User Guide

198 ComboBox component

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

dispatches an event (in this case,

scroll) 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 component instance my_cb, the following example sends a message to the

Output panel that indicates the index of the item that the list scrolled to:

// Add Items to List.

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

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

my_cb.addItem({data:3, label:"Third Item"});

my_cb.addItem({data:4, label:"Fourth Item"});

// Display scroll bar if ComboBox has more than 2 items.

my_cb.rowCount = 3;

// Create Listener Object.

var cbListener:Object = new Object();

cbListener.scroll = function(evt_obj:Object) {

trace("The list had been scrolled to item # "+evt_obj.position);

};

// Add Listener.

my_cb.addEventListener("scroll", cbListener);