Understanding Delegates in .NET Core: Types, Scenarios, Pros & Cons

Understanding Delegates in .NET Core: Types, Scenarios, Pros & Cons

Delegates are one of the core building blocks of the .NET platform, enabling flexibility and extensibility in a clean and type-safe manner. In this blog, we’ll break down what delegates are, their types, practical scenarios where you can use them, and the pros and cons of using them in .NET Core applications.

 

What is a Delegate?

A delegate in .NET is a type that encapsulates a reference to a method. Delegates are similar to function pointers in C or C++, but are type-safe and secure. They are mainly used to define callback methods and implement event handling.

Example:

public delegate int Calculate(int x, int y);

 

public class MathOperations {

    public int Add(int a, int b) => a + b;

    public int Subtract(int a, int b) => a - b;

}

 

// Usage

MathOperations math = new MathOperations();

Calculate calc = new Calculate(math.Add);

int result = calc(5, 3); // Output: 8

 

Types of Delegates in .NET Core

1. Single-cast Delegate

Points to a single method.

Action sayHello = () => Console.WriteLine("Hello!");

sayHello();

2. Multi-cast Delegate

Points to multiple methods using +=.

Action greet = Method1;

greet += Method2;

greet(); // Invokes both Method1 and Method2

3. Func<> Delegate

Built-in delegate that returns a value.

Func<int, int, int> add = (x, y) => x + y;

4. Action<> Delegate

Built-in delegate that returns void.

Action<string> print = (msg) => Console.WriteLine(msg);

5. Predicate<> Delegate

Built-in delegate that returns a boolean.

Predicate<int> isEven = x => x % 2 == 0;

 

Scenarios Where Delegates Are Used

1. Event Handling

Used in building UI or in custom event-driven systems.

public delegate void Notify();

public event Notify OnProcessComplete;

2. Callbacks in Async Programming

Delegates can be passed as parameters to methods and used as callbacks.

3. LINQ Expressions

Delegates are used extensively in filtering, projecting, and querying collections.

4. Strategy Pattern

Change logic at runtime by assigning different methods.

5. ASP.NET Core Middleware

The RequestDelegate type represents a function that can process HTTP requests.

 

Pros of Using Delegates

• Type-Safe: Catches errors at compile-time.
• Flexible and Dynamic: Assign methods dynamically.
• Multicasting Support: Chain multiple methods.
• Helps in Decoupling: Reduces tight coupling between components.

 

Cons of Using Delegates

• Harder to Debug: Debugging delegate chains can be tricky.
• Memory Leaks: Risk if event handlers aren’t unsubscribed.
• Readability: Can reduce readability if overused.
• Slight Overhead: Slight performance hit compared to direct method calls.

 

Real-World Uses in .NET Core

Scenario	Use of Delegate
ASP.NET Core Middleware	RequestDelegate processes HTTP requests.
Event-Driven Architecture	Delegates define and invoke events.
Strategy Pattern via DI	Inject behavior using Func<>, Action<>.
Background Tasks	Used in configuring jobs and retries.
LINQ Queries	Built-in delegates (Func<>, Predicate<>) for filtering data.

 

Conclusion

Delegates are essential for writing clean, flexible, and decoupled code in .NET Core. Whether you're building a scalable web app or a complex event-driven system, understanding delegates gives you a robust tool to improve your application's architecture.