Dynamically adding controls to a content page

I have a content page I would like to be able to add controls dynamically to this page. 
 
1 <%@ Page Language="C#" MasterPageFile="~/Layouts/Scriptlet.master" AutoEventWireup="true" CodeFile="Preview.aspx.cs" Inherits="Admin_Customize_Preview" Title="Untitled Page" %>
2 "Content1" ContentPlaceHolderID="PageContent" Runat="Server">
 I've tried code snippets like these but to no avail:- 1 this.controls.add(new TextBox()) ; ...