flex 正则表达式验证

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
         creationComplete="init()"
        backgroundColor="white">
 
    <mx:Script>
        <![CDATA[
            private const postalcode_regex:RegExp = /^[A-Z][0-9][A-Z] [0-9][A-Z][0-9]$/i;
 
            private function validatePostalCode(evt:Event):void {
           
                if (postalcode_regex.test(ti1text)) {
                    ti1.errorString = null;
                    ti1.setStyle("borderColor", "#081fc5");//通过变蓝色
                   
                } else {
                    ti1.errorString = postalCode_errorString;
                    ti1.setStyle("borderColor", "#ff0000");//没有通过变红色
                }
            }
            private function init():void
            {
            ti1.setStyle("borderColor", "#000000");//初始化的时候 黑色
            }
        ]]>
    </mx:Script>
 
    <mx:String id="ti1text">{ti1.text}</mx:String>
    <mx:String id="postalCode_errorString">
        <![CDATA[Please enter a valid postal code in "L9L 9L9" format.]]>
    </mx:String> 
    <mx:Form>
        <mx:FormItem label="Postal Code:" required="true">
            <mx:TextInput id="ti1"
                    maxChars="7"
                    restrict="A-Z 0-9"
                    change="validatePostalCode(event)" />
        </mx:FormItem>
    </mx:Form>
                    <mx:TextInput id="textInput" />
   
 
</mx:Application>