Observing the Observer Pattern

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Chris Missal, December 20, 2008

In my quest to improve my skills as a programmer, and moreover improve my understanding of patterns and practices, I wrote up a quick sample on the Observer pattern. At work, we're demoing a pattern a week to keep fresh on architectural principles. On Wednesday of this week, I presented a demo I wrote up that shows a simple example.

The code samples below are the basica concepts of the pattern. You have one object (the Observer) that "observes" a subject. The subject being observed in this code is an OrderService.

1 public interface IObserver
2 {
3     OrderService Subject { get; set; }
4 
5     void Update();
6 }
7

The OrderService should implement the IObservable interface:

1 public interface IObservable
2 {
3     void Attach(IObserver observer);
4 
5     void Detach(IObserver observer);
6 
7     void Notify();
8 }
9

To finish putting all the pieces together, we need our Subject, the OrderServce, to do something with the IObservable interface:

 1 public class OrderService : IOrderService, IObservable
 2 {
 3     public void Notify()
 4     {
 5         foreach (var observer in observers.Values)
 6         {
 7             observer.Subject = this;
 8             observer.Update();
 9         }
10     }
11 
12     public void Submit(Order order)
13     {
14         // do whatever the OrderService.Submit does..
15         Notify();
16     }
17 }

The OrderService Notifies its Observers when it Submits an Order. This pattern can take on many usages like firing events and works in a similar way as Messaging Systems.

To see the code view the SVN repository.

Filed Under: .Net C# Open Source Observer Pattern