ListBox中怎么实现多选并显示数据

<%@ Page Language="C#" AutoEventWireup="true" Debug="true"%>  <%@import namespace="System.Data"%>  <%@import namespace="System.Data.SqlClient"%>  <FORM RUNAT=< SPAN>"server">  "ckbEmployees" runat="server" RepeatLayout="table" RepeatDirection="vertical" RepeatColumns="3" CellPadding="9" CellSpacing="18" TextAlign="right" OnSelectedIndexChanged="subListChange" AutoPostBack="true" />   "dgEmployee" runat="server" />  <SCRIPT LANGUAGE=< SPAN>"c#" runat="server">  private void Page_load(object sender,System.EventArgs e)  {  if(!IsPostBack)  {     string strConnection ="server=.;uid=sa;pwd=sunix!;database=northwind";     string strSQLforCheckBoxes = "select LastName ,EmployeeID from employees order by lastname";     SqlConnection objConnection = new SqlConnection(strConnection);     SqlCommand objCommand = new SqlCommand(strSQLforCheckBoxes,objConnection);     objConnection.Open();     ckbEmployees.DataSource = objCommand.ExecuteReader();     ckbEmployees.DataTextField = "LastName";     ckbEmployees.DataValueField = "EmployeeID";     ckbEmployees.DataBind();     objConnection.Close();  }  }  private void subListChange(object s,System.EventArgs e)  {  Response.Write("subListchange triggered");  string strWhereClause="";  foreach (ListItem liThisOne in ckbEmployees.Items)  {     if(liThisOne.Selected)     {      strWhereClause += "EmployeeID = " + liThisOne.Value + " OR ";     }  }  Response.Write("strWhereClause="+strWhereClause+"");  if(strWhereClause.Length>0)  {     dgEmployee.Visible = true;     string str = strWhereClause.Substring(0,strWhereClause.Length - 3);     strWhereClause = " where " + str;     string strConnection = "server=.;uid=sa;pwd=sunix!;database=northwind";     string strSQLforGrid = "select TitleOfCourtesy,firstName,lastName,country,region,city,notes from employees " + strWhereClause;       //Response.Write(strSQLforGrid); sql语句之间的空格,否则出错     SqlConnection objConnection = new SqlConnection(strConnection);     SqlCommand objCommand = new SqlCommand(strSQLforGrid,objConnection);     Response.Write("strSQLforGrid="+strSQLforGrid+"");     objConnection.Open();     dgEmployee.DataSource = objCommand.ExecuteReader();     dgEmployee.DataBind();     objConnection.Close();  }  else {     dgEmployee.Visible = false;  }  }