Event model

The native EventTarget class is designated for dispatching and listening to events, and actual implementations may use it for implementing an hierarchic DOM event model.

In addition, the IEventTarget interface may be implemented instead of extending the EventTarget class.

Subclassing EventTarget

The following program demonstrates implementing a basic EventTarget subclass that is able to emit events:

/** My event */
[Event(name="act", type="Event")]
/** My Actor */
class Actor extends EventTarget {
    function m():void {
        this.emit(new Event("act"));
    }
}

Listening to an event

Subscribing to an event looks as follows:

actor.on("act", function() { trace("acting") });

Implementing an event class

Event constructors must always take the event name (“type”) as the first argument; any other arguments may follow. In the following code the user inherits the Event constructor.

class UserEvent extends Event {}

EventTarget implementation

It is a rare case for the user to need to implement their own EventTarget class: it may only arise if the user needs EventTarget to work with their own Document Object Model.

The “emit” method

The emit method is defined as follows:

[Limit("E extends Event*(this)")]
/**
 * Dispatches an event.
 */
function emit.<E>(e:E):boolean {
    // code
}

When the emit() method is used, it will force a new E(...) expression to be a correct Event object construction, by ensuring the first argument identifies a determined event type according to E.

The “on” method

The on method is roughly defined as follows:

[Limit("E extends Event(this)")]
/**
 * Registers an event listener.
 */
function on.<E>(type:E.name, listener:function(E.type):void) : void {
    //
}

The third parameter was omitted for clarity.