求助，程序问题？

using System;
using System.Data;
using System.Configuration;
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.SqlClient;

public partial class _list : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {

        SqlConnection con = new SqlConnection(@"DataSource =.\SQLEXPRESS; database=Select; uid=sa;pwd=;");
        con.Open();
        SqlCommand cmd=new SqlCommand ("select * from personLike",con );
        SqlDataReader sdr=cmd .ExecuteReader ();
        this.CheckBoxList1.DataSource =sdr ;
        this.CheckBoxList1.DataTextField = "likeContent";
        this.CheckBoxList1.DataValueField = "id";
        this.CheckBoxList1.DataBind();
        
    }

    protected void Button1_Click(object sender, EventArgs e)
    {

        for (int i = 0; i < this.CheckBoxList1.Items[i].Count - 1; i++)
        {
            if (this.CheckBoxList1.Items[i].Selected)
            {
                Response.Write(this.CheckBoxList1.Items[i].Text + "<br>");
            }

        }
    }
}

这句for (int i = 0; i < this.CheckBoxList1.Items[i].Count - 1; i++)
出现 CS0117: “System.Web.UI.WebControls.ListItem”并不包含“Count”的定义，是不是还科缺少什么命名空间？
请各位帮忙看一下，谢谢！