ActionScript Calling Private Functions By Changing Public Variables?

Question

i've never tried to do this before, so my head a swimming a bit. i'd like to have a public boolean called enabled in myClass custom class. if it's called to be changed, how do i trigger a function from the change?

should i add an Event.CHANGE event listener to my variable? can i do that? or is there a more standard way?

Answer 1

We usually use properties for that.
Properties are just like public variables for the outside -- you can set instance.enabled = true; and so forth.. But you define properties as getters and/or setters functions for the class.
They are the perfect place for custom logic to be executed on value changes.

For example:

public class CustomClass {
    private var _enabled:Boolean = false;

    public function set enabled(value:Boolean):void {
        trace('CustomClass.enabled is now', value);
        this._enabled = value;
    }

    public function get enabled():Boolean {
        trace('CustomClass.enabled was retrieved');
        return this._enabled;
    }
}

Note that they can't have the same name as your private variable and you don't need both of them defined. Actually, you don't even need a variable for a setter/getter. You could use them just like any function -- they just supply you with a different syntax.
For example:

var object:CustomClass = new CustomClass();
object.enabled = false;
if (object.enabled) {
    ...
}

They are great to expose a simple API, keeping you from rewriting outside code if the class' internals have to change.

AS3 Reference on getters and setters.