<?xml version="1.0"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml">
 
    <mx:Script>
        <![CDATA[
            import mx.controls.Alert;
            import mx.events.ValidationResultEvent;
 
            private function validateForm():void {
                var result:ValidationResultEvent = numVal.validate();
 
                switch (result.type) {
                    case ValidationResultEvent.INVALID:
                        Alert.show(result.message, "Error!");
                        break;
                    case ValidationResultEvent.VALID:
                        Alert.show("Thanks!");
                        break;
                }
            }
        ]]>
    </mx:Script>
 
    <mx:NumberValidator id="numVal" 
            source="{lst}" 
            property="selectedIndex"
            minValue="0"
            lowerThanMinError="Please select an item from the list." />
 
    <mx:Form defaultButton="{btn}">
        <mx:FormItem label="Products:">
            <mx:List id="lst" 
                    allowMultipleSelection="true"
                    width="100">
                <mx:dataProvider>
                    <mx:ArrayCollection source="[one,two,three,four,five,six,seven,eight,nine,ten]" />
                </mx:dataProvider>
            </mx:List>
        </mx:FormItem>
        <mx:FormItem>
            <mx:Button id="btn"
                    label="Submit"
                    click="validateForm();" />
        </mx:FormItem>
    </mx:Form>
 
</mx:Application>

textInputBox = new MyTextInput;
 
textInputBox.restrict = "0-9.";
textInputBox.maxChars = 24;
amountValidator = new NumberValidator();
amountValidator.source = textInputBox;
amountValidator.property = "text";
amountValidator.allowNegative = false;
amountValidator.domain = "real";
amountValidator.precision = 4;
amountValidator.required = false;
amountValidator.maxValue = 999999999999.9999;
amountValidator.trigger = textInputBox;
amountValidator.triggerEvent = Event.CHANGE;
amountValidator.addEventListener(ValidationResultEvent.VALID, amountValid);
amountValidator.addEventListener(ValidationResultEvent.INVALID, amountInvalid);
 
private function amountValid(event:ValidationResultEvent):void
{
    valid = true;
    fieldsValidated = true;
}
 
private function amountInvalid(event:ValidationResultEvent):void
{
    valid = false;
    fieldsValidated = true;
}