求 AJAX 无刷新多文件上传示例,该怎么处理

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.IO; //Directory, Path, FileInfousing System.Text; //StringBuilderpublic partial class _Default : System.Web.UI.Page {    private const string TARGET_DIR = "~/";    protected void btnSubmit_Click(object sender, EventArgs e)    {        //Check target directory        string sTargetDir = Request.MapPath(TARGET_DIR);        System.Diagnostics.Debug.Assert(Directory.Exists(sTargetDir));        StringBuilder objDisplay = new StringBuilder();        objDisplay.Append("<h3>You have just saved:</h3><ul>");                //Iterate through posted files (foreach does not work with empty file inputs)        for (int i = 0; i < Request.Files.Count; i++)        {            HttpPostedFile objFile = Request.Files[i];            //Make sure file input has content            if ((objFile.ContentLength > 0) && (objFile.FileName.Length > 0))            {                //Get target file path for save as                string sFileName = Path.GetFileName(objFile.FileName);                string sFilePath = Path.Combine(sTargetDir, sFileName);                FileInfo objFileInfo = new FileInfo(sFilePath);                //No business rule, i.e. we just want to avoid failure                if (objFileInfo.Exists)                {                    objFileInfo.Attributes &= ~FileAttributes.ReadOnly;                    objFileInfo.Delete();                }                //Save file                objFile.SaveAs(sFilePath);                //Append link                objDisplay.AppendFormat("<li><a href=\"{0}\">{1}</a></li>",                    this.ResolveUrl(Path.Combine(TARGET_DIR, sFileName)),                    sFileName);            }        }        objDisplay.Append("</ul>");        litDisplay.Text = objDisplay.ToString();    }}