编辑时获取DataList前台参数

Question

                <asp:DataList ID="DataList" runat="server">
                    <EditItemTemplate>
                        <table>
                            <tr>
                                <td rowspan="5" height="70px" width="101px">
                                    <asp:Label ID="photo" runat="server" Text='<%#Eval("photo") %>'></asp:Label>
                                </td>
                                <td height="25" align="right" width="92px">
                                    用户名 ：
                                </td>
                                <td height="25" align="left" width="116px">
                                    <asp:TextBox ID="username" runat="server" Text='<%#DataBinder.Eval(Container.DataItem,"username") %>'></asp:TextBox>
                                </td>
                            </tr>
                            
                            
                           
                           
                        </table>
                    </EditItemTemplate>
                </asp:DataList>以上是我前台的代码，我想在后台编辑的时候获得TextBox框里的参数，怎么获取？