There are a number of different ways to subscribe to events that are dispatched through the EventBus: The <code>EventBus</code> is used as a publish/subscribe event mechanism that lets objects communicate with eachother in a loosely coupled way.

The first is to listen to all events that are dispatched through the EventBus The <code>EventBus</code> is used as a publish/subscribe event mechanism that lets objects communicate with eachother in a loosely coupled way.. This is possible through the EventBus.addListener Adds a listener to the AppSettings. method. This method expects an IEventBusListener Interface to be implemented by all objects that want to register themselves as listeners to all events dispatched from the event bus. as an argument. The IEventBusListener Interface to be implemented by all objects that want to register themselves as listeners to all events dispatched from the event bus. looks like this:

public interface IEventBusListener {

 function onEvent(event:Event):void;

}

Every event dispatched by the EventBus The <code>EventBus</code> is used as a publish/subscribe event mechanism that lets objects communicate with eachother in a loosely coupled way. will be passed into the onEvent Handles an <code>Event</code> received from the event bus. method.

The second method is to only listen for events of a specific type. Use the EventBus.addEventListener Adds the given listener function as an event handler to the given event type. for this task. The addEventListener Adds the given listener function as an event handler to the given event type. method expects two arguments, the first is a string representing the event type, and the second is a Function instance which will be invoked with every event of the specified type.

Instead of a Function it is also possible to supply a proxy instead. This is what the addEventListenerProxy Adds a proxied event handler as a listener to the specified event type. method is for. Instead of a Function this expects a MethodInvoker instance. The MethodInvoker class is part of the as3-commons-reflect package.

The last option is to add a listener for events of a certain class. To get this to happen use the addEventClassListener Adds a listener function for events of a specific <code>Class</code>. or addEventClassListenerProxy Adds a proxied event handler as a listener for events of a specific <code>Class</code>. methods. The same arguments apply to these as for their addEventListener Adds the given listener function as an event handler to the given event type. and addEventListenerProxy Adds a proxied event handler as a listener to the specified event type. neighbours, except they expect a Class instance instead of a type.

All these methods naturally have a removal counterpart: removeListener Removes a listener from the AppSettings object., removeEventListener Removes the given listener function as an event handler from the given event type., removeEventListenerProxy Removes a proxied event handler as a listener from the specified event type., removeEventClassListener Removes a listener function for events of a specific Class. and removeEventClassListenerProxy Removes a proxied event handler as a listener for events of a specific <code>Class</code>..

To clear all types of registered eventlisteners at once simply call the removeAll() Clears the entire <code>IEventBus</code> by removing all types of listeners. method.

This is the easiest part, to dispatch an event through the EventBus The <code>EventBus</code> is used as a publish/subscribe event mechanism that lets objects communicate with eachother in a loosely coupled way. invoke either the dispatchEvent <p>When the <code>eventBusDispatching</code> property is set to <code>true</code> the specified <code>Event</code> will also be dispatched through the assigned <code>IEventBus</code> instance.</p> or dispatch Starts dispatching this event sequence. methods. The former expects an Event instance while the latter expects a string that indicates a certain type of Event. This event will be created by this method and subsequently dispatched. For example:

EventBus.dispatchEvent(new MyCustomEvent("myCustomEventType"));

or

EventBus.dispatch("myCustomEventType");

To prevent a lot of boilerplate code consisting of long lists of addEventListener* calls, Spring Actionscript includes an alternative way to define event handlers for events that are dispatched through the EventBus The <code>EventBus</code> is used as a publish/subscribe event mechanism that lets objects communicate with eachother in a loosely coupled way..

Instead of adding specific listeners functions through the addEventListener calls simply add a bit of metadata to the particular method:

[EventHandler]
protected function saveUserHandler(event:Event):void {
//implementation ommitted...
}

This is the most basic way of annotating a method and immediately implies certain assumptions. In this case it is assumed that the saveUser method will handle an event of the type "saveUser". Another valid method name for this handler could also be:

[EventHandler]
protected function saveUser(event:Event):void {
//implementation ommitted...
}

If, for some reason, this naming convention is not desired then add the name of the type of the specific event to the metadata:

[EventHandler(name="saveUser")]
protected function saveTheUserNow(event:Event):void {
//implementation ommitted...
}

By default, an event handler function is expected to have a single argument of type Event (or any subclass). It is however possible to let Spring Actionscript match the properties of the specified event with the arguments of the event handler. For instance, if the event passed to the saveUser event is not an ordinary event, but a subclass called SaveUserEvent with a property that is called "user" of the type "User". In this case an event handler with the following signature will work just a well:

[EventHandler]
protected function saveUser(user:User):void {
//implementation ommitted...
}

The property/argument matching is done by type, so this will fail in the case where an event has multiple properties of the same kind. If the SaveUserEvent should have two user properties, called userA or userB for example, the matching will fail. In that case it is possible to define the properties by name directly in the metadata:

[EventHandler(properties="userA,userB")]
protected function saveUser(userA:User, userB:User):void {
//implementation ommitted...
}

To annotate a handler for a certain event Class, define the fully qualified class name like this:

[EventHandler(clazz="com.classes.events.UserEvent")]
protected function saveTheUserNow(event:UserEvent):void {
//implementation ommitted...
}

To enable the processing of these kinds of annotations it is necessary to add an instance of the EventHandlerMetaDataPostProcessor to the application context. The easiest way to do so is to add this bit of XML to the configuration:

<object id="eventhandlerProcessor" class="org.springextensions.actionscript.ioc.factory.config.EventHandlerMetaDataPostProcessor"/>

This will automatically register the processor with the application context.

On the other side of the spectrum there is event dispatching and a way to avoid having to call EventBus.dispatch(someEvent) Starts dispatching this event sequence. a zillion times. For this particular goal there is the [RouteEvents] metadata which can be handled by the RouteEventsMetaDataPostProcessor. Let's take a look at simple example, imagine a class that is able to dispatch a number of events:

[Event(name="eventName1",type="...")]
[Event(name="eventName2",type="...")]
[Event(name="eventName3",type="...")]
public class MyClass {
  //implementation omitted..
}

To let Spring Actionscript catch all these events, and redispatch them through the EventBus The <code>EventBus</code> is used as a publish/subscribe event mechanism that lets objects communicate with eachother in a loosely coupled way., all that is necessary is the addition of the [RouteEvents] metadata:

[RouteEvents]
[Event(name="eventName1",type="...")]
[Event(name="eventName2",type="...")]
[Event(name="eventName3",type="...")]
public class MyClass {
  //implementation omitted...
}

If not all events need to be re-routed then use the 'events' argument of the [RouteEvents] metadata:

[RouteEvents(events="eventName1,eventName2")]
[Event(name="eventName1",type="...")]
[Event(name="eventName2",type="...")]
[Event(name="eventName3",type="...")]
public class MyClass {
  //implementation omitted...
}

And that's all there is to it, now to enable this functionality add this object definition to the XML configuration:

<object id="routeEventsProcessor" class="org.springextensions.actionscript.ioc.factory.config.RouteEventsMetaDataPostProcessor"/>

This will automatically register the processor with the application context.

The combination of the [RouteEvents] and [EventHandler] enables a developer to leverage the EventBus The <code>EventBus</code> is used as a publish/subscribe event mechanism that lets objects communicate with eachother in a loosely coupled way. without directly depending on it.

Leveraging the above described classes and techniques Spring Actionscript offers a small metadata driven MVC micro-framework. These are the key components that this framework provides:

The framework uses metadata tags in event and command classes to define mappings between them and the application context as a class factory for the commands.

<object id="mvcFactory" class="org.springextensions.actionscript.core.mvc.MVCControllerObjectFactoryPostProcessor"/>

[RouteMVCEvents]
[Event(name="someEventType","flash.events.Event")]
public class SomeClassThatDispatchesMVCEvents {
  //implementation ommitted...
}

[Command(eventType="someEventType")]
public class CommandClass {
  function execute():void {
    //implementation ommitted...
  }
  //further implementation ommitted...
}

[Command(eventClass="com.events.CustomEvent")]
public class CommandClass {
  function execute():void {
    //implementation ommitted...
  }
  //further implementation ommitted...
}

[Command(eventType="someEventType",executeMethod="process")]
public class CommandClass {
  function process():void {
    //implementation ommitted...
  }
  //further implementation ommitted...
}

[Command(eventType="someEventType",executeMethod="process")]
public class CommandClass {
  function process(event:Event):void {
    //implementation ommitted...
  }
  //further implementation ommitted...
}

public class CustomEvent extends flash.events.Event {
  public static const EVENT_ID:String = "someEventType";

  public var user:User;
  //further implementation ommitted...

}

[Command(eventType="someEventType",executeMethod="process")]
public class CommandClass {
  function process(user:User):void {
    //implementation ommitted...
  }
  //further implementation ommitted...
}

[Command(eventType="someEventType",executeMethod="process")]
public class CommandClass {

  public var user:User;

  function process():void {
    //implementation ommitted...
  }
  //further implementation ommitted...
}

[Command(eventType="someEventType",executeMethod="process",properties="userA,userB")]
public class CommandClass {

  function process(userA:User, userB:User):void {
    //implementation ommitted...
  }
  //further implementation ommitted...
}

<object id="myCommand" class="com.classes.commands.CommandClass"/>

[Component]
[Command(eventType="someEventType",executeMethod="process")]
public class CommandClass {
}