Question

Yesterday i gone through some article about EventAggregator, there some shot of code written like this,

(Message.Text as object).PublishEvent(PublishEventNames.MessageTextChanged);

 public static class ExtensionServices
    {
        //Supplying event broking mechanizm to each object in the application.
        public static void PublishEvent<TEventsubject>(this TEventsubject eventArgs, string eventTopic)
        {
            ServicesFactory.EventService.GetEvent<GenericEvent<TEventsubject>>()
                .Publish(new EventParameters<TEventsubject> { Topic = eventTopic, Value = eventArgs });
        }
    }

My question is, how the object got the method “PublishEvent”. Is my OOP understanding is wrong?

Answer 1

It was implemented as an Extension Method on the object class.

For example, this extension method (from the linked article):

public static class MyExtensions
{
    public static int WordCount(this String str)
    {
        return str.Split(new char[] { ' ', '.', '?' }, 
                         StringSplitOptions.RemoveEmptyEntries).Length;
    }
}   

Is defined on the String class (by using the this String syntax and a static method on a static class) .

In the project that this is defined in String now has a WordCount method (so long as it is also in the correct namespace).