通过MS AJAX可以扩展一个服务器端控件在客户端呈现后的特性，使其界面更加友好。
        实例代码:IScriptControl.rar
        一、创建网站，选择ASP.NET AJAX-Enabled Web Site.
        二、向项目中添加一个类，使其派生自TextBox，并实现IScriptControl接口。如下代码实例：

public class SampleTextBox : TextBox, IScriptControl

         三、这个控件我们将实现两个属性：
               HighlightCssClass         控件得到焦点后的样式。当控件得到焦点的时候使其能够高亮显示。
               NoHighlightCssClass     失去焦点的控件的样式。

public string HighlightCssClass
        {
            get { return _highlightCssClass; }
            set { _highlightCssClass = value; }
        }

        public string NoHighlightCssClass
        {
            get { return _noHighlightCssClass; }
            set { _noHighlightCssClass = value; }
        }

        四、接口IScriptControl 的实现。
               GetScriptDescriptors()    返回一个包含控件客户端实例的属性和事件句柄的 ScriptDescriptor 类型的数组。
               GetScriptReferences()    返回一个包含控件客户端 JavaScript 代码的ScriptReference 类型的数组。
               在这个实例中，我们用四个函数来实现这两个函数。代码入下：
protected virtual IEnumerable<ScriptReference> GetScriptReferences()
        {
            ScriptReference reference = new ScriptReference();
            reference.Path = ResolveClientUrl("SampleTextBox.js");

            return new ScriptReference[] { reference };
        }

        protected virtual IEnumerable<ScriptDescriptor> GetScriptDescriptors()
        {
            ScriptControlDescriptor descriptor = new ScriptControlDescriptor("Samples.SampleTextBox", this.ClientID);
            descriptor.AddProperty("highlightCssClass", this.HighlightCssClass);
            descriptor.AddProperty("nohighlightCssClass", this.NoHighlightCssClass);

            return new ScriptDescriptor[] { descriptor };
        }

        IEnumerable<ScriptReference> IScriptControl.GetScriptReferences()
        {
            return GetScriptReferences();
        }

        IEnumerable<ScriptDescriptor> IScriptControl.GetScriptDescriptors()
        {
            return GetScriptDescriptors();
        }        五、这册控件。代码比较简单，所以就不再多加讲述，入下：
protected override void OnPreRender(EventArgs e)
        {
            if (!this.DesignMode)
            {
                // Test for ScriptManager and register if it exists
                sm = ScriptManager.GetCurrent(Page);

                if (sm == null)
                    throw new HttpException("A ScriptManager control must exist on the current page.");

                sm.RegisterScriptControl(this);
            }

            base.OnPreRender(e);
        }

        protected override void Render(HtmlTextWriter writer)
        {
            if (!this.DesignMode)
                sm.RegisterScriptDescriptors(this);

            base.Render(writer);
        }
         六、下边是我们新添加的类的完整代码：
using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Collections.Generic;

namespace TextBoxExtender
{
    /**//// <summary>
    /// SampleTextBox 的摘要说明
    /// </summary>
    public class SampleTextBox : TextBox, IScriptControl
    {
        private string _highlightCssClass;
        private string _noHighlightCssClass;
        private ScriptManager sm;

        public string HighlightCssClass
        {
            get { return _highlightCssClass; }
            set { _highlightCssClass = value; }
        }

        public string NoHighlightCssClass
        {
            get { return _noHighlightCssClass; }
            set { _noHighlightCssClass = value; }
        }

        protected override void OnPreRender(EventArgs e)
        {
            if (!this.DesignMode)
            {
                // Test for ScriptManager and register if it exists
                sm = ScriptManager.GetCurrent(Page);

                if (sm == null)
                    throw new HttpException("A ScriptManager control must exist on the current page.");

                sm.RegisterScriptControl(this);
            }

            base.OnPreRender(e);
        }

        protected override void Render(HtmlTextWriter writer)
        {
            if (!this.DesignMode)
                sm.RegisterScriptDescriptors(this);

            base.Render(writer);
        }

        protected virtual IEnumerable<ScriptReference> GetScriptReferences()
        {
            ScriptReference reference = new ScriptReference();
            reference.Path = ResolveClientUrl("SampleTextBox.js");

            return new ScriptReference[] { reference };
        }

        protected virtual IEnumerable<ScriptDescriptor> GetScriptDescriptors()
        {
            ScriptControlDescriptor descriptor = new ScriptControlDescriptor("Samples.SampleTextBox", this.ClientID);
            descriptor.AddProperty("highlightCssClass", this.HighlightCssClass);
            descriptor.AddProperty("nohighlightCssClass", this.NoHighlightCssClass);

            return new ScriptDescriptor[] { descriptor };
        }

        IEnumerable<ScriptReference> IScriptControl.GetScriptReferences()
        {
            return GetScriptReferences();
        }

        IEnumerable<ScriptDescriptor> IScriptControl.GetScriptDescriptors()
        {
            return GetScriptDescriptors();
        }
    }
}

         七、创建客户端控件。为客户端控件注册一个命名空间，并实现各个属性和事件：
// 为控件注册命名控件
Type.registerNamespace(Samples);

//
// 定义控件的属性
//
Samples.SampleTextBox = function(element) {
    Samples.SampleTextBox.initializeBase(this, [element]);

    this._highlightCssClass = null;
    this._nohighlightCssClass = null;
}

//
// 为控件创建属性
//

Samples.SampleTextBox.prototype = {

    initialize : function() {
        Samples.SampleTextBox.callBaseMethod(this, initialize);
       
        this._onfocusHandler = Function.createDelegate(this, this._onFocus);
        this._onblurHandler = Function.createDelegate(this, this._onBlur);

        $addHandlers(this.get_element(),
                     { focus : this._onFocus,
                       blur : this._onBlur },
                     this);
       
        this.get_element().className = this._nohighlightCssClass;
    },
   
    dispose : function() {
        $clearHandlers(this.get_element());
       
        Samples.SampleTextBox.callBaseMethod(this, dispose);
    },

    //
    // 事件委托
    //
   
    _onFocus : function(e) {
        if (this.get_element() && !this.get_element().disabled) {
            this.get_element().className = this._highlightCssClass;         
        }
    },
   
    _onBlur : function(e) {
        if (this.get_element() && !this.get_element().disabled) {
            this.get_element().className = this._nohighlightCssClass;         
        }
    },

    //
    // 控件属性
    //
   
    get_highlightCssClass : function() {
        return this._highlightCssClass;
    },

    set_highlightCssClass : function(value) {
        if (this._highlightCssClass !== value) {
            this._highlightCssClass = value;
            this.raisePropertyChanged(highlightCssClass);
        }
    },
   
    get_nohighlightCssClass : function() {
        return this._nohighlightCssClass;
    },

    set_nohighlightCssClass : function(value) {
        if (this._nohighlightCssClass !== value) {
            this._nohighlightCssClass = value;
            this.raisePropertyChanged(nohighlightCssClass);
        }
    }
}

// Optional descriptor for JSON serialization.
Samples.SampleTextBox.descriptor = {
    properties: [   {name: highlightCssClass, type: String},
                    {name: nohighlightCssClass, type: String} ]
}

// Register the class as a type that inherits from Sys.UI.Control.
Samples.SampleTextBox.registerClass(Samples.SampleTextBox, Sys.UI.Control);

if (typeof(Sys) !== undefined) Sys.Application.notifyScriptLoaded();

最后将如下代码复制到Default.aspx页面，用以测试空间：
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>
<%@ Register Namespace="TextBoxExtender" TagPrefix="sample" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
    <title>ASP.NET AJAX Control Sample</title>
    <style type="text/css">
    .LowLight
    {
        background-color:#EEEEEE;
    }
   
    .HighLight
    {
        background-color:Ivory;
    }
    </style>
</head>
<body>
    <form id="form1" runat="server">
        <asp:ScriptManager ID="ScriptManager1" runat="server" >
            <Scripts>
                <asp:ScriptReference Path="JScript.js" />
            </Scripts>
        </asp:ScriptManager>
        <div>
            <table border="0" cellpadding="2">
              <tr>
                <td><asp:Label runat="server" ID="Label1" AssociatedControlID="TextBox1">Name</asp:Label></td>
                <td><sample:SampleTextBox ID="TextBox1" runat="server" NoHighlightCssClass="LowLight" HighlightCssClass="HighLight" /></td>
              </tr>
              <tr>
                <td><asp:Label runat="server" ID="Label2" AssociatedControlID="TextBox2">Phone</asp:Label></td>
                <td><sample:SampleTextBox ID="TextBox2" runat="server" NoHighlightCssClass="LowLight" HighlightCssClass="HighLight" /></td>
              </tr>
              <tr>
                <td><asp:Label runat="server" ID="Label3" AssociatedControlID="TextBox3">E-mail</asp:Label></td>
                <td><sample:SampleTextBox ID="TextBox3" runat="server" NoHighlightCssClass="LowLight" HighlightCssClass="HighLight" /></td>
              </tr>
            </table>
           
            <asp:Button runat="server" ID="Button1" Text="Submit Form" />
        </div>
    </form>
</body>
</html>
http://www.cnblogs.com/hblynn/archive/2007/01/29/633619.html