文件夹过滤非法字符

private static string RemoveInvalidFileNameChars(string fileName)
        {
            if (string.IsNullOrWhiteSpace(fileName)) return null;

            string invalid = new string(Path.GetInvalidFileNameChars()) + new string(Path.GetInvalidPathChars());
            StringBuilder sb = new StringBuilder();
            //foreach (char c in invalid) {fileName = fileName.Replace(c.ToString(), "");}
            foreach (char c in fileName)
            {
                if (!invalid.Contains(c)) sb.Append(c);
            }
            return sb.ToString();
        }