Help. Some class methods not getting called

I'm in the process of writing my first ActionScript class and have run into a problem where two of my defined methods aren't getting called. Could some kindly guru take a look and point out what I'm doing wrong?

Thanks,

Ken

P.S. the purpose of this class is to encapsulate drag behavior.

// in action layer
Dragger = function(x, y, timeline, graphicID, depth)
{
this.x = x;
this.y = y;
this.timeline = timeline;
this.graphic = this.attachGraphic(graphicID, depth);
trace(this.graphic);
this.scale = 100;
this.wasDragged = false;
this.render();
}

Dragger.prototype.attachGraphic = function (graphicID, depth)
{
var newName = graphicID + "_" + depth;
this.timeline.attachMovie(graphicID, newName, depth);
return this.timeline[newName];
}

Dragger.prototype.render = function()
{
with (this.graphic)
{
_x = this.x;
_y = this.y;
}
}

// the next two methods don't seem to get called as their embedded messages never appear in the trace window
Dragger.prototype.onPress = function()
{
trace("item pressed");
}

Dragger.prototype.onRelease = function()
{
trace("item released");
}

this.timeline.addListener(this);


// in test layer
obj = new Dragger(0,0,this,"circleMC",100);

// this.graphic renders to stage OK

// clicking in the shape defined by this.graphic produces no output

Try this after your class declaration:

Dragger.prototype = new MovieClip();

or (I think) after you instantiate the class:

obj.prototype = new MovieClip();

The point is I'm pretty sure onPress handlers only apply to mc's and buttons.