GridView點擊排序時帶小圖片

using System;
using System.Data;
using System.Configuration;
using System.Collections;
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.Data.OleDb;
public partial class Sorting : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            this.BindGridView();
        }
    }
    /// <summary>
    /// 綁定gridview
    /// </summary>
    public void BindGridView()
    {

        string sql = "select * from tb_test";
        //獲取gridview排序的數據列及其方向
        string sortExpression = this.GridView1.Attributes["SortExpression"];
        string sortDirection = this.GridView1.Attributes["SortDirection"];
        //調用方法
        DataTable dt = new DataTable();
        dt = OracleHelper.getDB(sql);
        if ((!string.IsNullOrEmpty(sortExpression)) && (!string.IsNullOrEmpty(sortDirection)))
        {
            dt.DefaultView.Sort = string.Format("{0} {1}", sortExpression, sortDirection);
        }
        //GridView綁定并顯示數據
        this.GridView1.DataSource = dt;
        this.GridView1.DataBind();


    }

    /// <summary>
    /// 排序
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="e"></param>
    protected void GridView1_Sorting(object sender, GridViewSortEventArgs e)
    {
        //從事件參數中獲取排序的數據列
        string sortExpression = e.SortExpression.ToString();
        //假定排序方向為‘順序’
        string sortDirection = "ASC";
        //'ASC' 與從時間參數獲取的排序方向相比較，進行gridview排序方向的修改
        if (sortExpression == this.GridView1.Attributes["SortExpression"])
        {
            //獲取下一次排序狀態
            sortDirection = (this.GridView1.Attributes["SortDirection"].ToString() == sortDirection ? "DESC" : "ASC");
        }
        // 重新设定GridView排序数据列及排序方向
        this.GridView1.Attributes["SortExpression"] = sortExpression;
        this.GridView1.Attributes["SortDirection"] = sortDirection;
        this.BindGridView();

        GridViewRow headerRow = GridView1.HeaderRow;
        Image sortImage = new Image();
        if (sortDirection == "ASC")
        {
            sortImage.ImageUrl = "images/hmenu-asc.gif";
            sortImage.Style.Add("vertical-align", "bottom");
        }
        else
        {
            sortImage.ImageUrl = "images/hmenu-desc.gif";
            sortImage.Style.Add("vertical-align", "bottom");
        }
        int num = 0;
        foreach (DataControlField field in GridView1.Columns)
        {
            if (field.SortExpression == sortExpression.ToString().Trim())
            {
                num = GridView1.Columns.IndexOf(field);
            }
        }
        headerRow.Cells[num].Controls.Add(sortImage);
      
    }
}

 

   public static DataTable getDB(string sql)
    {
        DataTable dt = new DataTable();
        using (OleDbConnection conn = new OleDbConnection(ConnString))
        {
            OleDbDataAdapter comm = new OleDbDataAdapter(sql, conn);
            DataSet ds = new DataSet();
            try
            {
                conn.Open();
                ds.Clear();
                comm.Fill(ds);
                dt = ds.Tables[0];

            }
            catch
            {
                conn.Close();
            }
            finally
            {
                conn.Close();
            }
            return dt;
        }

    }