动态添加控件，如何实现点击一次添加一个，再次点击再增加一个。。。

                                <table style="width: 100%" border="1" runat="server" id="mx">

                                    <tr>

                                        <td align="left" style="width: 100px;">

                                            姓名：

                                        </td>

                                        <td align="left">

                                            <asp:TextBox ID="TextBox23" CssClass="underline" Width="100px" runat="server"></asp:TextBox>

                                        </td>

                                        <td align="left" colspan="2">

                                            身份证号：

                                            <asp:TextBox ID="TextBox24" runat="server" 

                                            CssClass="underline" Width="100px"></asp:TextBox>

                                            <asp:Button  ID="Button2" runat="server" Font-Size="12px" Text="添加一行" OnClick="AddNew" />

                                        </td>

                                    </tr>

                                </table>

        protected void AddNew(object sender, EventArgs e)

        {

            HtmlTableRow row = new HtmlTableRow();

            HtmlTableCell cell;

            TextBox tb;



            cell = new HtmlTableCell();

            cell.InnerText = "姓名：";

            row.Cells.Add(cell);



            cell = new HtmlTableCell();

            tb = new TextBox();

            tb.ID = "tb" + mx.Rows.Count.ToString();

            tb.CssClass = "underline";

            tb.Width = Unit.Pixel(100);

            tb.Font.Size = FontUnit.Point(9);

            cell.Controls.Add(tb);

            row.Cells.Add(cell);



            cell = new HtmlTableCell();

            tb = new TextBox();

            tb.ID = "tb_" + mx.Rows.Count.ToString();

            tb.CssClass = "underline";

            tb.Width = Unit.Pixel(100);

            tb.Font.Size = FontUnit.Point(9);

            cell.Controls.Add(tb);



            cell = new HtmlTableCell();

            cell.InnerText = "身份证号：";

            tb = new TextBox();

            tb.ID = "tb__" + mx.Rows.Count.ToString();

            tb.CssClass = "underline";

            tb.Width = Unit.Pixel(100);

            tb.Font.Size = FontUnit.Point(9);

            cell.Controls.Add(tb);

            



            row.Cells.Add(cell);

            mx.Rows.Add(row);

            

            

        }

我想在每次点击“添加一行”的按钮后就添加一个新行，点几次，就添加几行
但是上面的代码只是实现了一行，第二次点击时候就不添加。。。。