Visual Studio 2005进行三层结构应用程序开发的简单实例

1.三层之间的关系：

三层是指：界面显示层(UI)，业务逻辑层(Business)，数据操作层(Data Access)

文字描述：

Clients对UI进行操作，UI调用Business进行相应的运算和处理，Business通过DataAccess对DataBase进行操作。

2.Data Access的具体实现：
DataAgent类型中变量和方法的说明：

private string m_strConnectionString; //连接字符串

private OleDbConnection m_objConnection; //数据库连接

public DataAgent(string strConnection) //构造方法，传入的参数为连接字符串

private void OpenDataBase() //打开数据库连接

private void #region CloseDataBase() //关闭数据库连接

public DataView GetDataView(string strSqlStat) //根据传入的连接字符串返回DataView

具体实现代码如下：

     public class DataAgent

     {

         #region Variables

         private string m_strConnectionString;

         private OleDbConnection m_objConnection;

         #endregion Variables

         #region Functions

         #region DataAgend

         /// <summary>

         /// Initial Function

         /// </summary>

         /// <param name="strConnection"></param>

         public DataAgent(string strConnection)

         {

              this.m_strConnectionString = strConnection;

         }

         #endregion DataAgend

         #region OpenDataBase

         /// <summary>

         /// function to open data base

         /// </summary>

         private void OpenDataBase()

         {

              try

              {

                   this.m_objConnection = new OleDbConnection();

                   this.m_objConnection.ConnectionString = this.m_strConnectionString;

                   if(this.m_objConnection.State != ConnectionState.Open)