补充：MyMeans类

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Data;using System.Data.SqlClient;using System.Windows.Forms;namespace PWMS_SYSTEM_V1._0.DataClass{    class MyMeans    {        #region the property        public static string LogIn_ID = "";        public static string LogIn_Name = "";        public static string Mean_Table = "", Mean_SQL = "", Mean_Field = "";        public static SqlConnection My_Con;        public static string M_str_sqlcon = "Server=DESKTOP-AIE7LD0\\NAME;Database=db_PWMS;Integrated Security=true";        public static int LogIn_n = 0;        public static string AllSql = "Select * from tb_Stuffbusic";        #endregion        //建立与数据库的连接，并打开，返回sqlconnection的对象信息        public static SqlConnection getcon()        {            My_Con = new SqlConnection(M_str_sqlcon);            My_Con.Open();            return My_Con;        }        //测试打开数据库        public void con_open()        {            getcon();            //con_close();        }        //如果这个连接状态为连接时，则关闭数据库连接，释放所有空间        public void con_close()        {            if (My_Con.State == ConnectionState.Open)            {                My_Con.Close();                My_Con.Dispose();            }        }        //利用sqldatareader来对数据进行只读        public SqlDataReader getCommand(string SQLstring)        {            getcon();            SqlCommand My_Command = My_Con.CreateCommand();            My_Command.CommandText = SQLstring;            SqlDataReader My_reader = My_Command.ExecuteReader();            return My_reader;        }        //利用ExecuteNonQuery来进行对数据的添加修改和删除等操作        public void GetA_M_D_command(string A_M_Dstring)        {            getcon();            SqlCommand SQLcommand = new SqlCommand(A_M_Dstring, My_Con);            SQLcommand.ExecuteNonQuery();            SQLcommand.Dispose();            con_close();                        }        //执行数据库中的添加修改和删除操作，使用dataset现象        public DataSet GetDataSet(string sqlStr, string tableName)        {            getcon();            SqlDataAdapter sqlDataAdappter = new SqlDataAdapter(sqlStr, My_Con);            DataSet My_DataSet = new DataSet();            sqlDataAdappter.Fill(My_DataSet, tableName);            con_close();            return My_DataSet;        }    }    }