getting label's height to determine it's y within a class

I got something like this:

var myClass:myClass = new myClass;
addChild(myClass.showLabel);

Then, inside this class there's this code:

public class myClass {
     private var myLabel:Label;
     private var myCanvas:Canvas;
     public function myClass() {
          myCanvas = new Canvas;
          myCanvas.width = 30;
          myCanvas.height = 30;
          myCanvas.x = 30;
          myCanvas.y = 30;
          myLabel = new Label;
          myCanvas.addChild(myLabel);
     }
     public function showLabel():Canvas {
          myLabel.text = 'example';
          myLabel.y = myCanvas.height/2 - myLabel.height/2;
          return myCanvas
    }

When debuging I see that 'myLabel.height' = 0. I don't know how to find it's final height. I was trying to use myCanvas.validateNow() before determining myLabel.y, but it didn't work.

This is a Flex project, but I don't think this matters.