class classDownloader
    {
        private string strURL;  //待下载文件链接
        private string strSavePath; //待下载文件存放路径
        private long lContentLenth = 0; //文件的大小
        private long lStartPos = 0; //文件下载的起始位置
        private System.IO.FileStream fs;
        private System.IO.Stream ns;
        private System.Net.HttpWebRequest request;
        private System.Net.WebRequest req;
        private const int NBuff = 512;//下载流缓冲池大小
        private void SetURL(string temp)    //获取待下载文件链接
        {
            strURL = temp;
        }
        private void SetSavePath(string temp)   //获取待下载文件存放路径
        {
            strSavePath = temp;
        }
        private void  StartDownload() //开始下载
        {
            //打开网络连接
            try
            {
               // req = System.Net.HttpWebRequest.Create(strURL);
               // req.Method = "HEAD";
                 request = (System.Net.HttpWebRequest)System.Net.HttpWebRequest.Create(strURL);
                 System.Net.WebResponse resp = request.GetResponse();
                 long.TryParse(resp.Headers.Get("Content-Length"), out lContentLenth);//获取待下载文件的大小
                //判断是新文件或续传文件或已经下好了
                if (System.IO.File.Exists(strSavePath))
                {
                    fs = System.IO.File.OpenWrite(strSavePath);
                    lStartPos = fs.Length;
                    if (lStartPos >= lContentLenth)
                    {
                        MessageBox.Show("已经下好了");
                        return;
                    }
                    //lStartPos -= 10240;
                    fs.Seek(lStartPos, System.IO.SeekOrigin.Current);
                }
                else
                {
                    fs = new System.IO.FileStream(strSavePath, System.IO.FileMode.Create);
                    lStartPos = 0;
                }
                if (lStartPos > 0)
                {
                    request.AddRange((int)lStartPos);   //设置range值
                }
                //向服务器请求，获得服务器回应数据流
                 ns = request.GetResponse().GetResponseStream();
                byte[] nbytes = new byte[NBuff];
                int nReadSize = 0;
                nReadSize = ns.Read(nbytes, 0, NBuff);
                while (nReadSize > 0)
                {
                    fs.Write(nbytes, 0, nReadSize);
                    nReadSize = ns.Read(nbytes, 0, NBuff);
                    Program.a.progressBar1.Value = (int)(((float)fs.Length / (float)lContentLenth) * 100);
                    int resault = (int)((float)fs.Length / (float)lContentLenth*100);
                    Program.a.label2.Text = "已下载" + resault+"%";
                    //Program.a.label2.Text = "已下载" + fs.Length + "/" + lContentLenth;
                }
                //MessageBox.Show("下载完成");
            }
            catch (Exception ex)
            {
                MessageBox.Show("下载中出错" + ex.ToString());
            }
            finally
            {
                if (!(lStartPos >= lContentLenth))
                {
                    ns.Close();
                    fs.Close();
                }
                //req.Abort();
                request.Abort();
            }
        }
        public void update()
        {

            classWebRequest webrequest = new classWebRequest();
            webrequest.WebReqVer();
            /*
            DataSet dataset = new DataSet();
            DataTable datatable = new DataTable("UpdataContext");
            datatable.Columns.Add(new DataColumn ("No.",typeof (int)))