(一). 概述
         示例制作一个与Asp.net TextBox同样功能的 TextBox control, 可以了解一下
        Control底层的实现原理
(二). 代码实现
      1. 核心控件生成代码文件TextBox.cs
 1  1using System;
 2  2using System.Data;
 3  3using System.Configuration;
 4  4using System.Web;
 5  5using System.Web.Security;
 6  6using System.Web.UI;
 7  7using System.Web.UI.WebControls;
 8  8using System.Web.UI.WebControls.WebParts;
 9  9using System.Web.UI.HtmlControls;
10 10
11 11using System.Text;
12 12using System.Collections.Specialized;
13 13
14 14namespace KingControls
15 15{
16 16    /**//// <summary>
17 17    /// Making a TextBox WebControl    
18 18    /// </summary>
19 19    public class TextBox : Control, IPostBackDataHandler  //IPostBackDataHandler: 处理回发数据使用
20 20    {
21 21        public TextBox()
22 22        {
23 23        }
24 24
25 25        /**//// <summary>
26 26        /// 设置或获取显示文本
27 27        /// </summary>       
28 28        public string Text
29 29        {
30 30            //Web编程中要用ViewState为两次回发共享数据
31 31            get
32 32            {
33 33                String s = (String)ViewState["Text"];
34 34                return ((s == null) ? String.Empty : s);
35 35            }
36 36
37 37            set
38 38            {
39 39                ViewState["Text"] = value;
40 40            }
41 41        }
42 42
43 43        /**//// <summary>
44 44        /// 生成呈现Html格式标记
45 45        /// </summary>
46 46        /// <param name="writer"></param>
47 47        protected override void Render(HtmlTextWriter writer)
48 48        {
49 49            StringBuilder sb = new StringBuilder();
50 50            sb.Append("<input type=\"text\" name=");
51 51            sb.Append("\"" + UniqueID + "\""); //标识符，继承自基类Control
52 52            sb.Append("value=");
53 53
54 54            //HttpUtility.HtmlEncode 将用户输入字串转换成Html格式，主要转义用户输入的html关键字为非html关键字字符
55 55            sb.Append("\"" + HttpUtility.Html