render事件来提高程序的运行效率(as3.0)

public function addItem(item:DisplayObject):void {
	addChild(item);
	layoutContents();
}

package {
	
import flash.display.DisplayObject;
import flash.display.Sprite;
import flash.events.Event;

public class List extends Sprite {
	public function addItem(item:DisplayObject):void {
		addChild(item);
		layoutContents();
	}
	
	public function removeItem(item:DisplayObject):void {
		if(contains(item)) {
			removeChild(item);
			layoutContents();
		}
	}
	
	//对内部项目进行排列，可以是任意的排列算法
	protected function layoutcontents():void {
		trace("do layout");
		
		var y:Number = 0;
				
		var num:int = numChildren;
		for(var i:int=0; i<num; i++) {
			
			var child:DisplayObject = getChildAt(i);
			child.x = 0;
			child.y = y;
			
			y += child.height+2;
		}
	}
}

package {

import flash.display.Shape;

public class ListItem extends Shape {
	public function ListItem() {
		super();
		
		graphics.beginFill(0xFF6600);
		graphics.drawRect(0, 0, 30, 16);
		graphics.endFill();
	}
}
}

package {

import flash.display.Sprite;

public class ListTest extends Sprite {
	
	public function ListTest() {
		
		var list:List = new List();
		addChild(list);
		
		list.addItem(new ListItem());
		list.addItem(new ListItem());
		list.addItem(new ListItem());
		
	}
}
}