flex计算器

<?xml version="1.0" encoding="utf-8"?>
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009" 
			   xmlns:s="library://ns.adobe.com/flex/spark" 
			   xmlns:mx="library://ns.adobe.com/flex/halo" minWidth="1024" minHeight="768" xmlns:tudou="components.*">
	<fx:Declarations>
		<!-- Place non-visual elements (e.g.,services,value objects) here -->
	</fx:Declarations>
	<fx:Script>
		<![CDATA[
			import mx.collections.ArrayCollection;
			import mx.controls.Alert;
			private var mydp:ArrayCollection=new ArrayCollection([
				{text:"加法",value:"+"},{text:"减法",value:"-"},{text:"乘法",value:"*"},{text:"除法",value:"/"}
			]);
			
			protected function calc_clickHandler(event:MouseEvent):void
			{
				var m:int=this.mark.selectedIndex;
				var num1:Number=Number(this.firstnum.text);
				var num2:Number=Number(this.secondnum.text);
				if(m==-1){
					Alert.show("请选择运算符","信息");
					return;
				}
				var res:Number;
				switch(m){
					case 0:
						res=num1+num2;
						break;
					case 1:
						res=num1-num2;
						break;
					case 2:
						res=num1*num2;
						break;
					case 3:
						res=num1/num2;
						break;
				}
				this.result.text=res.toFixed(2);
			}
			
			
			protected function clear_clickHandler(event:MouseEvent):void
			{
				this.firstnum.text=null;
				this.secondnum.text=null;
				this.result.text=null;
				this.mark.selectedIndex=-1;
			}
			
		]]>
	</fx:Script>
	<s:Label text="第一个数:" x="171" y="87"/>
	<s:TextInput id="firstnum" x="261" y="82"/>
	<s:Label text="第二个数:" x="171" y="122"/>
	<s:TextInput id="secondnum" x="261" y="122"/>
	<s:Label text=" 结 果:" x="189" y="205"/>
	<s:TextInput id="result" x="261" y="195"/>
	<s:Button label="计算"  x="261" y="244" click="calc_clickHandler(event)"/>
	<s:Button x="382" y="244" label="清空" click="clear_clickHandler(event)"/>
	<tudou:closeWindowBtn />
	<s:Label x="183" y="153" text="运算符:"/>
	<s:DropDownList x="261" y="153" prompt="--请选择运算符--" width="128" id="mark" dataProvider="{mydp}" labelField="text" selectedIndex="-1">
	</s:DropDownList>
</s:Application>