setChildIndex改变flex组件的显示层次

import flash.display.Sprite;
import flash.events.MouseEvent;

var container:Sprite = new Sprite();
addChild(container);

var circle1:Sprite = new Sprite();
circle1.graphics.beginFill(0xFF0000);
circle1.graphics.drawCircle(40, 40, 40);
circle1.addEventListener(MouseEvent.CLICK, clicked);

var circle2:Sprite = new Sprite();
circle2.graphics.beginFill(0x00FF00);
circle2.graphics.drawCircle(100, 40, 40);
circle2.addEventListener(MouseEvent.CLICK, clicked);

var circle3:Sprite = new Sprite();
circle3.graphics.beginFill(0x0000FF);
circle3.graphics.drawCircle(70, 80, 40);
circle3.addEventListener(MouseEvent.CLICK, clicked);

container.addChild(circle1);
container.addChild(circle2);
container.addChild(circle3);
addChild(container);

function clicked(event:MouseEvent):void {
var circle:Sprite = Sprite(event.target);
var topPosition:uint = container.numChildren - 1;
container.setChildIndex(circle, topPosition);
}