Gridview Sorting and Paging in asp.net C#

Design:

<asp:GridView ID="gdvRecords" runat="server" CellPadding="4" ForeColor="#333333" GridLines="None" AllowPaging="True" PageSize="5" OnPageIndexChanging="gdvRecords_PageIndexChanging" AllowSorting="True" OnSorting="gdvRecords_Sorting">  </asp:GridView>

Paging:

     protected void gdvRecords_PageIndexChanging(object sender, GridViewPageEventArgs e)

     {

            GridView grdsample = (GridView)sender; //Get Current Gridview Object

            grdsample.PageIndex = e.NewPageIndex; //Set Page Index

            SqlConnection sqlcon = new SqlConnection(onnectionString);

            SqlCommand sqlcmdinsert = new SqlCommand("select * from Table",sqlcon);

            SqlDataAdapter sqlda = new SqlDataAdapter(sqlcmdinsert);         

            sqlda.Fill(dsAllData);

            gdvRecords.DataSource = dsAllData.Tables[0];

            gdvRecords.DataBind();

     }

Sorting:

   private const string ASCENDING = " ASC";

   private const string DESCENDING = " DESC";

   public SortDirection GridViewSortDirection

   {

        get

        {

            if (ViewState["sortDirection"] == null)

                ViewState["sortDirection"] = SortDirection.Ascending;

                return (SortDirection)ViewState["sortDirection"];

          }

            set { ViewState["sortDirection"] = value; }

   }

        private void SortGridView(string sortExpression, string direction)

        {

            DataTable dt;

            if (chkAll.Checked == true)

            {

                bindAllData();

                dt = dsAllData.Tables[0];

            }

            else

            {

                bindSearchData();

                dt = dsSearch.Tables[0];

            }

            //  You can cache the DataTable for improving performance

          

            DataView dv = new DataView(dt);

            dv.Sort = sortExpression + direction;

            gdvRecords.DataSource = dv;

            gdvRecords.DataBind();

        }

        protected void gdvRecords_Sorting(object sender, GridViewSortEventArgs e)

        {

            string sortExpression = e.SortExpression;

            if (GridViewSortDirection == SortDirection.Ascending)

            {

                GridViewSortDirection = SortDirection.Descending;

                SortGridView(sortExpression, DESCENDING);

            }

            else

            {

                GridViewSortDirection = SortDirection.Ascending;

                SortGridView(sortExpression, ASCENDING);

            }

        }