动态创建的textbox 更改里面的值后，获取不到控件

源码如下
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 AMDSchool.School.Common.Data;
using AMDSchool.School.BusinessFacade;namespace AMDSchool.WebUI.Task
{
    public partial class StudentDailyOnline : AMDSchool.WebCommon.DefaultPageBase
    {
        Guid userID;
        Guid cookieCompanyID;
        StudentDailyReportInputData data;
        protected void Page_Load(object sender, EventArgs e)
        {
            LabelNews.Text = DateTime.Now.ToShortDateString();
            userID = Bluematrix.Framework.Web.Intergrated.IntergratedSession.CurrentUser.Id;
            cookieCompanyID = AMDSchool.WebCommon.WebCommonConfigManager.CurrentCompanyID;
            if (!Page.IsPostBack)
            {
                BmTableSMS.SortColumnName = "Time";
                BmTableSMS.IsSortDesc = true;
                BmTableSMS.SortImageUrl = "/WebCommon/Images/BmTable/up.GIF";
                BmTableSMS.SortDescImageUrl = "/WebCommon/Images/BmTable/down.GIF";               
            }
        }        protected override void OnInit(EventArgs e)
        {
            BmTableSMS.HeadCellClicked += new Bluematrix.WebControls.BmTable.HeadCellClickedHandler(BmTableSMS_HeadCellClicked);
            base.OnInit(e);
        }        protected override void OnPreRender(EventArgs e)
        {
            ShowTable();
            base.OnPreRender(e);
        }        void BmTableSMS_HeadCellClicked(object sender, Bluematrix.WebControls.SortEventArgs e)
        {
            BmTableSMS.IsSortDesc = e.IsSortDesc;
            BmTableSMS.SortColumnName = e.FieldName;
        }        private void ShowTable()
        {
            BmTableSMS.Clear();
            BmTableSMS.BodyWidth = "100%";
            using (data = new StudentDailyReportSystem().GetDailyReportByUserID(cookieCompanyID, userID))
            {
                TableHeaderRow headRow = BmTableSMS.AddHeadRow();
                BmTableSMS.AddHeadCell(headRow, "编号", "20%").HorizontalAlign = HorizontalAlign.Center;
                BmTableSMS.AddHeadCell(headRow, "产品型号", "20%").HorizontalAlign = HorizontalAlign.Center;
                BmTableSMS.AddHeadCell(headRow, "销量", "20%").HorizontalAlign = HorizontalAlign.Center;
                BmTableSMS.AddHeadCell(headRow, "库存", "20%").HorizontalAlign = HorizontalAlign.Center;
                if (data == null || data.StudentDailyReportInput.Count == 0)
                    return;
                this.rowCount.Value = data.StudentDailyReportInput.Count.ToString();
                TableRow bodyRow;
                TableCell bodyCell;
                string cellText;
                for (int i = 0; i < data.StudentDailyReportInput.Count; i++)
                {
                    bodyRow = BmTableSMS.AddBodyRow();
                    bodyCell = BmTableSMS.AddCell(bodyRow, data.StudentDailyReportInput[i].Code, HorizontalAlign.Center);
                    bodyCell = BmTableSMS.AddCell(bodyRow, data.StudentDailyReportInput[i].Model, HorizontalAlign.Center);
                    if (data.StudentDailyReportInput[i].Stocks != null)
                    {
                        TextBox textBox = new TextBox();
                        textBox.Width = 30;
                        textBox.ID = "stocks" + i.ToString();
                        textBox.Text = data.StudentDailyReportInput[i].Stocks;
                        //cellText = string.Format("<input style=\"width:30px\" name=\"stocks" + i + "\" value= \"" + data.StudentDailyReportInput[i].Stocks + "\" />");
                        bodyCell = BmTableSMS.AddCell(bodyRow, "", HorizontalAlign.Center);
                        bodyCell.Controls.Add(textBox);
                    }
                    else
                    {
                        TextBox textBox = new TextBox();
                        textBox.Width = 30;
                        textBox.ID = "stocks" + i.ToString();
                        textBox.Text = "";
                        //cellText = string.Format("<input style=\"width:30px\" id=\"stocks" + i + "\" value= \"\" />");
                        bodyCell = BmTableSMS.AddCell(bodyRow, "", HorizontalAlign.Center);
                        bodyCell.Controls.Add(textBox);
                    }
                    if (data.StudentDailyReportInput[i].Sale != null)
                    {
                        TextBox textBox = new TextBox();
                        textBox.Width = 30;
                        textBox.ID = "sale" + i;
                        textBox.Text = data.StudentDailyReportInput[i].Sale;
                        //cellText = string.Format("<input style=\"width:30px\" id=\"sale" + i + "\" value= \"" + data.StudentDailyReportInput[i].Sale + "\" />");
                        bodyCell = BmTableSMS.AddCell(bodyRow, "", HorizontalAlign.Center);
                        bodyCell.Controls.Add(textBox);
                    }
                    else
                    {
                        TextBox textBox = new TextBox();
                        textBox.Width = 30;
                        textBox.ID = "sale" + i;
                        textBox.Text = "";
                        //cellText = string.Format("<input style=\"width:30px\" id=\"sale" + i + "\" value= \"\" />");
                        bodyCell = BmTableSMS.AddCell(bodyRow, "", HorizontalAlign.Center);
                        bodyCell.Controls.Add(textBox);
                    }
                }
            }
        }        protected void button1_Click(object sender, EventArgs e)
        {
            int count = Convert.ToInt32(this.rowCount.Value);
            //data = new StudentDailyReportSystem().GetDailyReportByUserID(cookieCompanyID, userID);
            //string str;
            //string stocks;
            //string sale;
            for (int i = 0; i < count; i++)
            {
                TextBox tb = (TextBox)this.FindControl("stocks" + i.ToString());
                string ss = tb.Text;
            }
                
            //    //string sss = tb.Text;
            //    //stocks = "0";
            //    //sale = "0";
            //    //str = "stocks" + i;
            //    //ClientScript.RegisterStartupScript(this.GetType(), "ccc", "<script>getValue('" + str + "')</script>");
            //    //stocks = this.valuehidden.Value.Trim();
            //    //str = "sale" + i;
            //    //ClientScript.RegisterStartupScript(this.GetType(), "ccc", "<script>getValue('" + str + "')</script>");
            //    //sale = this.valuehidden.Value.Trim();            //    //if (stocks == "" && sale == "")
            //    //{
            //    //    //data.StudentDailyReportInput[i].i
            //    //}
            //    //else
            //    //{
            //    //    data.StudentDailyReportInput[i].Stocks = stocks;
            //    //    data.StudentDailyReportInput[i].Sale = sale;
            //    //}            
            //new StudentDailyReportSystem().UpdateDailyReport(data);
        }        protected void button2_Click(object sender, EventArgs e)
        {
            Response.Redirect("DailyReport.aspx");
        }
    }
}
页面加载后，动态的textbox赋值正确，点button1后，取textbox得新值，取不到动态生成的控件了