GridView:Sorting & Paging Using Generics And Nullable Datatype Function Of C# GetValueOrDefault()

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Collections.Generic;

namespace SortingAndPaging
{
    public partial class CountryView : System.Web.UI.Page
    {
        #region Page Load Event
        /// <summary>
        /// On Page Load:Sort Country Ascending Order/Sort Column: CountryID
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void Page_Load(object sender, EventArgs e)
        {
            try
            {
                if (IsPostBack == false)
                {
                    SortColumn = Country.CountryComparer.CountryComparisonType.CountryID;
                    SortDirection = Utility.SortOrder.Asc;
                    LoadCountryList();
                }
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }
       
        /// <summary>
        /// OnRowCreated Event: Add 'Ascending' and 'Descending' image in Grid Header Control. 
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void gridCountry_RowCreated(object sender, GridViewRowEventArgs e)
        {
            try
            {
                if (e.Row.RowType == DataControlRowType.Header)
                {
                    foreach (TableCell tableCell in e.Row.Cells)
                    {
                        if (tableCell.HasControls())
                        {
                            LinkButton columnLinkButton = (LinkButton)tableCell.Controls[0];
                            if (columnLinkButton != null)
                            {
                                System.Web.UI.WebControls.Image img = new System.Web.UI.WebControls.Image();
                                img.ImageUrl = "~/Image/" + this.SortDirection.ToString() + ".gif";
                                if (SortColumn == (Country.CountryComparer.CountryComparisonType)Enum.Parse(typeof(Country.CountryComparer.CountryComparisonType), columnLinkButton.CommandArgument))
                                {
                                    tableCell.Controls.Add(new LiteralControl(" "));
                                    tableCell.Controls.Add(img);
                                }
                            }
                        }
                    }
                }
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }
        #endregion

        #region Grid Events
        /// <summary>
        /// OnPageIndexChanging Event : Load Country List based on Current Sort Order and Sort Column.
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void gridCountry_PageIndexChanging(object sender, GridViewPageEventArgs e)
        {
            try
            {
                gridCountry.PageIndex = e.NewPageIndex;
                PagingCountryList();
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }

        /// <summary>
        /// OnSorting Event: Load and Sort Country List based on Column and Order selected.
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void gridCountry_Sorting(object sender, GridViewSortEventArgs e)
        {
            try
            {
                SortCountryList((Country.CountryComparer.CountryComparisonType)Enum.Parse(typeof(Country.CountryComparer.CountryComparisonType), e.SortExpression));
            }
            catch(Exception ex )
            {
                throw ex;
            }
        }
        #endregion

        #region Private Method
        /// <summary>
        /// Bind Grid with Country List DataSource.
        /// </summary>
        /// <param name="list"></param>
        private void BindGrid<T>(T list)
        {
            gridCountry.DataSource = list;
            gridCountry.DataBind();
        }

        /// <summary>
        /// Called By Grid Page Event
        /// </summary>
        private void PagingCountryList()
        {
            SortCountryList(Country.CountryComparer.CountryComparisonType.NULL);
        }

        /// <summary>
        /// Called By PageLoad Event
        /// </summary>
        private void LoadCountryList()
        {
            SortCountryList(Country.CountryComparer.CountryComparisonType.NULL);
        }

        /// <summary>
        /// Called By Grid Sort Event
        /// </summary>
        /// <param name="sortExpression"></param>
        private void SortCountryList(Country.CountryComparer.CountryComparisonType sortExpression)
        {
            List<Country> countryList = (List<Country>)GetCountryList();
            Country.CountryComparer countryComparer = new Country.CountryComparer();
            if (Country.CountryComparer.CountryComparisonType.NULL != sortExpression)
            {
                if (sortExpression == SortColumn)
                {
                    if (SortDirection == Utility.SortOrder.Asc)
                    {
                        SortDirection = Utility.SortOrder.Desc;
                    }
                    else
                    {
                        SortDirection = Utility.SortOrder.Asc;
                    }
                }
                else
                {
                    SortDirection = Utility.SortOrder.Asc;
                }
                SortColumn = sortExpression;
            }
            countryComparer.WhichComparison = SortColumn;
            countryComparer.SortDirection = SortDirection;
            countryList.Sort(countryComparer);
            CountryDataSource = countryList;
        }

        /// <summary>
        /// Fetch Data from database and fill country collection list.
        /// </summary>
        /// <returns></returns>
        private IList<Country> GetCountryList()
        {
            IList<Country> countryList = new List<Country>();
            countryList.Add(new Country(1, "United States Of America", 100001));
            countryList.Add(new Country(2, "Africa", null));
            countryList.Add(new Country(3, "India", null));
            countryList.Add(new Country(4, "Singapore", 100004));
            countryList.Add(new Country(5, "Newzealand", 100005));
            countryList.Add(new Country(6, "United Kingdom", 100006));
            countryList.Add(new Country(7, "Australia", 100007));
            countryList.Add(new Country(8, "China", 100008));
            countryList.Add(new Country(9, "Malaysia", null));
            countryList.Add(new Country(10, "Germany", 100011));
            countryList.Add(new Country(11, "France", 100009));
            countryList.Add(new Country(12, "United States Of Soviet Russia", null));
            return countryList;
        }
        #endregion

        #region Private Property
        /// <summary>
        /// Property CountryDataSource
        /// </summary>
        private IList<Country> CountryDataSource
        {
            get { return (List<Country>)gridCountry.DataSource; }
            set { BindGrid(value);}
        }
        /// <summary>
        /// Property SortColumn
        /// </summary>
        private Country.CountryComparer.CountryComparisonType SortColumn
        {
            get { return (Country.CountryComparer.CountryComparisonType)ViewState["SORT_EXP"]; }
            set { ViewState["SORT_EXP"] = value; }
        }
        /// <summary>
        /// Property SortDirection
        /// </summary>        
        private Utility.SortOrder SortDirection
        {
            get { return (Utility.SortOrder)ViewState["SORT_ORDER"]; }
            set { ViewState["SORT_ORDER"] = value; }
        }
        #endregion
    }
}