下载弹出提示框

有个朋友问我下载弹出提示框的写法，具体如下：

出现提示框

string strFile="F://a.doc";//路径根据实际情况而定
if(!System.IO.File.Exists(strFile))
   {
    Response.Write("<script language='javascript'>alert('对不起，文件不存在！');</script>");
    return;
   }
   Response.Clear();
   Response.ClearHeaders();
   Response.Charset = "GB2312";
   Response.ContentEncoding =System.Text.Encoding.UTF8;
   Response.ContentType = "application/octet-stream"; 
   FileInfo fi=new FileInfo(strFile);
   Response.AddHeader("Content-Disposition","attachment;  filename="  +  HttpUtility.UrlEncode(fi.Name)) ;
   Response.AddHeader("Content-Length",fi.Length.ToString());
   byte[] tmpbyte=new byte[1024*8];
   FileStream fs=fi.OpenRead();
   int count;
   while((count=fs.Read(tmpbyte,0,tmpbyte.Length))>0)
   {
    Response.BinaryWrite(tmpbyte);
    Response.Flush();
   }
   fs.Close();   
   Response.End();

直接在浏览器中打开
   string strFile="F://a.doc";//路径根据实际情况而定
   Response.Clear();
   Response.ClearHeaders();
   Response.Charset = "GB2312";
   Response.ContentEncoding =System.Text.Encoding.UTF8;
   Response.ContentType = "application/msword"; 
   Response.WriteFile(strFile);