User Guide

358 Chapter 6: Components Dictionary
Usage 2:
listenerObject = new Object();
listenerObject.change = function(eventObject){
...
}
chooserInstance.addEventListener("change", listenerObject)
Description
Event; broadcast to all registered listeners when a date is selected.
The first usage example uses an
on() handler and must be attached directly to a DateChooser
instance. The keyword
this, used inside an on() handler attached to a component, refers to the
component instance. For example, the following code, attached to the date chooser
myDC, sends
“_level0.myDC” to the Output panel:
on(change){
trace(this);
}
The second usage example uses a dispatcher/listener event model. A component instance
(
chooserInstance) dispatches an event (in this case, change) 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.
Finally, you call the
EventDispatcher.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.
For more information, see “EventDispatcher class” on page 415.
Example
This example, written on a frame of the Timeline, sends a message to the Output panel when a
DateChooser instance called
myDC is changed. The first line of code creates a listener object called
form. The second line defines a function for the change event on the listener object. Inside the
function is a
trace() statement that uses the event object that is automatically passed to the
function, in this example
eventObj, to generate a message. The target property of an event
object is the component that generated the event (in this example,
myDC). The
NumericStepper.maximum property is accessed from the event objects target property. The last
line calls
EventDispatcher.addEventListener() from myDC and passes it the change event
and the
form listener object as parameters.
form.change = function(eventObj){
trace("date selected " + eventObj.target.selectedDate);
}
myDC.addEventListener("change", form);