ถ้าต้องการสร้าง Class ที่ใช้ Using ได้ต้องประกาศ class แบบไหนครับ

using System;

using (MyCalss myClass = new MyClass())
{
...
}

public static class clsDatabaseServices
    {

        public enum EnumConnectionType
        { ODBC, OLEDB, SqlClient }


        public static System.Data.DataTable GetTableForm(string _SQL, string strConn, EnumConnectionType ConnectionType)

        {
            System.Data.DataSet ds = new System.Data.DataSet();
            switch (ConnectionType)
            {
                case EnumConnectionType.ODBC:
                    System.Data.Odbc.OdbcConnection conn1 = new System.Data.Odbc.OdbcConnection(strConn);
                    conn1.Open();
                    System.Data.Odbc.OdbcDataAdapter adapter1 = new System.Data.Odbc.OdbcDataAdapter(_SQL, conn1);
                    adapter1.Fill(ds);
                    break;
                case EnumConnectionType.OLEDB:
                    System.Data.OleDb.OleDbConnection conn2 = new  System.Data.OleDb.OleDbConnection(strConn);
                    conn2.Open();
                    System.Data.OleDb.OleDbDataAdapter adapter2 = new  System.Data.OleDb.OleDbDataAdapter(_SQL, conn2);
                    adapter2.Fill(ds);
                    break;
                case EnumConnectionType.SqlClient:
                    System.Data.SqlClient.SqlConnection conn3 = new  System.Data.SqlClient.SqlConnection(strConn);
                    conn3.Open();
                    System.Data.SqlClient.SqlDataAdapter adapter3 = new  System.Data.SqlClient.SqlDataAdapter(_SQL, conn3);
                    adapter3.Fill(ds);

                    break;
            }

            return ds.Tables[0];

        }
        
       
    }

public static List<TORServices._DabaseSelected> ListContact_list()
        {
            List<TORServices._DabaseSelected> lst = new List<TORServices._DabaseSelected>();
            lst = TORServices.clsDatabaseServices.ReturnListIndex("SELECT * FROM  dbo.Contact_list", Properties.Settings.Default.BASEConnectionString, TORServices.clsDatabaseServices.EnumConnectionType.SqlClient);
            return lst;
        }

public static List<TORServices._DabaseSelected> ListContact_list()
        {
            List<TORServices._DabaseSelected> lst = new List<TORServices._DabaseSelected>();
            lst = TORServices.clsDatabaseServices.ReturnListIndex("SELECT * FROM  dbo.Contact_list", Properties.Settings.Default.BASEConnectionString, EnumConnectionType.SqlClient);
            return lst;
        }