为ArrayCollection添加排序和获取数据

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute">
<mx:Script>
	<!--[CDATA[
		import mx.controls.AdvancedDataGrid;
		import mx.controls.Alert;
		import mx.messaging.AbstractConsumer;
		import mx.collections.Sort;
		import mx.collections.SortField;
		import mx.collections.ArrayCollection;
		
		private var coll:ArrayCollection=new ArrayCollection(
			[{name:"Tom",age:25},
			 {name:"Jim",age:15},
			 {name:"Lily",age:23}
			 ]);//创建一个集合
		public function init():void//初始化数据，绑定
		{
			
			 addItem();//调用添加函数
			 a.rowCount=coll.length;
			 
			 a.dataProvider=coll;//为DataGrid绑定数据源
			
		}
		
		public function addItem():void//为集合添加元素
		{
			var a:Object=new Object();//建立一个对象，插入到集合中
			a.name=t_name.text;
			a.age=t_age.text;
		
			coll.addItemAt(a,0);//a为插入的元素，0为插入的位置，也就是集合的开头			
		}
		
		public function checkItem():void//查找数据 
		{
			
			var sort:Sort=new Sort();//建立SORT对象
			var index:int;//用于显示集合索引号		
			sort.fields=[new SortField("age",true)];//按AGE进行排序
			coll.sort=sort;
			coll.refresh();	
			index=sort.findItem(coll.source,{name:t_name1.text,age:t_age1.text},Sort.ANY_INDEX_MODE);
			mx.controls.Alert.show("您找到的是"+index);
		    
			
			
		}
		
		
		
	]]-->
</mx:Script>	
	<mx:Canvas width="464" height="329" horizontalCenter="0" verticalCenter="0">
		<mx:DataGrid x="0" y="0" id="a" width="100%">
			<mx:columns>
				<mx:DataGridColumn headerText="name" dataField="name"/>
				<mx:DataGridColumn headerText="age" dataField="age"/>
			
			</mx:columns>
		</mx:DataGrid>
		<mx:Button label="添加" click="init()" bottom="10" left="97"/>
		<mx:TextInput x="47" y="237" id="t_name"/>
		<mx:TextInput x="47" y="267" id="t_age"/>
		<mx:Button label="查找" bottom="10" left="344" click="checkItem()"/>
		<mx:TextInput x="294" y="237" id="t_name1"/>
		<mx:TextInput x="294" y="267" id="t_age1"/>
		<mx:Text x="247" y="239" text="name:"/>
		<mx:Text x="247" y="269" text="age:"/>
		<mx:Text x="0" y="239" text="name:"/>
		<mx:Text x="0" y="269" text="age:"/>
	</mx:Canvas>
</mx:Application>

查找有点小问题，希望大家指教