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(0, 0, 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) > 0 || 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 = 0; i < sortColumns.Length; i++)
        {

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

            else if (descSortExpression.Equals(sortColumns[i]))
            {
                Array.Clear(sortColumns, i, 1);
            }
        }

        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 = -1;
        for (int i = 0; i < sortColumns.Length; i++)
        {
            if (sortColumns[i].StartsWith(sortColumn))
            {
                sortOrderNo = i + 1;
                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 = 0; i < dgItem.Cells.Count; i++)
        {
            if (dgItem.Cells[i].Controls.Count > 0 && dgItem.Cells[i].Controls[0] is LinkButton)
            {
                string sortOrder;
                int sortOrderNo;
                string column = ((LinkButton)dgItem.Cells[i].Controls[0]).CommandArgument;
                SearchSortExpression(sortColumns, column, out sortOrder, out sortOrderNo);
                if (sortOrderNo > 0)
                {
                    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
}