User Guide

184 ComboBox component

Using a dispatcher/listener event model, a component instance (comboBoxInstance)

dispatches an event (in this case,

itemRollOut) and the event is handled by a function, also

called a handler, on a listener object (

listenerObject) that you create. You define a method

with the same name as the event on the listener object; the method is called when the event is

triggered. When the event is triggered, it automatically passes an event object (

eventObject)

to the listener object method. Each event object has properties that contain information about

the event. You can use these properties to write code that handles the event. For more

information, see “EventDispatcher class” on page 499.

Finally, you call the

addEventListener() method on the component instance that

broadcasts the event to register the listener with the instance. When the instance dispatches

the event, the listener is called.

Example

With a ComboBox instance my_cb on the Stage, the following ActionScript sends a message

to the Output panel that indicates the item index and the event when the pointer rolls on or

off an item:

my_cb.addItem({data:1, label:"First Item"});

my_cb.addItem({data:2, label:"Second Item"});

// Create Listener Object.

var cbListener:Object = new Object();

cbListener.itemRollOver = function(evt_obj:Object) {

trace("index: "+evt_obj.index+", event: "+evt_obj.type);

};

cbListener.itemRollOut = function(evt_obj:Object) {

trace("index: "+evt_obj.index+", event: "+evt_obj.type);

};

// Add Listener.

my_cb.addEventListener("itemRollOver", cbListener);

my_cb.addEventListener("itemRollOut", cbListener);