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();
                 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[];
                 for (int i = ; 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, , buffer.Length);
                             ZipStream.Write(buffer, , sourceBytes);
                         } while (sourceBytes > );
                     }
                 }
                 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