GridView多列排序

 public class WebGridView:GridView
 {
     属性#region 属性
     /**//// <summary>
     /// 是否启用或者禁止多列排序
     /// </summary>
     [
     Description("是否启用多列排序功能"),
     Category("排序"),
     DefaultValue("false"),
     ]
     public bool AllowMultiColumnSorting
     {
         get
         {
             object o = ViewState["EnableMultiColumnSorting"];
             return (o != null ? (bool)o : false);
         }
         set
         {
             AllowSorting = true;
             ViewState["EnableMultiColumnSorting"] = value;
         }
     }
     /**//// <summary>
     /// 升序时显示图标
     /// </summary>
     [
     Description("升序时显示图标"),
     Category("排序"),
     Editor("System.Web.UI.Design.UrlEditor", typeof(System.Drawing.Design.UITypeEditor)),
     DefaultValue(""),

     ]
     public string SortAscImageUrl
     {
         get
         {
             object o = ViewState["SortImageAsc"];
             return (o != null ? o.ToString() : "");
         }
         set
         {
             ViewState["SortImageAsc"] = value;
         }
     }
     /**//// <summary>
     /// 降序时显示图标
     /// </summary>
     [
     Description("降序时显示图标"),
     Category("排序"),
     Editor("System.Web.UI.Design.UrlEditor", typeof(System.Drawing.Design.UITypeEditor)),
     DefaultValue(""),
     ]
     public string SortDescImageUrl
     {
         get
         {
             object o = ViewState["SortImageDesc"];
             return (o != null ? o.ToString() : "");
         }
         set
         {
             ViewState["SortImageDesc"] = value;
         }
     }
     #endregion
     重写方法#region 重写方法
     protected override void OnSorting(GridViewSortEventArgs e)
     {
         if (AllowMultiColumnSorting)
         {
             e.SortExpression = GetSortExpression(e);
         }

         base.OnSorting(e);
     }
     protected override void OnRowCreated(GridViewRowEventArgs e)
     {
         if (e.Row.RowType == DataControlRowType.Header)
         {
             if (SortExpression != String.Empty)
             {
                 DisplaySortOrderImages(SortExpression, e.Row);
                 this.CreateRow(, , DataControlRowType.EmptyDataRow, DataControlRowState.Normal);
             }
         }
         base.OnRowCreated(e);
     }
     #endregion
     受保护的方法#region 受保护的方法
     /**//// <summary>
     ///  获取排序表达式
     /// </summary>
     protected string GetSortExpression(GridViewSortEventArgs e)
     {
         string[] sortColumns = null;
         string sortAttribute = SortExpression;

         if (sortAttribute != String.Empty)
         {
             sortColumns = sortAttribute.Split(",".ToCharArray());
         }
         if (sortAttribute.IndexOf(e.SortExpression) >  || sortAttribute.StartsWith(e.SortExpression))
         {
             sortAttribute = ModifySortExpression(sortColumns, e.SortExpression);
         }
         else
         {
             sortAttribute += String.Concat(",", e.SortExpression, " ASC ");
         }
         return sortAttribute.TrimStart(",".ToCharArray()).TrimEnd(",".ToCharArray());

     }
     /**//// <summary>
     ///  修改排序顺序
     /// </summary>
     protected string ModifySortExpression(string[] sortColumns, string sortExpression)
     {
         string ascSortExpression = String.Concat(sortExpression, " ASC ");
         string descSortExpression = String.Concat(sortExpression, " DESC ");

         for (int i = ; i < sortColumns.Length; i++)
         {

             if (ascSortExpression.Equals(sortColumns[i]))
             {
                 sortColumns[i] = descSortExpression;
             }

             else if (descSortExpression.Equals(sortColumns[i]))
             {
                 Array.Clear(sortColumns, i, );
             }
         }

         return String.Join(",", sortColumns).Replace(",,", ",").TrimStart(",".ToCharArray());

     }
     /**//// <summary>
     ///  获取当前的表达式对所选列进行排序
     /// </summary>
     protected void SearchSortExpression(string[] sortColumns, string sortColumn, out string sortOrder, out int sortOrderNo)
     {
         sortOrder = "";
         sortOrderNo = -;
         for (int i = ; i < sortColumns.Length; i++)
         {
             if (sortColumns[i].StartsWith(sortColumn))
             {
                 sortOrderNo = i + ;
                 if (AllowMultiColumnSorting)
                 {
                     sortOrder = sortColumns[i].Substring(sortColumn.Length).Trim();
                 }
                 else
                 {
                     sortOrder = ((SortDirection == SortDirection.Ascending) ? "ASC" : "DESC");
                 }
             }
         }
     }
     /**//// <summary>
     ///  绘制升序降序的图片
     /// </summary>
     protected void DisplaySortOrderImages(string sortExpression, GridViewRow dgItem)
     {
         string[] sortColumns = sortExpression.Split(",".ToCharArray());

         for (int i = ; i < dgItem.Cells.Count; i++)
         {
             if (dgItem.Cells[i].Controls.Count >  && dgItem.Cells[i].Controls[] is LinkButton)
             {
                 string sortOrder;
                 int sortOrderNo;
                 string column = ((LinkButton)dgItem.Cells[i].Controls[]).CommandArgument;
                 SearchSortExpression(sortColumns, column, out sortOrder, out sortOrderNo);
                 if (sortOrderNo > )
                 {
                     string sortImgLoc = (sortOrder.Equals("ASC") ? SortAscImageUrl : SortDescImageUrl);

                     if (sortImgLoc != String.Empty)
                     {
                         Image imgSortDirection = new Image();
                         imgSortDirection.ImageUrl = sortImgLoc;
                         dgItem.Cells[i].Controls.Add(imgSortDirection);

                     }
                     else
                     {

                         if (AllowMultiColumnSorting)
                         {
                             Literal litSortSeq = new Literal();
                             litSortSeq.Text = sortOrderNo.ToString();
                             dgItem.Cells[i].Controls.Add(litSortSeq);

                         }
                     }
                 }
             }
         }

     }
     #endregion
 }