command Pattern in C#: Undo and Redo, Queued Commands With Channels, Idempotency and CQRS Commands

17 min readTechInterviewNotes Editorial TeamUpdated 14 Oct 2026Save

This lesson comes with Full Access

Its text, video and cheat sheet open with Full Access. This course's free lessons open without an account. Start with Design Patterns in .NET Interviews: What They Are, the Patterns You Already Use, and How to Choose One.

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Practice

Practice test: Design Patterns in C#: Strategy, Template Method, State and Command — Lesson Practice8 questions · 15 minutes · 1 mark each, no negative marking

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PreviousState Pattern in C#: Order Lifecycles, Invalid Transitions, and Transition Tables With Tuple Patterns NextObserver in C#: Events, IObservable<T>, Safe Unsubscription, Handler Isolation and In-Process Domain Events

Practice test8 questions · 15 minutes · 1 mark each, no negative marking. Take it