FindControl

Question

我在单元格里动态添加了RadioButtonList 控件，ID也赋值了，生成控件的代码如下：
                      RadioButtonList tempRadio = new RadioButtonList();                    tempRadio.ID =iRoleID.ToString();
                    for (int j = 0; j < lstUserList.Count; j++)
                    {
                        dcModUserList = lstUserList[j];
                        ListItem li = new ListItem();                        li.Text = dcModUserList.UserName;
                        li.Value = dcModUserList.UserName;                        tempRadio.Items.Add(new ListItem(dcModUserList.UserName, dcModUserList.UserName));
                    }
                    tdPeopleList.Controls.Add(tempRadio);
实例RadioButtonList 的代码如下：tdPeopleList为单元格的ID
     RadioButtonList  tempRadio = (RadioButtonList)tdPeopleList.FindControl("sId");
结果取出来的tempRadio=null
不知道为什么