SOLID & Design Patterns Interview Question #36

What is the difference between the Observer Pattern and C# events?

Structural, Creational & Behavioral Patterns Junior Beginner

Quick Interview Answer

Observer is the design concept: a publisher notifies interested subscribers about changes. C# events are a language mechanism that can implement that concept using delegates and controlled subscription.

Detailed Explanation

Observer can also be implemented with interfaces, reactive streams, message brokers, or other mechanisms. Therefore an event-based implementation is one form of Observer, not the definition of the pattern itself.

Code Example

orderService.OrderCreated += OnOrderCreated;

void OnOrderCreated(object? sender, Order order)
{
    Console.WriteLine($"Created: {order.Id}");
}