The Decorator Pattern

The Decorator Pattern


The Decorator Pattern is a tool for dynamically modifying the behaviour of objects at runtime, promoting flexibility and reusability.

This pattern allows for attaching additional responsibilities to objects without altering their structure, making it a versatile and adaptable design pattern.

Understanding the Decorator Pattern

The Decorator Pattern revolves around the concept of wrapping existing objects in additional layers of functionality, known as decorators.

These decorators can be stacked and chained to modify the behaviour of the underlying object without changing its code.

Benefits of the Decorator Pattern

The Decorator Pattern offers several advantages, including:

  • Dynamic Behavior Modification: It allows for dynamically modifying the behaviour of objects at runtime.
  • Flexibility: It promotes flexibility by enabling the addition of new behaviours without modifying existing classes.
  • Reusability: It promotes code reuse by enabling the creation of reusable decorators.
  • Encapsulation: It promotes encapsulation by encapsulating responsibilities within decorators.
  • Maintainability: It improves maintainability by decoupling the core functionality from its specific behaviour.
  • Transparency: It allows for transparent behaviour modification, enabling clients to interact with decorated objects as if they were the original objects.

Types of Decorator Patterns

The Decorator Pattern encompasses several variations, each with its specific characteristics:

  • Chaining: Allows multiple decorators to be chained together to create complex behaviour.
  • Intercepting: Allows for intercepting and modifying messages sent to objects.
  • Proxy: Allows for providing alternative implementations or hiding the true nature of an object.

Implementing the Decorator Pattern in C#

To illustrate the implementation of the Decorator Pattern in C#, consider a simplified scenario of adding logging functionality to text messages:

Base Component:

The base component represents the core functionality of sending text messages.

public interface IMessage
    void Send(string message);

Concrete Component:

The concrete component sends text messages without any logging.

public class SimpleMessage : IMessage
    public void Send(string message)
        Console.WriteLine($"Sending message: {message}");


The decorator adds logging functionality to messages.

public class LoggingDecorator : IMessage
    private IMessage message;

    public LoggingDecorator(IMessage message)
        this.message = message;

    public void Send(string message)
        Console.WriteLine($"Logging message: {message}");

Using the Decorator Pattern:

To use the decorator pattern for adding logging to text messages:

var message = new SimpleMessage();
var decorator = new LoggingDecorator(message);

decorator.Send("Hello, world!"); // Logs the message before sending it

This example demonstrates a basic implementation of the Decorator Pattern in C# for adding logging functionality to text messages. The decorator pattern can be extended to handle more complex behaviour modifications and scenarios.


The Decorator Pattern is a valuable tool for dynamically enhancing the behaviour of objects at runtime, promoting flexibility, reusability, and maintainability in C# code.

It allows for creating adaptable and scalable software systems that respond to changing requirements without extensive code modifications.

By leveraging the Decorator Pattern, developers can build flexible, extensible, and maintainable applications.


Hi, my name is Stephen Finchett. I have been a software engineer for over 30 years and worked on complex, business critical, multi-user systems for all of my career. For the last 15 years, I have been concentrating on web based solutions using the Microsoft Stack including ASP.Net, C#, TypeScript, SQL Server and running everything at scale within Kubernetes.