< asp : GridView ID ="gridView" AllowPaging ="true" AllowSorting ="true "

         OnPageIndexChanging ="gridView_PageIndexChanging" OnSorting ="gridView_Sorting"

         runat ="server" />

 

    private string GridViewSortDirection

    {

        get { return ViewState[ "SortDirection" ] as string ?? "ASC" ; }

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

    }

 

    private string GridViewSortExpression

    {

        get { return ViewState[ "SortExpression" ] as string ?? string .Empty; }

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

    }

 

    private string GetSortDirection()

    {

        switch (GridViewSortDirection)

        {

            case "ASC" :

                GridViewSortDirection = "DESC" ;

                break ;

 

            case "DESC" :

                GridViewSortDirection = "ASC" ;

                break ;

        }

 

        return GridViewSortDirection;

    }

 

    protected void gridView_PageIndexChanging( object sender, GridViewPageEventArgs e)

    {

        gridView.DataSource = SortDataTable(gridView.DataSource as DataTable , true );

        gridView.PageIndex = e.NewPageIndex;

        gridView.DataBind();

    }

 

    protected DataView SortDataTable( DataTable dataTable, bool isPageIndexChanging)

    {

        if (dataTable != null )

        {

            DataView dataView = new DataView (dataTable);

            if (GridViewSortExpression != string .Empty)

            {

                if (isPageIndexChanging)

                {

                    dataView.Sort = string .Format( "{0} {1}" , GridViewSortExpression, GridViewSortDirection);

                }

                else

                {

                    dataView.Sort = string .Format( "{0} {1}" , GridViewSortExpression, GetSortDirection());

                }

            }

            return dataView;

        }

        else

        {

            return new DataView ();

        }

    }

 

    protected void gridView_Sorting( object sender, GridViewSortEventArgs e)

    {

        GridViewSortExpression = e.SortExpression;

        int pageIndex = gridView.PageIndex;

        gridView.DataSource = SortDataTable(gridView.DataSource as DataTable , false );

        gridView.DataBind();

        gridView.PageIndex = pageIndex;

    }