How to pass variable to SelectCommand of SqlDataSource? Not Working Please help

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" DataKeyNames="id"
                    DataSourceID="SqlDataSource1" AllowPaging="True" AllowSorting="True">
                    <Columns>
                        <asp:BoundField DataField="id" HeaderText="id" ReadOnly="True" SortExpression="id" />
                        <asp:BoundField DataField="Question" HeaderText="Question" SortExpression="Question" />
                        <asp:TemplateField>
                            <ItemTemplate>
                                <asp:RadioButtonList AutoPostBack="true" ID="rbl" runat="server" Enabled="true" SelectedIndex='<%#Convert.ToInt32(DataBinder.Eval(Container.DataItem , "Discontinued"))%>'
                                    OnSelectedIndexChanged="rbl_SelectedIndexChanged">
                                    <asp:ListItem Value="0">No</asp:ListItem>
                                    <asp:ListItem Value="1">Yes</asp:ListItem>
                                </asp:RadioButtonList>
                            </ItemTemplate>
                        </asp:TemplateField>
                    </Columns>
                </asp:GridView>

<asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:studentConnectionString %>"

                    SelectCommand="SELECT * FROM [AddQustSrvs] where [Category]='Food' and [UserId]= @userId "
                    UpdateCommand="UPDATE [AddQustSrvs] SET [Discontinued] = @Discontinued WHERE [id] = @id">
                    <SelectParameters>
                        <asp:Parameter DefaultValue="'<%= userid %>'" Name="userId" DbType="String" />
                    </SelectParameters>
                    <UpdateParameters>
                        <asp:Parameter Name="Discontinued" Type="Boolean" />
                        <asp:Parameter Name="id" Type="Int32" />
                    </UpdateParameters>
                </asp:SqlDataSource>