C# 取文本中间

        /// <summary>
        /// 取中间文本
        /// </summary>
        /// <param name="SumString">总文本</param>
        /// <param name="LeftString">左边文本</param>
        /// <param name="RightString">右边文本</param>
        /// <returns>找到返回取出的中间文本，没找到返回空</returns>
        public static string GetMiddleString(string SumString, string LeftString, string RightString)
        {
            if (string.IsNullOrEmpty(SumString)) return "";
            if (string.IsNullOrEmpty(LeftString)) return "";
            if (string.IsNullOrEmpty(RightString)) return "";

            int LeftIndex = SumString.IndexOf(LeftString);
            if (LeftIndex == -1) return "";
            LeftIndex = LeftIndex + LeftString.Length;
            int RightIndex = SumString.IndexOf(RightString, LeftIndex);
            if (RightIndex == -1) return "";
            return SumString.Substring(LeftIndex, RightIndex - LeftIndex);
        }