Dynamically generating tweened animations with actionscript is wonderful. Here is an example of code for an object that fades out over 0.5 seconds.

----- excerpt from custom class IndicatorLine.as ----- 

    _tween = new Tween(
        this, // object to change property of
        "alpha",// property to change
        Regular.easeIn,// ease formula
        1, // from
        0, // to
        0.5, // duration
        true // use seconds for duration
    );

One hurdle that tied me up for a while was the inability to coordinate an abstract property or several properties at once, such as the height of a bouncing ball or the status of a dynamic animation.

I found the solution. Here is a demonstration of the effect.

download source files: firecrow_as3_bouncing_ball_example.zip

The ball is beeing tweened on two levels at once. The first beeing the x position for the up and down motion of the bounce, and the second beeing the bounce height which smoothely transitions to match the value of the slider.

I found the solution when, out of curiosity, I read the source code for the fl.transitions.Tween package. The solution is simple, the property is dynamically assigned as a string, which means any get/set method can be used.

----- excerpt from Flash CS3 lib fl.transitions.Tween -----

    public class Tween extends EventDispatcher
    {
    ...

       /**
        * constructor function sets up an on EnterFrameListener
        * which calls "setPosition" to increment the property (prop)
        * util it reaches the specified value
        */
       function Tween(obj:Object, prop:String,...)
       {
       ...

           public function setPosition(p:Number):void 
           {   
               ...
               // p is the value of the next frame for prop
               this.obj[this.prop] = p;
              ...
           }   
       }
    }

Getter and setter are my new favorite thing for making methods that can be called like a property.

----- excerpt from custom class Bounce.as -----

        public function get distance():Number
        {   
            return _distance;
        }

        public function set distance(distance:Number):void
        {   
            _distance = distance;
        }

        /**
         * note: in this case the set mothod is not really necessary
         * but it can be a great source of adding behaviour to the 
         * setting of a property, such as to redraw the object 
         * when a property is changed
         */

And then that property name can be fed into the tween.

----- excerpt from custom class Stage.as ----- 

            _bounceDistanceTween = new Tween(
                ...
                "distance", // property to adjust on object
                ...
                );

The effect is that the Tween instance will update the property calling the set method with each value for a frame during the specified duration.

----- sample code -----

    /**
     * as if this is beeing excecuted
     */
    bounce.distance = value