(服务器端的代码的实现)当页面上的某个控件回发时，保持滚动条位置的。

using System;
using System.IO;
using System.Text;
using System.Text.RegularExpressions;
using System.Web.UI;

public partial class Email_Default : System.Web.UI.Page
{
private bool _useScrollPersistence = true;

    /// <summary>
    /// There could be PostBack senarios where we do not want to remember the scroll position. Set this property to false
    /// if you would like the page to forget the current scroll position
    /// </summary>

    public bool UseScrollPersistence
    {
        get { return this._useScrollPersistence; }
        set { this._useScrollPersistence = value; }
    }

private string _bodyID;

    /// <summary>
    /// Some pages might already have the ID attribute set for the body tag. Setting this property will not render the ID or change
    /// the existing value. It will simply update the javascript written out to the browser.
    /// </summary>
    public string BodyID
    {
        get { return this._bodyID; }
        set { this._bodyID = value; }
    }

    //Last chance. Do we want to maintain the current scroll position
    protected override void OnPreRender(EventArgs e)
    {
        if (UseScrollPersistence)
        {
            RetainScrollPosition();
        }
        base.OnPreRender(e);
    }

    protected override void Render(HtmlTextWriter writer)
    {
        //No need processing the HTML if the user does not want to maintain scroll position or already has
        //set the body ID value
        if (UseScrollPersistence && BodyID == null)
        {
            TextWriter tempWriter = new StringWriter();
            base.Render(new HtmlTextWriter(tempWriter));
            writer.Write(Regex.Replace(tempWriter.ToString(), "<body", "<body id=\"thebody\" ", RegexOptions.IgnoreCase));
        }
        else
        {
            base.Render(writer);
        }
    }

private static string saveScrollPosition = "<script language='javascript'>function saveScrollPosition() {{document.forms[0].__SCROLLPOS.value = {0}.scrollTop;}}{0}.onscroll=saveScrollPosition;</script>";
private static string setScrollPosition = "<script language='javascript'>function setScrollPosition() {{{0}.scrollTop =\"{1}\";}}{0}.onload=setScrollPosition;</script>";

    //Write out javascript and hidden field
    private void RetainScrollPosition()
    {
        RegisterHiddenField("__SCROLLPOS", "0");
        string __bodyID = BodyID == null ? "thebody" : BodyID;
        RegisterStartupScript("saveScroll", string.Format(saveScrollPosition, __bodyID));

        if (Page.IsPostBack)
        {
            RegisterStartupScript("setScroll", string.Format(setScrollPosition, __bodyID, Request.Form["__SCROLLPOS"]));
        }
    }
}