winform ProgressBar

之前没用过ProgressBar，前几天做数据下载当时测试用的下载文件比较小，基本上不显示进度条，后来发现可以设置每次下载的量，如果非想看到进度条的话，代码如下：

 public class DownFile
    {
        public delegate void DownFileDelegate();
        public event DownFileDelegate onDownFileCompleted;
        public String DownFileName;

        public void DownloadFile(string URL, string filename, System.Windows.Forms.ProgressBar prog)
        {
            try
            {
                DownFileName = filename;
                prog.Show();
                System.Net.HttpWebRequest Myrq = (System.Net.HttpWebRequest)System.Net.HttpWebRequest.Create(URL);
                System.Net.HttpWebResponse myrp = (System.Net.HttpWebResponse)Myrq.GetResponse();
                
                long totalBytes = myrp.ContentLength;

                if (prog != null)
                {
                    prog.Maximum = (int)totalBytes;
                }

                System.IO.Stream st = myrp.GetResponseStream();
                System.IO.Stream so = new System.IO.FileStream(filename, System.IO.FileMode.Create);
                long totalDownloadedByte = 0;
                int size = prog.Maximum / 1000;
                byte[] by = new byte[size];
                int osize = st.Read(by, 0, (int)by.Length);
                while (osize > 0)
                {
                    totalDownloadedByte = osize + totalDownloadedByte;
                    System.Windows.Forms.Application.DoEvents();
                    so.Write(by, 0, osize);

                    if (prog != null)
                    {
                        prog.Value = (int)totalDownloadedByte;
                        prog.PerformStep();
                        
                    }
                    osize = st.Read(by, 0, (int)by.Length);
                }
               
                so.Close();
                st.Close();
                myrp.Close();
                if (prog.Value == prog.Maximum)
                {
                    if (onDownFileCompleted != null)
                    {
                        onDownFileCompleted();
                    }
                }
            }
            catch (System.Exception)
            {
                throw;
            }
        }
    }