to be more complete how i would actually program it is like this :
import mx.utils.Delegate;
class CombinationHandler
{
// Declare the values used for each state
static var STATE_A:Number = 1; // 1 << 0
static var STATE_B:Number = 2; // 1 << 1
static var STATE_C:Number = 4; // 1 << 2
static var STATE_D:Number = 8; // 1 << 3
// Either declare the combinations here, or just use
// the STATE_A | STATE_B form in the declare handlers function
static var COMBINATION_AB:Number = STATE_A | STATE_B;
static var COMBINATION_BC:Number = STATE_B | STATE_C;
// array of functions to handle particular states
// and state combinations
private var handlers:Array;
public function CombinationHandler()
{
handlers = new Array();
createHandlers();
}
private function createHandlers()
{
// single case handlers
handlers[STATE_A] = Delegate.create(this,handleAOnly);
handlers[STATE_B] = Delegate.create(this,handleBOnly);
handlers[STATE_C] = Delegate.create(this,handleCOnly);
handlers[STATE_D] = Delegate.create(this,handleDOnly);
// combination handlers
handlers[COMBINATION_AB] = Delegate.create(this,ABhandler);
// OR
// handlers[STATE_A | STATE_B] = ...
}
public function handleUpdate(a:Object,b:Object,c:Object,d:Object)
{
// 'Digitise' the state from the selected flag in a,b,c,d.
var state:Number = (a.selected) | (b.selected << 1) |
(c.selected << 2) | (d.selected << 3);
// call the function
handlers[state]();
}
}
I think this way adding and modifying handlers is easy and safe, youre
not editing code thats surrounded by support code (like case:, else if
etc) so its clear where each response to a particular state is configured.
You can leave the declaration of the combinations out of the static
declarations at the top of the class like i said and just create the
combinations when defining the handler. That way when you add a
combination its just one place to edit, not two, but you may have a case
for using that information again so the static var could be useful. I
dont know :)
btw, in all the places you see | (bitwise OR) you can use + because it
works out the same, im just used to using the bitwise operators for
dealing with bit-based states and state masks. Similary for the shifts
(<<) you can change them for their equivalent multiplication.
thanks,
Martin
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