做一个按钮读取文件下载

System.IO.FileInfo fileInfo = new System.IO.FileInfo(fileName);
   System.Web.HttpContext.Current.Response.AddHeader("Content-Disposition","attachment;filename="+ fileInfo.Name);
   System.Web.HttpContext.Current.Response.AddHeader("Content-Length",fileInfo.Length.ToString());
   System.Web.HttpContext.Current.Response.Charset = "UTF-8";
   System.Web.HttpContext.Current.Response.ContentType = "application/octet-stream";
   byte[] buffer = new byte[fileInfo.Length];
   using(System.IO.FileStream fileStream = fileInfo.OpenRead())
   {
    fileStream.Read(buffer,0,buffer.Length);
   }
   System.Web.HttpContext.Current.Response.BinaryWrite(buffer);
   System.Web.HttpContext.Current.Response.Flush();