Flex DataGrid取其中的某一个值

<?xml version="1.0"?>
<!-- DataGrid control example. -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml">

    <mx:XMLList id="employees">
        <employee>
            <name>Christina Coenraets</name>
            <phone>555-219-2270</phone>
            <email>[e-mail]</email>
            <active>true</active>
        </employee>
        <employee>
            <name>Joanne Wall</name>
            <phone>555-219-2012</phone>
            <email>[e-mail]</email>
            <active>true</active>
        </employee>
        <employee>
            <name>Maurice Smith</name>
            <phone>555-219-2012</phone>
            <email>[e-mail]</email>
            <active>false</active>
        </employee>
        <employee>
            <name>Mary Jones</name>
            <phone>555-219-2000</phone>
            <email>[e-mail]</email>
            <active>true</active>
        </employee>
    </mx:XMLList>
	<mx:Script>
		<![CDATA[
			import mx.collections.ArrayCollection;
			import mx.controls.Alert;
			private function clickHandle():void
			{
				var h:String = dg.dataProvider[0].name;
				trace(h);
				var o:Object = dg.dataProvider;
				trace((new ArrayCollection(dg.dataProvider.toArray())).length);
				
				Alert.show(dg.selectedItem.name);
			}
		]]>
	</mx:Script>
    <mx:Panel title="DataGrid Control Example" height="100%" width="100%" 
        paddingTop="10" paddingLeft="10" paddingRight="10">

        <mx:Label width="100%" color="blue"
            text="Select a row in the DataGrid control."/>

        <mx:DataGrid id="dg" width="100%" height="100%" rowCount="5" dataProvider="{employees}">
            <mx:columns>
                <mx:DataGridColumn dataField="name" headerText="Name"/>
                <mx:DataGridColumn dataField="phone" headerText="Phone"/>
                <mx:DataGridColumn dataField="email" headerText="Email"/>
            </mx:columns>
        </mx:DataGrid>

        <mx:Form width="100%" height="100%">
            <mx:FormItem label="Name">
                <mx:Label text="{dg.selectedItem.name}"/>
            </mx:FormItem>
            <mx:FormItem label="Email">
                <mx:Label text="{dg.selectedItem.email}"/>
            </mx:FormItem>
            <mx:FormItem label="Phone">
                <mx:Label text="{dg.selectedItem.phone}"/>
            </mx:FormItem>
        </mx:Form>
        <mx:Button click="clickHandle()"/>
    </mx:Panel>
</mx:Application>