The Flash Player APIs in ActionScript 3.0 contain many
classes that allow you to control objects at a low level. The architecture
of the language is designed to be more intuitive than previous versions.
While there are too many new classes to cover in detail here, the
following sections highlight some significant changes.
Note: Adobe® AIR™ applications
can also use the Flash Player APIs.
DOM3 event model
Document Object Model Level 3 event model
(DOM3) provides a standard way of generating and handling event
messages so that objects within applications can interact and communicate,
maintaining their state and responding to change. Patterned after
the World Wide Web Consortium DOM Level 3 Events Specification,
this model provides a clearer and more efficient mechanism than the
event systems available in previous versions of ActionScript.
Events and error
events are located in the flash.events package. The Flash components
framework uses the same event model as the Flash Player API, so
the event system is unified across the Flash platform.
Display list API
The API for accessing the Flash Player and Adobe
AIR display list—the tree that contains any visual elements in the
application—consists of classes for working with visual primitives.
The
new Sprite class is a lightweight building block, similar to the
MovieClip class but more appropriate as a base class for UI components.
The new Shape class represents raw vector shapes. These classes
can be instantiated naturally with the new operator
and can be dynamically re-parented at any time.
Depth management
is now automatic and built into Flash Player and Adobe AIR, rendering
assignment of depth numbers unnecessary. New methods are provided
for specifying and managing the z-order of objects.
Handling dynamic data and content
ActionScript 3.0 contains mechanisms
for loading and handling assets and data in your application that
are intuitive and consistent across the API. The new Loader class
provides a single mechanism for loading SWF files and image assets and
provides a way to access detailed information about loaded content.
The URLLoaderclass provides a separate mechanism
for loading text and binary data in data-driven applications. The
Socket class provides a means to read and write binary data to server
sockets in any format.
Low-level data access
Various APIs provide low-level access to data
that was never before available in ActionScript. For data that is
being downloaded, the URLStream class, which is implemented by URLLoader,
provides access to data as raw binary data while it is being downloaded.
The ByteArray class lets you optimize reading, writing, and working
with binary data. The new Sound API provides detailed control of
sound through the SoundChannel and SoundMixer classes. New APIs
dealing with security provide information about the security privileges
of a SWF file or loaded content, enabling you to better handle security
errors.
Working with text
ActionScript 3.0 contains a flash.text package
for all text-related APIs. The TextLineMetrics class provides detailed
metrics for a line of text within a text field; it replaces the TextFormat.getTextExtent() method
in ActionScript 2.0. The TextField class contains a number of interesting
new low-level methods that can provide specific information about
a line of text or a single character in a text field. These methods
include getCharBoundaries(), which returns a rectangle
representing the bounding box of a character, getCharIndexAtPoint(),
which returns the index of the character at a specified point, and getFirstCharInParagraph(),
which returns the index of the first character in a paragraph. Line-level
methods include getLineLength(), which returns
the number of characters in a specified line of text, and getLineText(),
which returns the text of the specified line. A new Font class provides
a means to manage embedded fonts in SWF files.
