eventbrokerregistrationbyattribute.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>Registration by Attribute</h2>
<p>
Registering events and event handler method with attributes is the simplest way to make events and event handler methods interact
with the event broker. However, there exist scenarios where attributes are not sufficient because only compile-time constant
values can be used in attribute definitions. For these dynamic scenarios see 
<a href="eventbrokerregistrationbyregistrar.html">registration by event broker registrar</a>.
</p>

<h3>Register Events and Handler Methods</h3>
<p>
The event broker listens to events with the attribute <code>EventPublication</code> and can call methods decorated with the 
<code>EventSubscription</code> attribute.
</p>
<script type="syntaxhighlighter" class="brush: csharp"><![CDATA[
public class MyClass
{
    [EventPublication("topic://SomeTopic")]
    public event EventHandler MyEvent;

    [EventSubscription("topic://SomeOtherTopic", typeof(OnPublisher))]
    public void HandleOtherTopic(object sender, EventArgs e)
    {
        // do something here
    }
}
]]></script>

<p>
After registration on the event broker, fired events are routed to corresponding subscribers.
</p>
<script type="syntaxhighlighter" class="brush: csharp"><![CDATA[
var eventBroker = new EventBroker();
var myInstance = new MyClass();

eventBroker.Register(myInstance);
]]></script>

<p>
If you want to stop interaction with event broker, you can unregister the instance from the event broker.
</p>
<script type="syntaxhighlighter" class="brush: csharp"><![CDATA[
eventBroker.Unregister(myInstance);
]]></script>

<h3>Event Topics</h3>
<p>
The string defined in the attributes is used to uniquely identify the event topic. 
Subscribers get notified about events fired with the same topic.
</p>

<h3>Signature</h3>
<p>
The event broker can only listen to events with an event handler type <code>EventHandler</code> or 
<code>EventHandler&lt;TEventArgs&gt; where TEventArgs : EventArgs</code>.
Other delegate types are not supported.
</p>
<p>
The signature of subscribers has to match the event handler type specified by the publication the subscriber listens to:
</p>
<script type="syntaxhighlighter" class="brush: csharp"><![CDATA[
event EventHandler Event  ->  void Handle(object sender, EventArgs e)

event EventHandler<MyEventArgs>  ->  void Handle(object sender, MyEventArgs e)
]]></script>

<h3>Handlers</h3>
<p>
You have to define how the event should be handled in the event subscription:
</p>
<script type="syntaxhighlighter" class="brush: csharp"><![CDATA[
[EventSubscription("topic://Topic", typeof(OnPublisher))]
]]></script>
<p>
See documentation about <a href="eventbrokerhandlers.html">handlers</a> for a list of available handlers.
</p>

<h3>Handler Restrictions</h3>
<p>
Handler restrictions (see <a href="eventbrokerhandlers.html">Handlers</a>) can be defined in the <code>EventPublication</code>:
</p>
<script type="syntaxhighlighter" class="brush: csharp"><![CDATA[
[EventPublication("topic://Topic", HandlerRestriction.Synchronous)]
[EventPublication("topic://Topic", HandlerRestriction.Asynchronous)]
]]></script>

<h3>Matchers</h3>
<p>
Publication or subscription specific matchers (see <a href="eventbrokermatchers.html">Matchers</a>) can be defined with the attributes:
</p>
<script type="syntaxhighlighter" class="brush: csharp"><![CDATA[
[EventPublication("topic://Topic", typeof(MyPublicationMatcher)]
[EventSubscription("topic://Topic", typeof(OnPublisher), typeof(MySubscriptionMatcher)]
]]></script>

<h3>Multiple Event Topics</h3>
<p>
You can fire multiple event topics or handle multiple event topics with a single event or event handler method:
</p>
<script type="syntaxhighlighter" class="brush: csharp"><![CDATA[
[EventPublication("Event1")]
[EventPublication("Event2")]
[EventPublication("Event3")]
public event EventHandler MultiplePublicationTopics;

[EventSubscription("Event1", typeof(OnPublisher))]
[EventSubscription("Event2", typeof(OnPublisher))]
[EventSubscription("Event3", typeof(OnPublisher))]
public void HandleMultipleSubscriptionTopics(
    object sender, 
    EventArgs e)
{
} 

]]></script>