Flash CS3 Documentation

Using ActionScript 2.0 Components > Handling Component Events > Using listeners to handle events

Using listeners to handle events

The version 2 component architecture has a broadcaster/listener event model. (A broadcaster is sometimes also referred to as a dispatcher.) It is important to understand the following key points about the model:

• All events are broadcast by an instance of a component class. (The component instance is the broadcaster.)
• A listener can be a function or an object. If the listener is an object, it must have a callback function defined on it. The listener handles the event; this means the callback function is executed when the event occurs.
• To register a listener to a broadcaster, call the addEventListener() method from the broadcaster. Use the following syntax:

  componentInstance.addEventListener("eventName", listenerObjectORFunction);
  

• You can register multiple listeners to one component instance.

  myButton.addEventListener("click", listener1);
  myButton.addEventListener("click", listener2);
  

• You can register one listener to multiple component instances.

  myButton.addEventListener("click", listener1);
  myButton2.addEventListener("click", listener1);
  

• The handler function is passed an event object.

  You can use the event object in the body of the function to retrieve information about the event type, and the instance that broadcast the event. See About the event object.

• A listener object remains active until explicitly removed using EventDispatcher.removeEventListener(). For example:

  myComponent.removeEventListener("change", ListenerObj);
  

This section contains the following topics:

• Using listener objects
• Using the handleEvent callback function
• Using listener functions
• About scope in listeners

Flash CS3