#region GetDataTable 返回部分行数据用于分页 
        /// <summary>
        /// GetDataTable 返回部分行数据 先定义好排序字段
        /// </summary>
        /// <param name="strSql">sql语句</param>
        /// <param name="parameters">参数([string parameterName,object Value])</param>        
        ///<param name="page">第几页</param>
        ///<param name="num">每页几条数据</param>
        /// <returns>部分数据行</returns>
        public DataTable GetDataTable(string strSql, int page ,int num, Dictionary<string, object> parameters)
        {
            DataTable seldt = new DataTable();
            using (SqlConnection connection = new SqlConnection(connectionString))
            {
                connection.Open();
                using (SqlCommand cmd = new SqlCommand())
                {
                    try
                    {
                        cmd.Connection = connection;
                        cmd.CommandType = CommandType.Text;
                        //sqlserver 2012 分页写法 https://www.cnblogs.com/godbell/p/7260704.html                         
                        strSql += " offset  " + (num-1) * page + "  rows fetch next " + num + " rows only";
                        cmd.CommandText = strSql.ToString();
                        if (parameters != null && parameters.Count > 0)
                        {
                            foreach (var key in parameters.Keys)
                            {
                                SqlParameter parameter = new SqlParameter(key, parameters[key].ToString());
                                cmd.Parameters.Add(parameter);
                            }
                        }
                        SqlDataAdapter adapter = new SqlDataAdapter(cmd);
                        adapter.Fill(seldt);
                        cmd.Parameters.Clear();
                    }
                    catch (System.Data.SqlClient.SqlException ex)
                    {
                        throw new Exception(ex.Message);
                    }
                }
            }
            return seldt;
        }
        #endregion