package {
 
    import flash.display.Sprite;
    import flash.events.Event;
 
    public class Boxes extends Sprite {
 
        private var box:Box;
        private var boxes:Array;
        private var gravity:Number=0.1;
 
        public function Boxes() {
            init();
        }
 
        private function init():void {
            boxes = new Array();
            createBox();
            addEventListener(Event.ENTER_FRAME, onEnterFrame);
        }
 
        private function onEnterFrame(event:Event):void {
            box.vy+=gravity;
            box.y+=box.vy;
 
            //如果物体下落到了舞台(最下)边界，则再造一个出来往下掉
            if (box.y+box.height/2>stage.stageHeight) {
                box.y=stage.stageHeight-box.height/2;
                createBox();
            } else{
                for (var i:uint = 0; i < boxes.length; i++) {
                    //每个正在下掉的物体与其它物体做(矩形)碰撞检测
                    if (box!=boxes[i]&&box.hitTestObject(boxes[i])) {
                        box.y=boxes[i].y-boxes[i].height/2-box.height/2;
                        //堆到顶了，则停止
                        if (box.y<=box.height/2){
                            removeEventListener(Event.ENTER_FRAME,onEnterFrame);
                        }
                        else{
                            createBox();
                        }
                    }
                }
            }
             
        }
 
        private function createBox():void {
            box=new Box(Math.random()*40+10,Math.random()*40+10,Math.random()*0xffffff);
            box.x=Math.random()*stage.stageWidth;
            addChild(box);
            boxes.push(box);
        }
    }
}