<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" BackColor="White" BorderColor="#CC9966" BorderStyle="Solid" BorderWidth="1px" CellPadding="4"  AllowSorting="True"  OnSorting="GridView1_Sorting" >

        <Columns>

            <asp:TemplateField HeaderText="Emp_ID" SortExpression="Emp_ID">

                <ItemTemplate>

                    <%#Eval("Emp_ID") %>

                </ItemTemplate>

                <ControlStyle Width="100px"></ControlStyle>

                <HeaderStyle Width="100px" />

                <ItemStyle HorizontalAlign="Center" />

            </asp:TemplateField>


            <asp:TemplateField HeaderText="Emp_Name" SortExpression="Emp_Name">

                <ItemTemplate>

                    <%#Eval("Emp_Name") %>

                </ItemTemplate>


                <ControlStyle Width="300px"></ControlStyle>

                <HeaderStyle Width="200px" />

            </asp:TemplateField>

            <asp:TemplateField HeaderText="Emp_Sal"  SortExpression="Emp_Sal">

                <ItemTemplate>

                    <%#Eval("Emp_Sal") %>

                </ItemTemplate>


                <ControlStyle Width="200px"></ControlStyle>

                <HeaderStyle Width="200px" />

            </asp:TemplateField>

        </Columns>

        <FooterStyle BackColor="#FFFFCC" ForeColor="#330099" />

        <HeaderStyle BackColor="#990000" Font-Bold="True" ForeColor="#FFFFCC" />

        <PagerStyle BackColor="#FFFFCC" ForeColor="#330099" HorizontalAlign="Center" />

        <RowStyle BackColor="White" ForeColor="#330099" />

        <SelectedRowStyle BackColor="#FFCC66" Font-Bold="True" ForeColor="#663399" />

        <SortedAscendingCellStyle BackColor="#FEFCEB" />

        <SortedAscendingHeaderStyle BackColor="#AF0101" />

        <SortedDescendingCellStyle BackColor="#F6F0C0" />

        <SortedDescendingHeaderStyle BackColor="#7E0000" />

    </asp:GridView>

using System;
using System.Collections.Generic;
using System.Configuration;
using System.Data;
using System.Data.SqlClient;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
namespace Forumasp
{
    public partial class GridviewSorting : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)

	{

           GridView1.DataSource = GetRecord(); //set DataSource GridView
            GridView1.DataBind(); //binding GridView
       }

        protected void GridView1_PageIndexChanging(object sender, GridViewPageEventArgs e)

        {
            GridView1.PageIndex = e.NewPageIndex;
            GridView1.DataSource = GetRecord();
                GridView1.DataBind();       
        }

        public DataTable GetRecord()

        {
            DataTable dt = new DataTable();

            string constr = ConfigurationManager.ConnectionStrings["forumConnectionString"].ToString(); // connection string

            SqlConnection con = new SqlConnection(constr);

            con.Open();
            SqlCommand com = new SqlCommand("select *from Employee", con); // table name 

            SqlDataAdapter da = new SqlDataAdapter(com);

            DataSet ds = new DataSet();

            da.Fill(ds);   
          dt=  ds.Tables[0];
          return dt;
 }

        public SortDirection direction

        {
            get

            {
                if (ViewState["directionState"] == null)

                {
                    ViewState["directionState"] = SortDirection.Ascending;

                }
                return (SortDirection)ViewState["directionState"];

            }
            set

            {
                ViewState["directionState"] = value;

            }
        }

        protected void GridView1_Sorting(object sender, GridViewSortEventArgs e)

        {
            string sortingDirection = string.Empty;

            if (direction == SortDirection.Ascending)

            {
                direction = SortDirection.Descending;

                sortingDirection = "Desc";


            }
            else

            {
                direction = SortDirection.Ascending;

                sortingDirection = "Asc";


            }
            DataView sortedView = new DataView(GetRecord());

            sortedView.Sort = e.SortExpression + " " + sortingDirection;

            Session["SortedView"] = sortedView;

            GridView1.DataSource = sortedView;
            GridView1.DataBind();  
        }  
 
    }
}