Auto number in gridview

<asp:GridView ID="GridView1" runat="server"
AutoGenerateColumns="False"
DataKeyNames="ProductID,ProductName"
DataSourceID="SqlDataSource1"
BackColor="White"
BorderColor="#3366CC"
BorderStyle="None"
BorderWidth="1px"
CellPadding="4"
onselectedindexchanged="GridView1_SelectedIndexChanged">
<FooterStyle BackColor="#99CCCC" ForeColor="#003399" />
<RowStyle BackColor="White" ForeColor="#003399" />
<Columns>
<asp:TemplateField>
<HeaderTemplate>NO</HeaderTemplate>
<ItemTemplate><%#Container.DataItemIndex+1%></ItemTemplate>
</asp:TemplateField>
<asp:BoundField DataField="ProductName" HeaderText="ProductName" SortExpression="ProductName" />
<asp:BoundField DataField="QuantityPerUnit" HeaderText="QuantityPerUnit" SortExpression="QuantityPerUnit" />
<asp:BoundField DataField="UnitPrice" HeaderText="UnitPrice" SortExpression="UnitPrice" />
<asp:BoundField DataField="UnitsInStock" HeaderText="UnitsInStock" SortExpression="UnitsInStock" />
<asp:BoundField DataField="UnitsOnOrder" HeaderText="UnitsOnOrder" SortExpression="UnitsOnOrder" />
</Columns>
<PagerStyle BackColor="#99CCCC" ForeColor="#003399" HorizontalAlign="Left" />
<SelectedRowStyle BackColor="#009999" Font-Bold="True" ForeColor="#CCFF99" />
<HeaderStyle BackColor="#003399" Font-Bold="True" ForeColor="#CCCCFF" />
<AlternatingRowStyle BackColor="#CCFFFF" />
</asp:GridView>

Reference