[flexcoders] Binding using as3

[aceoohay]

I have customized textinput control with a property of x. In my program I 
instntiate the control as vtiA. My program has a bindable variable called _y.

I would like everytime that _y is changed by my program that the property x of 
the control vtiA reflects the new values.

What I have done that does not work is

[Bindable] private var _y;

private function whocares():void
{
    var vtiA:MyTextInput = new MyTextInput;
    vtiA.x = _y
}

If this were mxml I would just say 

<xx:MyTextInput id="vtiA" x="{_y}"/>

What is the equivalent in as3?

Paul