使用 ICharpCode.SharpZipLib 压缩指定目录结构

今天做项目中遇见一个压缩问题，我的目录结构是树形菜单，文件在服务器存储是平面存储，没有目录结构，所以在下载指定目录的时候要构建目录结构，如下：

当我右键点击下载b目录文件夹的时候要Download  b 目录下的所有文件，并且有目录结构，实现如下：

        public static void CreateZip(List<string> directories, List<string> filenames, string zipFileName, string dir)
        {
            using (ZipOutputStream ZipStream = new ZipOutputStream(System.IO.File.Create(dir + zipFileName)))
            {
                ZipStream.SetLevel(9);
                ZipEntryFactory factory = new ZipEntryFactory();
                foreach (var directory in directories)
                {
                    string virtualDirectory = directory;
                    ZipEntry zipEntry = factory.MakeDirectoryEntry(virtualDirectory);
                    zipEntry.DateTime = DateTime.Now;
                    ZipStream.PutNextEntry(zipEntry);
                }

                byte[] buffer = new byte[4096];
                for (int i = 0; i < filenames.Count; i++)
                {
                    string file = filenames[i];
                    string newfileName = file.Replace(dir, string.Empty);
                    ZipEntry entry = factory.MakeFileEntry(directories[i] + "//" + newfileName);

                    entry.DateTime = DateTime.Now;
                    ZipStream.PutNextEntry(entry);

                    using (FileStream fs = System.IO.File.OpenRead(file))
                    {
                        int sourceBytes;
                        do
                        {
                            sourceBytes = fs.Read(buffer, 0, buffer.Length);
                            ZipStream.Write(buffer, 0, sourceBytes);
                        } while (sourceBytes > 0);
                    }
                }
                ZipStream.Finish();
                ZipStream.Close();
            }

            System.Web.HttpContext.Current.Response.ContentType = "application/x-compress zip";
            System.Web.HttpContext.Current.Response.AddHeader("Content-Disposition", "attachment;filename=" + zipFileName);
            System.Web.HttpContext.Current.Response.TransmitFile(dir + zipFileName);
        }

以下载b目录为例，参数如下：
directories：

filenames：

zipFileName: 

 dir:

调用上面方法传入正确参数即可生成正确的目录