Macromedia flex 2 Manual

38

Creating Custom Events

Dispatching custom events

Flex defines many of the most common events, such as the 

click

 event for the 

Button

 

control, however, your application may require that you create events. In your custom Flex 
components, you can dispatch any of the predefined events inherited by the component from 
its superclass, and dispatch new events that you define within the component. 

To dispatch a new event from your custom component, you must do the following:

1.

(Optional) Create a subclass from the 

flash.events.Event

 class to create an event class that 

describes the event object. For more information, see 

.

2.

(Optional) Use the 

[Event]

 metadata tag to make the event public so that the MXML 

compiler recognizes it. For more information, see 

3.

Dispatch the event using the 

dispatchEvent()

 method. For more information, see 

Creating a subclass from the Event class

All events use an event object to transmit information about the event to the event listener, 
where the base class for all event objects is the 

flash.events.Event

 class. When you define a 

custom event, you can dispatch an event object of type Event, or you can create a subclass of 
the Event class to dispatch an event object of a different type. You typically create a subclass of 
the Event class when your event requires you to add information to the event object, such as a 
new property to hold information that the event listener requires.

For example, the event objects associated with the Flex 

Tree

 control include a property named 

node

, which identifies the node of the Tree control associated with the event. To support the 

node

 property, the Tree control dispatches event objects of type TreeEvent, a subclass of the 

Event class. 

Within your subclass of the Event class, you can add properties, add methods, set the value of 
an inherited property, or override methods inherited from the Event class. For example, you 
might want to set the 

bubbles

 property to 

true

 to override the default setting of 

false

, 

which is inherited from the Event class. 

You are required to override the 

Event.clone()

 method in your subclass. The 

clone()

 

method returns a cloned copy of the event object by setting the 

type

 property and any new 

properties in the clone. Typically, you define the 

clone()

 method to return an event instance 

created with the 

new

 operator.