用户控件获得数据的有关问题

 public partial class UcCreatTable : System.Web.UI.UserControl    {        int Count        {            get            {                if (ViewState["ControlCount"] == null)                    ViewState["ControlCount"] = 0;                return (int)ViewState["ControlCount"];            }            set            {                ViewState["ControlCount"] = value;            }        }        protected void Page_Load(object sender, EventArgs e)        {        }        protected void ImgBtnAddField_Click(object sender, ImageClickEventArgs e)        {            Count++;            for (int i = 0; i < Count; i++)            {                string[] drpItems = { "请选择字段类型", "int", "nvchar", "datetime" };                Label lb1 = new Label();                lb1.Text = "字段";                lb1.ID = ClientID;                PlaceHolder1.Controls.Add(lb1);                TextBox txt = new TextBox();                txt.ID = ClientID;                txt.Text = "";                PlaceHolder1.Controls.Add(txt);                Label lb2 = new Label();                lb2.Text = "字段";                lb2.ID = ClientID;                PlaceHolder1.Controls.Add(lb2);                DropDownList drplist = new DropDownList();                drplist.ID = ClientID;                foreach (string item in drpItems)                {                    drplist.Items.Add(item);                }                PlaceHolder1.Controls.Add(drplist);                Literal lt1 = new Literal();                lt1.ID = ClientID;                lt1.Text = "<br/>";                PlaceHolder1.Controls.Add(lt1);            }        }                   }

Control plh = UcCreatTable1.FindControl("PlaceHolder1");            Control txt = UcCreatTable1.FindControl("txtTableName");           Label1.Text= plh.GetType().ToString();           Label2.Text = txt.ID.ToString();            //三层调用插入数据没问题，现在就是不能获取数据           foreach (Control ctl in plh.Controls)           {               Field field1 = new Field();               field1.Field_TableName = ((TextBox)txt).Text;               Literal1.Text = ((TextBox)txt).Text.ToString();               if (ctl.GetType().ToString().Equals("System.Web.UI.WebControls.TextBox") && ctl.ID != null)               {                   field1.Field_FieldName = ((TextBox)ctl).Text;                   Literal2.Text = ((TextBox)ctl).Text.ToString();               }               if (ctl.GetType().ToString().Equals("System.Web.UI.WebControls.Lable") && ctl.ID != null)               {                   field1.Field_Type = ((DropDownList)ctl).Text;                   Literal3.Text = ((DropDownList)ctl).Text.ToString();               }               new FieldBll().AddNews(field1);           }        }