关于模版列中 DropDownExtender的问题

[wzllin]

<asp:TemplateField HeaderText="单价">
                                                <ItemTemplate>                                                 <asp:UpdatePanel ID="UpdatePanel1" runat="server">  <ContentTemplate>       
     <asp:TextBox  ID="txtckj" runat="server"></asp:TextBox> 
      <asp:Panel ID="Panel1" runat="server" Style="display :none; visibility: hidden;" CssClass="ContainPanel"> 
      </asp:Panel>
     <ajaxToolkit:DropDownExtender ID="ddlckj" runat="server" TargetControlID ="txtckj" DropDownControlID="Panel1">
        </ajaxToolkit:DropDownExtender>
        </ContentTemplate>
     </asp:UpdatePanel>                                           </ItemTemplate>
                                                <HeaderStyle Width="10%" />
                                            </asp:TemplateField>
      

    protected void gvKC_RowDataBound(object sender, GridViewRowEventArgs e)
    {
        if (((TextBox)e.Row.FindControl("txtckj")) != null)
        {
            UpdatePanel UpdatePanel = (UpdatePanel)e.Row.FindControl("UpdatePanel1");          
            string ymbh = ((Label)e.Row.FindControl("lblymbh")).Text;
            string sql;
            sql = " SELECT  dj from table ";
            DataSet ds;
            ds = SqlHelper.DataSet(SqlHelper.connectionString, CommandType.Text, sql);     
            for(int i=0;i<=ds.Tables[0].Rows.Count-1;i++)
            {
                LinkButton lbtn = new LinkButton();
                lbtn.ID = ymbh + i.ToString();
                lbtn.Text = ds.Tables[0].Rows[i]["dj"].ToString();
                lbtn.Click += new EventHandler(lbtn_Click);
                lbtn.CssClass = "link";
                
                Panel1.Controls.Add(lbtn);
                AsyncPostBackTrigger trigger = new AsyncPostBackTrigger();
                trigger.ControlID = lbtn.ID;
                trigger.EventName = "Click";
                UpdatePanel.Triggers.Add(trigger);
            }
        }
    }

    private void lbtn_Click(object sender, EventArgs e)
    {
    
        txtckj.Text = (sender as LinkButton).Text;
    }

为什么单击每一个下拉项时，txtckj没有被赋值

[wzllin]

?????????????????/

[wzllin]

？？？？？？？？？？？