单例模式

    class DBHelper

    {

        private static readonly string strConn = "Data Source=.;Integrated Security=true;Initial Catalog=myDB";

        private static SqlConnection sqlConn = null;

        private static DBHelper dbHelper = null;



        /// <summary>

        /// 数据库连接对象实例

        /// </summary>

        private DBHelper()

        {

            if (sqlConn == null)

            {

                sqlConn = new SqlConnection(strConn);

            }

        }



        /// <summary>

        /// 取得/创建对象实例

        /// </summary>

        /// <returns></returns>

        internal static DBHelper GetIntance()

        {

            if (dbHelper == null)

            {

                dbHelper = new DBHelper();

            }

            return dbHelper;

        }



        /// <summary>

        /// 打开数据库连接

        /// </summary>

        private void Open()

        {

            if (sqlConn.State == ConnectionState.Closed)

            {

                sqlConn.Open();

            }

        }



        /// <summary>

        /// 关闭数据库连接

        /// </summary>

        private void Close()

        {

            if (sqlConn.State == ConnectionState.Open)

            {

                sqlConn.Close();

            }

        }



        public int ExecuteSql(string strSql, SqlParameter[] para)

        {

            SqlCommand sqlCmd = new SqlCommand(strSql, sqlConn);

            if (para != null)

            {

                sqlCmd.Parameters.AddRange(para);

            }

            Open();

            int objResult = sqlCmd.ExecuteNonQuery();

            Close();

            return objResult;

        }



        public DataSet GetSqlDataSet(string strSql, SqlParameter[] para)

        {

            SqlCommand sqlCmd = new SqlCommand(strSql, sqlConn);

            if (para != null)

            {

                sqlCmd.Parameters.AddRange(para);

            }

            SqlDataAdapter sqlAdp = new SqlDataAdapter(sqlCmd);

            DataSet ds = new DataSet();

            sqlAdp.Fill(ds);

            return ds;

        }

    }

        //调用实例

        private static void GetDBList()

        {

            DBHelper dbHelper = DBHelper.GetIntance();

            DataSet ds = dbHelper.GetSqlDataSet("SELECT TOP 20 [StuId],[StuName] FROM [Student]", null);

            for (int i = 0; i < ds.Tables[0].Rows.Count; i++)

            {

                Console.WriteLine(ds.Tables[0].Rows[i][0].ToString() + ds.Tables[0].Rows[i][1].ToString());

            }

        }