private PDFFileModel ListFiles(string path)
        {
            metaOnlyFile_ = new List <string>();
            PDFFileModel model = new PDFFileModel();

            model.Path = path;

            FileDirectory dir = new FileDirectory();

            dir.pathName = path;
            dir.name     = Path.GetFileName(path);
            dir.parent   = -1;
            model.Directories.Add(dir);

            //文件夹及子文件夹下的所有文件的全路径
            IEnumerable <string> files = Directory.EnumerateFileSystemEntries(path, "*.*", SearchOption.TopDirectoryOnly);

            foreach (string pathName in files)
            {
                ListFiles_r(model, pathName, 0);
            }

            return(model);
        }