AS1 OOP: Custom Classes with MovieClips
by senocular
Introduction
Classes can be created not only to hold and handle data and
information as scripted objects residing in memory, but also
to pose as controllers for movieclip objects on the screen.
What this means is that you can create a custom class in
Actionscript that can be used as the primary class of a
movieclip.
By default, all movieclips on the screen are instances of
the type MovieClip. They are based on the MovieClip class in
Actionscript and inherit methods and properties from the
MovieClip prototype (properties like hitTest and getDepth
etc.). To have your own classes work with movieclip
instances on the screen, you would want to have them extend
the MovieClip class.
There is only one little problem. Movieclip instances
aren't created like other object instances using new keyword
in combination with a class constructor. They are created
internally by Flash as they not only exist as containers for
information memory, but also as visual elements on the
screen. That requires more goings on than what's required
with normal object creation. Flash needs to get down and
dirty with the library and copying visual symbols on to the
timeline and so on. Because of that, your movieclip
extending class constructors can’t exactly be used to make a
movieclip instance in Flash. Those movieclips are only made
by Flash itself as commanded by the timeline or through the
use of dynamic movieclip creation functions like
duplicateMovieClip or attachMovie. So what is there to do?
Luckily, Actionscript provides you a method for telling
Flash that it may need to use a class other than MovieClip
when it creates movieclip instances on the screen. That way
every movieclip won’t be restricted to the same default
inheritance chain with the direct association to the
MovieClip class and you can have your own class pose as a
movieclip instance's primary class. The command that allows
for this is Object.registerClass.
