What Is a Flash
MX Component?
by Colin Moock,
author of:
ActionScript for Flash MX: The Definitive Guide, 2nd Edition
Last March Macromedia released Flash MX with a compelling new
vision for the product: the animation and design software would
henceforth be groomed as a rich Internet application platform.
Accordingly, some heavy changes were made to the authoring environment.
Macromedia added an extensible library of user interface widgets,
known as the Flash UI Components, for quickly creating
common GUI applications. (Previously, Flash developers were
expected to bake all UI in their own ovens.) Java developers
accustomed to working with Swing or Visual Basic developers
used to a drag-and-drop environment will appreciate this critical
step in the direction of rich application development for the
Web.
Flash UI Components are actually a specific example
of the more general Flash MX component architecture. A component
in Flash MX is a reusable, packaged module that adds a particular
capability to a Flash movie. Components can include graphics
as well as code (as do the built-in Flash UI Components),
so they're neat little bundles of self-contained functionality
that you can easily drop into your projects. For example,
a component can be a radio button, a dialog box, a preload
bar, or even something that has no graphics at all, such as
a timer, a server connection utility, or a custom XML parser.
From a technical point of view, a component
is Flash MX's version of Flash 5's smart clip, which is a
movie-clip symbol that allows its variables (or "clip parameters")
to be set via a GUI in the authoring tool. Flash MX components
are typically subclasses of the built-in MovieClip
class, but they're not required to be. As such, they have
all the properties and methods of MovieClip, plus their
own properties and methods. (For the uninitiated, a MovieClip
is Flash's basic content container, something like a DHTML
layer in a web page.)
So the answer to "what is a Flash MX component?" depends partly
on your point of view. From a traditional Flash point of view,
components are effectively ready-made movie clips that you
install and drag into your movies. From a programmer's point
of view, components are customizable building blocks that
can be added to an application visually or programatically
and then wired into the application's logic and data.
Flash MX components are Macromedia's effort to provide visual
programmers with a drag-and-drop development environment,
much like Microsoft Visual Basic. Using components you can
create a user interface visually in the Flash authoring tool
and then easily hook that interface up to routines that perform
some action. Figure 1 is a screenshot showing the creation
of a fill-in form with checkbox, listbox, and pushbutton components.
Figure 1. A fill-in form with checkbox, listbox, and pushbutton
components.
The component architecture is fully extensible. If you're
an advanced Flash developer, you can create your own components
and distribute them as binary files for other Flash developers
to install. The extensible component architecture allows Macromedia
to update the capabilities of Flash MX by shipping new component sets, without
requiring an updated version of the core authoring tool. Some
developers also use components to distribute code-only libraries
such as basic game classes or data-handling utilities. While
the use of components for code distribution is common practice,
the jury is still out on whether it is the best practice.
Flash MX does not impose a strict policy on code distribution.
Code can be distributed in a component, in a .as file
included in other .fla files, in a runtime or author-time
shared library, or in a .swf file that is dynamically
loaded at runtime. The distribution method you choose will
depend on your situation.
Chapter 14, "Movie Clip Subclasses and Components" and Chapter
16, "ActionScript Authoring Environment," of ActionScript
for Flash MX: The Definitive Guide describe how to create
components and explain how components work under the hood.
You can also check out Macromedia's online technotes:
Of course, the best way to learn about components is to
try them out. The following sites all have plenty of components
free for download:
You'll need the "Extension Manager" to install components
(which are distributed as .mxp files). You can get
the Extension Manager at the Macromedia
Flash Exchange.
Here are resources to learn how to use components to create
a GUI application:
Colin Moock has been researching,
designing, and developing for the Web since 1995.
Article originally published at http://www.oreillynet.com/pub/a/javascript/2003/01/28/actionscript.html
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