一、首先下載引用“ICSharpCode.SharpZipLib.dll”

二、字串壓縮

 /// <summary>
        /// 將傳入的二進位制字串資料以Zip演算法解壓縮
        /// </summary>
        /// <param name="zippedString">經GZip壓縮後的二進位制字串</param>
        /// <returns>原始未壓縮字串</returns>
        public static string ZipDecompressString(this string zippedString)
        {
            if (string.IsNullOrEmpty(zippedString) || zippedString.Length == 0)
            {
                return "";
            }
            else
            {
                string dummyData = zippedString;
                dummyData = dummyData.Trim().Replace("%", "").Replace(",", "").Replace(" ", "+").Replace("\"", "").Replace("\\n", "");

                //}
                byte[] b = Convert.FromBase64String(dummyData);
                using (MemoryStream from = new MemoryStream(b))
                using (ZipInputStream zip = new ZipInputStream(from))
                using (MemoryStream to = new MemoryStream())
                {
                    ZipEntry entry = zip.GetNextEntry();
                    byte[] buffer = new byte[1024];
                    int len = 0;
                    while ((len = zip.Read(buffer, 0, buffer.Length)) > 0)
                    {
                        to.Write(buffer, 0, len);
                    }
                    b = to.ToArray();
                    return Encoding.UTF8.GetString(b);
                }
            }
        }

三、壓縮字串解壓

/// <summary>
        /// 將傳入字串以Zip演算法壓縮後，返回utf-8格式Base64編碼字元
        /// </summary>
        /// <param name="rawString">需要壓縮的字串</param>
        /// <returns>壓縮後的Base64編碼的字串</returns>
        public static string ZipCompressString(this string rawString)
        {
            if (string.IsNullOrEmpty(rawString) || rawString.Length == 0)
            {
                return "";
            }
            else
            {
                byte[] rawData = System.Text.Encoding.UTF8.GetBytes(rawString);
                using (MemoryStream to = new MemoryStream())
                using (ZipOutputStream zip = new ZipOutputStream(to))
                {
                    ZipEntry entry = new ZipEntry("ToBase64String");
                    zip.PutNextEntry(entry);

                    zip.Write(rawData, 0, rawData.Length);
                    zip.CloseEntry();  // 必須，否則報不可預料的壓縮檔案末端
                    zip.Finish();      // 必須，否則報這個壓縮檔案格式未知或者資料已經被損壞
                    return Convert.ToBase64String(to.ToArray());
                }
            }
        }