GridView正反排序(C#)

实现正反排序:
前台: 
  <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" 
                 AllowSorting="True" OnSorting="Sorting">
                <Columns>
                    <asp:BoundField DataField="name" HeaderText="name" SortExpression="name" />
                    <asp:BoundField DataField="age" HeaderText="age" SortExpression="age" />
                    <asp:BoundField DataField="sex" HeaderText="sex" />
                </Columns>
            </asp:GridView>
后台:
public partial class asp_Test_Default38 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            ViewState["sortColumn"] = "name";
            ViewState["sortModel"] = "ASC";
            Bind();
        }
    }
    public void Bind()
    {
        DB db = new DB();
        string sql = "select * from student";
        DataTable dt = db.GetDataTabel(sql);
        DataView dv = dt.DefaultView;//通过DataView的Sort属性来排序
        dv.Sort =(string)ViewState["sortColumn"]+" "+(string)ViewState["sortModel"];
        this.GridView1.DataSource = dv;