by
Felix Reidl | 21 November 2005In
the previous page, I explained one may of
making your functions modular, but I also introduced a lot of code. I will
explain what the code does on this page.
- class Player
extends MovieClip
- {
As explained above: we want our class to be able to control
the position of our MovieClip. The 'extends' keyword means that all functions
and variables from 'MovieClip' are inherited to our 'Player' class.
To easily assign a class to a MovieClip, bring up the
'Linkage Properties' and assign the class by entering it's name in the AS
2.0 Field.
- var action:Function;
- var animation:String;
-
- // constructor functions
- function Player()
- {
- action =
stand;
- animation =
new String();
- animation =
"stand";
- }
This part simply declares the member variables 'action' (as a
referrer to a function) and 'animation' (a String that contains the name of the
animation that should be played).
The function 'Player' is the constructor for our class, it's
called when an instance of the class is created (if you assign the class to a
MovieClip it is instanced when the MovieClip is loaded). We simply initialize
the variables here, most important the 'action'-referrer, as we will call it in
the 'update' function.
- function stand()
- {
- animation =
"stand";
-
- if (Key.isDown(Key.SPACE))
- return run;
-
- return stand;
- }
This is the first thing our Player can do – simply stand. And
he'll do it until the user presses the spacebar, in this case the function won't
return itself anymore but the 'run' function we'll handle next.
- function run()
- {
- animation =
„run“;
-
- _x +=
10;
-
- if (Key.isDown(Key.SPACE))
- return run;
-
- return stand;
- }
Now, the 'run'-function works similarly: as long as the user
presses space, our Player runs (and his position is increased by 10 units per
frame). If the user stops pressing space the function returns the referrer to
the 'stand'-function, the Player stops running.
Okay, this isn't a very fancy script. So what's the point?
Think about this: what if we want to integrate another function, 'jump()'? All
we have to do is write it and let the other functions return it if necessary!
If you want a little advanced example, download the class
file from the example animation on the previous
page. You'll also see why we have the variable named 'animation': it
tells us which animation is played and if it's the one that should be played.
Pros and Cons
This technique proved quite useful for me in the past. You have to try for
yourself if it suits you. But here are some pros and cons that might help you
decide:
Pros:
-
No complicated „if-else“ statements. The programming logic
is implicated in the return values.
-
Re-usable code. You can easily copy just one function and
fit it into another program.
-
Nice structured ActionScript.
Cons:
-
You must get used to it.
-
More function calls (as if that matters...).
-
Danger of redundant code. As there is only one function
called at a time, you might have to code the same things twice (i.e. Check
if the player hits an enemy, etc.) but that can be minimized by introducing
functions that are outside of the 'flow'.
I have provided the source files used for creating the example
animation you saw in the earlier page:

If you have any questions, feel free to post them on the
kirupaForums.
Good Luck!
 |
Felix Reidl |
 |
page 2 of 2 |
|
|