Gridview in disconnected mode

aspx.cs

using BusinessLayer;
using PropertyLayer;
using System.Data.SqlClient;

namespace Gv_Disconnected_NTier_
{
    public partial class Gv_DisconnectedMode : System.Web.UI.Page
    {
        DataTable d1 = new DataTable();

        protected void Page_Load(object sender, EventArgs e)
        {
            if (Page.IsPostBack == false)
            {
                GvBusinessLayer objBusinessLayer = new GvBusinessLayer();
                d1 = objBusinessLayer.GetStudentDetails("student_records");
                ViewState["d1"] = d1;
                bind();
            }
            else
            {
                 d1 = (DataTable)ViewState["d1"];
            }
        }