HttpWebRequest下载文件带进度条

Code
 1/**//// <summary>
 2        /// 下载文件到本地
 3        /// </summary>
 4        /// <param name="url"></param>
 5        /// <param name="filePath"></param>
 6        public static void DownloadFile(string url, string localPath, ProgressBar bar)
 7        {
 8            try
 9            {
10                bar.Value = bar.Minimum;
11
12                HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(url);
13                HttpWebResponse resp = (HttpWebResponse)req.GetResponse();
14
15                long totalBytes = resp.ContentLength;
16                bar.Maximum = (int)totalBytes;
17
18                using (Stream sResp = resp.GetResponseStream())
19                {
20                    if (!Directory.Exists(localPath.Substring(0, localPath.LastIndexOf('\\'))))
21                        Directory.CreateDirectory(localPath.Substring(0, localPath.LastIndexOf('\\')));
22                    using (Stream sFile = new FileStream(localPath, FileMode.Create))
23                    {
24                        long totalDownloadBytes = 0;
25                        byte[] bs = new byte[1024];
26                        int size = sResp.Read(bs, 0, bs.Length);
27                        while (size > 0)
28                        {
29                            totalDownloadBytes += size;
30                            App.DoEvents();
31                            sFile.Write(bs, 0, size);
32                            bar.Value = (int)totalDownloadBytes;
33                            size = sResp.Read(bs, 0, bs.Length);
34                        }
35                    }
36                }
37                bar.Value = bar.Maximum;
38            }
39            catch (Exception ex)
40            {
41                throw ex;
42            }
43        }