private void button1_Click(object sender, EventArgs e)
        {
            string URL = txtSourceDir.Text;
            string filename = txtDestDir.Text;

            if (DownloadFile(@"http://10.10.1.137/bjh/门禁管理系统/K6-SETUP/CDROM/Disk1/setup.exe", @"C:\setup.exe", progressBar1, label3))
            {
                MessageBox.Show("下载成功！");
                this.Close();
            }
            else
                MessageBox.Show("下载失败！");
        }

public bool DownloadFile(string URL, string filename, ProgressBar prog, Label label1)
        {
            float percent = 0;
            try
            {
                HttpWebRequest Myrq = (HttpWebRequest)WebRequest.Create(URL);
                Myrq.Timeout = 5000;
                HttpWebResponse myrp = (HttpWebResponse)Myrq.GetResponse();

                myrp.Close();
                long totalBytes = myrp.ContentLength;
                if (prog != null)
                {
                    prog.Maximum = (int)totalBytes;
                }
                Stream st = myrp.GetResponseStream();
                Stream so = new FileStream(filename, FileMode.Create);
                long totalDownloadedByte = 0;
                byte[] by = new byte[1024];
                int osize = st.Read(by, 0, (int)by.Length);
                while (osize > 0)
                {
                    totalDownloadedByte = osize + totalDownloadedByte;
                    Application.DoEvents();
                    so.Write(by, 0, osize);
                    if (prog != null)
                    {
                        prog.Value = (int)totalDownloadedByte;
                    }
                    osize = st.Read(by, 0, (int)by.Length);

                    percent = (float)totalDownloadedByte / (float)totalBytes * 100;
                    label3.Text = "当前补丁下载进度" + percent.ToString() + "%";
                    Application.DoEvents(); //必须加注这句代码，否则label1将因为循环执行太快而来不及显示信息
                }
                so.Close();
                st.Close();
                myrp.Close();
            }
            catch (System.Exception)
            {
                return false;
            }

            return true;
        }