我是新手，这个是做课件下载的·帮忙注释一下代码·特别是protected void LinkButton2_Click后面的，要很详细很详细的，谢谢各位的帮忙了

 protected void LinkButton1_Click(object sender, EventArgs e)
    {

    }
    protected void LinkButton2_Click(object sender, EventArgs e)
    {

        string filePath = Server.MapPath("File") + "\\" + Session["txt"].ToString();
        if (Session["txt"] != null)
        {
            if (System.IO.File.Exists(filePath))
            {
                FileInfo file = new FileInfo(filePath);
                Response.ContentEncoding = System.Text.Encoding.GetEncoding("UTF-8");                  Response.AddHeader("Content-Disposition", "attachment; filename=" + Server.UrlEncode(file.Name));                 Response.AddHeader("Content-length", file.Length.ToString());
                Response.ContentType = "appliction/octet-stream";
                Response.WriteFile(file.FullName);
                Response.End();
            }
        }


    }
    protected void ListBox3_SelectedIndexChanged(object sender, EventArgs e)
    {
        Session["txt"] = ListBox3.SelectedItem.Text.ToString();
    }
} --------------------编程问答-------------------- 文件下载，判断文件是否存在。然后调用WriteFile()把文件内容写入客户端。

补充：.NET技术 ,  C#