C# - Differences Between Interfaces and Delegates

In C#, both interfaces and delegates are powerful tools, but they serve very different purposes. If you’re unsure when to use which, this guide will help you understand their differences and make the right choice for your code.

Key Differences Between Interfaces and Delegates

When to Use Interfaces

Use interfaces when:

• You need a contract: When you want to enforce a specific structure or behavior across multiple classes.
• You want polymorphism: When you need to treat objects of different classes as the same type.
• You need multiple inheritance: When a class must implement multiple contracts.

Example:

public interface IShape
{
double CalculateArea();
}

public class Circle : IShape
{
public double Radius { get; set; }

public double CalculateArea()
{
	return Math.PI * Radius * Radius;
}
}

When to Use Delegates

Use delegates when:

• You need callbacks: When you want to pass methods as parameters or notify other parts of your code.
• You’re handling events: When you want to implement event-driven programming.
• You need dynamic method invocation: When you want to decide which method to call at runtime.

Example:

public delegate void MyDelegate(string message);

public class MyClass
{
public void ShowMessage(string message)
{
	Console.WriteLine(message);
}
}

// Usage
MyDelegate myDelegate = new MyClass().ShowMessage;
myDelegate("Hello, Delegate!");

Summary

- Use interfaces when you need to define a contract or enable polymorphism.
- Use delegates when you need callbacks, event handling, or dynamic method invocation.

By understanding these differences, you can choose the right tool for your specific scenario and write cleaner, more maintainable code in C#.