Help in datagrid FLEX

I need to drag the column to the first grid and capture the name of the column in order to determine whether the column is visible or not. See sample:

http://www.techall.com.br/GRID/Index.html

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" width="100%" height="100%" backgroundGradientAlphas="[1.0, 1.0]" backgroundGradientColors="[#FFFFFF, #FFFFFF]">
<mx:Script>
	<![CDATA[
		
		
		
		
		
	]]>
</mx:Script>
<mx:Style>
	Application {
        backgroundImage:"Imagem/fundo2.jpg";
    }
</mx:Style>
<mx:XMLList id="employees">
        <employee>
            <name>Christina Coenraets</name>
            <phone>555-219-2270</phone>
            <email>ccoenraets@fictitious.com</email>
            <active>true</active>
            <image>images/arrow_icon_sm.png</image>
        </employee>
        <employee>
            <name>Joanne Wall</name>
            <phone>555-219-2012</phone>
            <email>jwall@fictitious.com</email>
            <active>true</active>
        </employee>
        <employee>
            <name>Maurice Smith</name>
            <phone>555-219-2012</phone>
            <email>maurice@fictitious.com</email>
            <active>false</active>
        </employee>
        <employee>
            <name>Mary Jones</name>
            <phone>555-219-2000</phone>
            <email>mjones@fictitious.com</email>
            <active>true</active>
        </employee>
    </mx:XMLList>
	<mx:Canvas y="77" width="1000" height="692" backgroundColor="#FFFFFF" alpha="1.0" borderStyle="solid" cornerRadius="10" horizontalCenter="8" borderThickness="3" backgroundAlpha="0.36">
		<mx:ViewStack x="0" y="0" id="viewstack1" width="994" height="686">
			<mx:Canvas label="View 1" width="100%" height="100%">
				<mx:Canvas x="10" y="10" width="165" height="666" backgroundColor="#FFFFFF" borderStyle="solid" cornerRadius="10" backgroundAlpha="0.19">
					<mx:Canvas x="0" y="0" width="163" height="664" horizontalScrollPolicy="off">
						<mx:Canvas x="0" y="0" width="163" height="914">
							<mx:DataGrid x="5" y="10" width="138" height="255" dataProvider="[]" color="#000000" fontWeight="bold"  dragEnabled="true" dropEnabled="true" dragMoveEnabled="true">
								<mx:columns>
									<mx:DataGridColumn headerText="AGRUPAMENTO" dataField="name"/>
								</mx:columns>
							</mx:DataGrid>
							<mx:DataGrid x="6" y="285" width="137" height="255" color="#000000" fontWeight="bold">
								<mx:columns>
									<mx:DataGridColumn headerText="EXIBIR COLUNAS" dataField="col1"/>
								</mx:columns>
							</mx:DataGrid>
							<mx:DataGrid x="4" y="595" width="138" height="89" color="#000000" fontWeight="bold">
								<mx:columns>
									<mx:DataGridColumn headerText="FILTRAR COLUNA" dataField="col1"/>
								</mx:columns>
							</mx:DataGrid>
							<mx:HRule x="2" y="272" height="5" width="160"/>
							<mx:HRule x="2" y="582" height="5" width="160"/>
							<mx:DataGrid x="10" y="755" width="133" height="149" color="#000000" fontWeight="bold">
								<mx:columns>
									<mx:DataGridColumn headerText="CÁLCULAR COLUNA" dataField="col1"/>
								</mx:columns>
							</mx:DataGrid>
							<mx:HRule x="2" y="742" height="5" width="160"/>
							<mx:HRule x="2" y="692" height="5" width="160"/>
							<mx:CheckBox x="26" y="548" label="EXIBIR TODAS" fontWeight="bold" color="#000000"/>
							<mx:CheckBox x="26" y="708" label="QUANTIDADE" fontWeight="bold" color="#000000"/>
						</mx:Canvas>
					</mx:Canvas>
				</mx:Canvas>
				<mx:Canvas x="183" y="10" width="801" verticalScrollPolicy="off" horizontalScrollPolicy="off" height="44" backgroundColor="#FFFFFF" borderStyle="solid" cornerRadius="10" backgroundAlpha="0.19">
					<mx:Label x="11" y="12" text="EXPORTAR EM:" fontStyle="normal" fontWeight="bold" color="#000000"/>
					<mx:Image x="124" y="3" source="Imagem/EXCEL.png"/>
					<mx:Image x="168" y="3" source="Imagem/WORD.png"/>
					<mx:Image x="211" y="4" source="Imagem/IE.png"/>
					<mx:Image x="253" y="4" source="Imagem/PDF.png"/>
					<mx:Image x="312" y="3" source="Imagem/GRAFICOS.png" buttonMode="true" click="{GRAFICOS.visible = true}"/>
					<mx:VRule x="291" y="6" width="6" height="32"/>
					<mx:Label x="441" y="14" text="FILTRAR" fontStyle="normal" fontWeight="bold" color="#000000"/>
					<mx:TextInput x="504" y="11" width="285"/>
				</mx:Canvas>
				<mx:Canvas x="183" y="62" width="801" height="563">
					<mx:DataGrid x="0" y="0" width="1500" dataProvider="{employees}" height="544" id="GRID" allowMultipleSelection="true" dragEnabled="true" dragMoveEnabled="true">
						<mx:columns>
							<mx:DataGridColumn headerText="Column 1" dataField="name" id="a"/>
							<mx:DataGridColumn headerText="Column 2" dataField="phone"/>
							<mx:DataGridColumn headerText="Column 3" dataField="email"/>
							<mx:DataGridColumn headerText="Column 1" dataField="active"/>
							<mx:DataGridColumn headerText="Column 2" dataField="col2"/>
							<mx:DataGridColumn headerText="Column 3" dataField="col3"/>
							<mx:DataGridColumn headerText="Column 1" dataField="col1"/>
							<mx:DataGridColumn headerText="Column 2" dataField="col2"/>
							<mx:DataGridColumn headerText="Column 3" dataField="col3"/>
						</mx:columns>
					</mx:DataGrid>
					<mx:Canvas x="173" y="3" width="269" visible="false" height="60" backgroundColor="#EBEBEE" borderStyle="solid" cornerRadius="10" id="GRAFICOS">
						<mx:LinkButton x="10" y="22" label="PIZZA" color="#000000" themeColor="#E46C01"/>
						<mx:LinkButton x="75" y="22" label="COLUNAS" color="#000000" themeColor="#E46C01"/>
						<mx:LinkButton x="157" y="22" label="BARRAS" color="#000000" themeColor="#E46C01"/>
						<mx:Image x="245" y="2" source="Imagem/1267291268_x.png" buttonMode="true" click="{GRAFICOS.visible = false}"/>
					</mx:Canvas>
				</mx:Canvas>
			</mx:Canvas>
			<mx:Canvas label="A" width="100%" height="100%">
			</mx:Canvas>
		</mx:ViewStack>
	</mx:Canvas>
	<mx:ControlBar x="0" y="0" width="100%" height="55">
		<mx:Image source="Imagem/logo_peq.png"/>
	</mx:ControlBar>
</mx:Application>

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