C#压缩文件为ZIP格式

/// <summary>
        /// 功能：压缩文件（暂时只压缩文件夹下一级目录中的文件，文件夹及其子级被忽略）
        /// </summary>
        /// <param name="dirPath"> 被压缩的文件夹夹路径 </param>
        /// <param name="zipFilePath"> 生成压缩文件的路径，为空则默认与被压缩文件夹同一级目录，名称为：文件夹名 +.zip</param>
        /// <param name="err"> 出错信息</param>
        /// <returns> 是否压缩成功 </returns>
        public bool ZipFile(string dirPath, string zipFilePath, out string err)
        {
            err = "";
            if (dirPath == string.Empty)
            {
                err = "要压缩的文件夹不能为空！ ";
                return false;
            }
            if (!Directory.Exists(dirPath))
            {
                err = "要压缩的文件夹不存在！ ";
                return false;
            }
            //压缩文件名为空时使用文件夹名＋ zip
            if (zipFilePath == string.Empty)
            {
                if (dirPath.EndsWith("\\"))
                {
                    dirPath = dirPath.Substring(0, dirPath.Length - 1);
                }
                zipFilePath = dirPath + ".zip";
            }

            try
            {
                string[] filenames = Directory.GetFiles(dirPath);
                using (ZipOutputStream s = new ZipOutputStream(File.Create(zipFilePath)))
                {
                    s.SetLevel(9);
                    byte[] buffer = new byte[4096];
                    foreach (string file in filenames)
                    {
                        ZipEntry entry = new ZipEntry(Path.GetFileName(file));
                        entry.DateTime = DateTime.Now;
                        s.PutNextEntry(entry);
                        using (FileStream fs = File.OpenRead(file))
                        {
                            int sourceBytes;
                            do
                            {
                                sourceBytes = fs.Read(buffer, 0, buffer.Length);
                                s.Write(buffer, 0, sourceBytes);
                            } while (sourceBytes > 0);
                        }
                    }
                    s.Finish();
                    s.Close();
                }
            }
            catch (Exception ex)
            {
                err = ex.Message;
                return false;
            }
            return true;
        }

需要引用一个库文件：ICSharpCode.SharpZipLib.Zip.dll:https://download.youkuaiyun.com/download/qq_34576513/12718885