eventbrokerextensions.html

---
layout: documentation 
title: EventBroker 
teaser: Decoupled eventing with automatic thread switching
navigation:
   - name: Overview
     link: eventbroker.html
   - name: Tutorial
     link: eventbrokertutorial.html	
   - name: Registration by Attribute
     link: eventbrokerregistrationbyattribute.html
   - name: Registration over Interface
     link: eventbrokerregistrationoverinterface.html
   - name: Registration by Registrar
     link: eventbrokerregistrationbyregistrar.html
   - name: Simplified Handler Methods
     link: eventbrokersimplifiedhandlermethods.html
   - name: Direct Interaction
     link: eventbrokerdirectinteraction.html
   - name: Handlers
     link: eventbrokerhandlers.html
   - name: Matchers
     link: eventbrokermatchers.html
   - name: Exception Handling
     link: eventbrokerexceptionhandling.html
   - name: Extensions
     link: eventbrokerextensions.html
   - name: Logging
     link: eventbrokerlogging.html
   - name: Testability
     link: eventbrokertestability.html
   - name: Tips and Tricks
     link: eventbrokertipsandtricks.html
   - name: Specifications
     link: eventbrokerspecifications.html		 
---
<h2>Extensions</h2>
<p>
You can use extensions to add functionality to the event broker. 
Examples are the DistributedEventBroker (sending events over process boundaries) and MappingEventBroker (mapping event arguments to other types) extensions.
Extensions can also be used to implement logging or take control of exception handling. 
</p>
<p>
The event broker calls methods on each registered extension whenever something interesting happens like an object was registered, an event is fired or a handler throws an exception.
Extensions can be registered on the event broker:
</p>
<script type="syntaxhighlighter" class="brush: csharp"><![CDATA[
eventBroker.AddExtension(new MyExtension());
]]></script>

<h3>Use Extensions for Exception Handling</h3>
<p>
Extensions provide a simple way to take control over exception handling.
</p>
<script type="syntaxhighlighter" class="brush: csharp"><![CDATA[
public class MyExceptionHandlingExtension : EventBrokerExtensionBase
{
	public void SubscriberExceptionOccurred(
	     IEventTopicInfo eventTopic, 
		 Exception exception, 
		 ExceptionHandlingContext context)
	{
		/* do something with exception and if you can handle it 
		   then tell the event broker that exception is handled */
		context.SetHandled();
	}
}
]]></script>
<p>
When you call <code>SetHandled()</code> on the <code>context</code> then the event broker will not re-throw the exception.
</p>
<p>
The class <code>EventBrokerExtensionBase</code> simply implements all methods of <code>IEventBrokerExtension</code> with 
virtual methods so you only have to override the methods you are interested in.
</p>

<h3>Built-in extensions</h3>
<p>
Appccelerate contains the following extensions for the event broker:
<ul>
  <li><a href="distributedeventbroker.html">Distributed Event Broker</a>: Send events to other processes over WCF, NServiceBus, MassTransit or Rhino ESB</li>
  <li><a href="mappingeventbroker.html">Mapping Event Broker</a>: Map event arguments of an event onto another type of event arguments.</li>
  <li>Log4Net Logging Extension: logs everything happening on the event broker using log4net (available as source code package so you can adapt it to your needs easily.</li>
</ul>
</p>