C# Delegates vs. Interfaces: Understanding Their Distinct Roles

Explore the key differences between delegates and interfaces in C#. This comparison clarifies their distinct purposes—method references and callbacks vs. contracts for class implementation—highlighting their respective strengths and appropriate usage scenarios in object-oriented programming.

Delegates vs. Interfaces in C#

Both delegates and interfaces are powerful tools in C#, but they serve very different purposes. Delegates are used for managing references to methods, enabling callbacks and event handling. Interfaces define contracts that classes must implement, promoting abstraction and code reusability.

Delegates in C#

A delegate is a type that holds a reference to a method. Think of it as a function pointer. You can assign methods to delegates, pass them as arguments to other methods, and invoke them dynamically. This is particularly useful for callbacks, event handling, and asynchronous operations.

Declaring a Delegate

delegate void MyDelegate(int x); //Declares a delegate that takes an int and returns void

Creating a Delegate Instance

MyDelegate myDelegate = MyMethod; //Assigns the method MyMethod to the delegate

Invoking a Delegate

myDelegate(10); // Invokes the method referenced by the delegate

Multicasting

A delegate can point to multiple methods (multicast delegate):

myDelegate += AnotherMethod; // Adds AnotherMethod to the invocation list

Common Uses of Delegates

• Callback Mechanisms: Passing methods as arguments.
• Event Handling: Responding to application events.
• Asynchronous Programming: Managing asynchronous method calls.
• LINQ: Defining custom filtering or sorting logic.

Interfaces in C#

An interface in C# is a reference type that specifies a contract. It defines a set of members (methods, properties, events, indexers) that a class must implement. Interfaces don't provide implementations; they only specify the interface.

Interface Declaration

public interface IMyInterface {
    void MyMethod();
    int MyProperty { get; set; }
}

Interface Implementation

public class MyClass : IMyInterface {
    public void MyMethod() { /*Implementation*/ }
    public int MyProperty { get; set; }
}

Key Features of Interfaces

• Abstraction: Hide implementation details; focus on functionality.
• Polymorphism: Treat objects of different types uniformly through a common interface.
• Multiple Inheritance: A class can implement multiple interfaces.
• Dependency Injection: Promote loose coupling in your code.

Example: Area Calculation

public interface IShape { double Area(); }
public class Circle : IShape { //Implementation of interface
    // ...
}
public class Rectangle : IShape { //Implementation of interface
    // ...
}

Key Differences: Delegates vs. Interfaces