I have not found great reference on some questions I have about
desiging classes and architecture around Flash's architecture. Partly
this involves not fully understanding how Flash loads classes:
1. Load/init ordering: When do classes load, and when do static
initializers execute? If a class has a static property that is
assigned outside a constructor, is this initialized when the class
loads (presumably frame 1?) or the first time it is accessed, or what?
If class A refers to a static property of class B, how do I ensure
that class B is initialized before class A? What if each class refers
to a static property of the other class? (These are somewhat silly
examples to illustrate the grey area I'm trying to root out.)
2. Timeline/clip context: I am looking for corrections to a few
asserstions here:
- "this" (always?) refers to a movie clip when the code is outside any
class; often the main movie when in the movie's timeline.
- "this" refers to an object when inside any class method, with one
exception, which is when defining a function within a method, like so:
function classMethod() {
var loader = new loadVars();
loader.onData = function(text) {
this.foo(); /// "this" here does not refer to our class, but as
far as I can tell, to nothing
}
}
- "this" is dynamic; within the same function, it may take on
different meanings at run time depending on where the function is
called. (In which case I'm fuzzy on when and what.)
3. Associating MovieClips and classes: Can a class simply extend
MovieClip? And what exactly is happening when a library symbol is
linked to a class, at runtime?
I tend to favor composition regardless, but there is something ugly to
me about having multiple classes which logically correspond to movie
clips in the library having to hard-code attachMovie(), which also
introduces an architectural problem that seems to break encapsulation.
If I have, for instance, 3 classes that handle different aspects of a
GUI, or perhaps sprites, and each class in its constructor uses
attachMovie() to create graphics from library symbols, if they all
attach to _root, then they must make sure to each use distinct depths,
which forces each class to know what depths the others are using (or
*always* using _root.getNextHighestDepth(), which isn't always
desirable). Alternatively, I could place container clips on the stage
at author time corresponding to each class, so depths are segregated
in this way, but this feels like its adding unnecessary complexity.
Finally, if a class uses a singleton pattern, where it has one and
only one static instance of itself, but also requires a movie clip, I
am confused as to when this instance gets added to the main timeline,
which then affects depth stacking order (see question #1).
Sorry the last is so verbose. I hope people can clear up my confusion...
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