add rows to datagridview from datatable

<asp:gridview id="dgv" runat="server" xmlns:asp="#unknown">
<columns>
                            <asp:templatefield headertext="Name" itemstyle-width="150"> 
                                <itemtemplate>
                                   <%# DataBinder.Eval(Container.DataItem,"Name") %>
                               </itemtemplate>
                              
                            </asp:templatefield>
<pre lang="xml"><asp:templatefield headertext=""RollNo"" itemstyle-width=""150"">
                                <ItemTemplate>
                                   <%# DataBinder.Eval(Container.DataItem,'RollNo');
                              

                            </asp:TemplateField></asp:templatefield>

if(!IsPostBack)
{
BindGrid();
}


then after Page load create 

 protected void BindGrid()
{
SqlConnection con=new SqlConnection(ConfigurationManager.appSettings["dbConnection"].ToString());
SqlCommand cmd = new SqlCommand();
        cmd.CommandType = CommandType.Text;
        cmd.CommandText = "select * from tablename;



        cmd.Connection = con;
        con.Open();


        DataTable dt = new DataTable();
        SqlDataAdapter da = new SqlDataAdapter(cmd);

        da.Fill(dt);

        dgv.DataSource = dt;
        dgv.DataBind();

        cmd.Dispose();
        con.Close();

}