怎么实现。NET三层架构（要例子）

Asp.net三层结构入门示例源码{比较适合初学的朋友}http://www.51aspx.com/CV/AspNet_sancengjiegou/

可以看petshop的分解~~
刚开始接触看petshop3就够用了~~
你可以下载微软苏鹏讲的petshop 与 n层架构~~可以在csdn上下载：最新三层构架网站 OA设计4大示例

petshop用接口,应该是叫工厂反射吧

MVC 三层结构－－－－－－－－－－－－－－－－－－－－－Model－－－－－－－－－－－
using System;
using System.Collections.Generic;
using System.Text;namespace Model
{
    public class guestbook //留言本实体类
    {
        private string _id, _name, _ip, _content, _email, _pic, _recontent;
        DateTime _time;        #region 设置属性
        //id
        public string Id
        {
            get { return _id; }
            set { _id = value; }
        }
        //网名
        public string Name
        {
            get { return _name; }
            set { _name = value; }
        }        //时间
        public DateTime  Time
        {
            get { return _time; }
            set { _time = value; }
        }        //IP地址
        public string Ip
        {
            get { return _ip; }
            set { _ip = value; }
        }        //留言内容
        public string Content
        {
            get { return _content; }
            set { _content = value; }
        }        //电子信箱
        public string Email
        {
            get { return _email; }
            set { _email = value; }
        }        //头像
        public string Pic
        {
            get { return _pic; }
            set { _pic = value; }
        }        //回复内容
        public string Recontent
        {
            get { return _recontent; }
            set { _recontent = value; }
        }
        #endregion    }
}
－－－－－－－－－－－－－－－－－－－－－－接口IDAL－－－－－－－－－－－－－－－－－－－－－－

DAL  ----1 FILE
----------------------------
using System;
using System.Collections.Generic;
using System.Text;
using System.Configuration ;
using System.Collections;
using System.Xml;
using System.Xml.XPath;
using IDAL;
using Model;namespace DAL
{
    class xml:Iguestbook
    {
        string xmlGuestBookPath = System.Web.HttpContext.Current.Server.MapPath("../App_Data/") + ConfigurationSettings.AppSettings["xmlConnectionString"];
        //得到所有留言
        public  guestbook[] getListGuestBook()
        {
            XmlDataDocument xmlDoc = new XmlDataDocument();
            xmlDoc.Load(xmlGuestBookPath);//打开留言本xml文档
            XmlNodeList xnl = xmlDoc.SelectSingleNode("guestBooks").ChildNodes;//读取所有结点
            XmlElement xe ;//声明一个元素
            ArrayList guest = new ArrayList();
            foreach (XmlNode xn in xnl)
            {
                guestbook gb = new guestbook();
                xe = (XmlElement)xn;//转换这个节点为一个元素
                gb.Time = DateTime.Parse(xe.GetAttribute("time"));//得到留言时间
                XmlNodeList xnlChild = xn.ChildNodes ;
                gb.Id = gb.Time.ToString();//以时间为主键
                gb.Name = xn.ChildNodes[0].InnerText;
                gb.Ip = xn.ChildNodes[1].InnerText;
                gb.Content = xn.ChildNodes[2].InnerText;
                gb.Recontent = xn.ChildNodes[3].InnerText;
                gb.Pic = xn.ChildNodes[4].InnerText;
                gb.Email = xn.ChildNodes[5].InnerText;
                guest.Add(gb);
            }
            guest.Reverse();//数组反转，最后一条留言在第一位显示
            return (guestbook[])guest.ToArray(typeof(guestbook));
        }
            //得到一条留言
        public  guestbook[] getOnly(string id)
        {

            guestbook  gb = new guestbook();
            ArrayList guest = new ArrayList();
            XmlDataDocument xmlDoc = new XmlDataDocument();
            xmlDoc.Load(xmlGuestBookPath);
            XmlNodeList xnl = xmlDoc.SelectSingleNode("guestBooks").ChildNodes;
            XmlElement xe;
            foreach (XmlNode xn in xnl)
            {
                xe = (XmlElement)xn;
                gb.Time  = DateTime.Parse (xe.GetAttribute("time"));
                gb.Id = gb.Time.ToString();//以时间为主键
                if (xe.GetAttribute("time") == id)
                {
                    XmlNodeList xnlChild = xn.ChildNodes;
                    gb.Name = xn.ChildNodes[0].InnerText;
                    gb.Ip = xn.ChildNodes[1].InnerText;
                    gb.Content = xn.ChildNodes[2].InnerText;
                    gb.Recontent = xn.ChildNodes[3].InnerText;
                    gb.Pic = xn.ChildNodes[4].InnerText;
                    gb.Email = xn.ChildNodes[5].InnerText;
                    guest.Add(gb);
                }
            }
            return (guestbook[])guest.ToArray(typeof(guestbook));
        }        //添加留言内容
        public void setGuestBook(guestbook gb)
        {
            XmlDataDocument xmlDoc = new XmlDataDocument();
            xmlDoc.Load(this.xmlGuestBookPath);
            //选择根结点
            XmlNode root = xmlDoc.SelectSingleNode("guestBooks");
            XmlElement xe = xmlDoc.CreateElement("guestBook");//添加一个新结点元素
            xe.SetAttribute("time", gb.Time.ToString());//添加元素属性
            gb.Id = gb.Time.ToString();//以时间为关键字段            XmlElement xesub1 = xmlDoc.CreateElement("name");//创建子无素name
            xesub1.InnerText = gb.Name;
            xe.AppendChild(xesub1);//添加到xe结点中            XmlElement xesub2 = xmlDoc.CreateElement("ip");
            xesub2.InnerText = gb.Ip;
            xe.AppendChild(xesub2);            XmlElement xesub3 = xmlDoc.CreateElement("content");
            xesub3.InnerText = gb.Content;
            xe.AppendChild(xesub3);            XmlElement xesub4 = xmlDoc.CreateElement("recontent");
            xesub4.InnerText = gb.Recontent;
            xe.AppendChild(xesub4);            XmlElement xesub5 = xmlDoc.CreateElement("pic");
            xesub5.InnerText = gb.Pic;
            xe.AppendChild(xesub5);            XmlElement xesub6 = xmlDoc.CreateElement("email");
            xesub6.InnerText = gb.Email;
            xe.AppendChild(xesub6);            root.AppendChild(xe);//新建节点添加到根结点中            xmlDoc.Save(this.xmlGuestBookPath);//保存        }        //回复留言
        public void setReGuestBook(guestbook Regb)
        {
            XmlDocument xmlDoc = new XmlDocument();
            xmlDoc.Load(this.xmlGuestBookPath);
            XmlNodeList xnl = xmlDoc.SelectSingleNode("guestBooks").ChildNodes;
            foreach (XmlNode xn in xnl)
            {
                XmlElement xe = (XmlElement)xn;
                if (xe.GetAttribute("time") == Regb.Id)
                {
                    xe.ChildNodes[3].InnerText = Regb.Recontent;//添加回复内容
                }
            }
            xmlDoc.Save(this.xmlGuestBookPath);
        }        //删除留言
        public bool delGuestBook(string time)
        {
            XmlDataDocument xmlDoc = new XmlDataDocument();
            xmlDoc.Load(this.xmlGuestBookPath);
            XmlNodeList  xnl = xmlDoc.SelectSingleNode("guestBooks").ChildNodes ;
            XmlNode xnroot = xmlDoc.SelectSingleNode("guestBooks");//查找根结点，为删除子结点做准备
            foreach (XmlNode xn in xnl)//循环所有子结点
            {
                XmlElement xe = (XmlElement)xn;
                if (xe.GetAttribute("time") == time) //对比是否是要删除的结点
                {
                    xnroot.RemoveChild(xe);//从根结点删除
                    xmlDoc.Save(this.xmlGuestBookPath);
                    return true;
                }
            }
            return false;
        }
    }
}DAL ----- 2----FILE
--------------------------------------------
using System;
using System.Collections.Generic;
using System.Text;
using System.Data.SqlClient;
using System.Configuration;
using System.Collections;
using IDAL;
using Model;namespace DAL
{
    class Sql : Iguestbook
    {
        private string connectionString = System.Configuration.ConfigurationSettings.AppSettings["sqlConnectionString"] + System.Web.HttpContext.Current.Server.MapPath("../App_Data/myPage.mdf");
        /// <summary>
        /// 读取数据库中所有留言
        /// </summary>
        /// <returns>返回guestbool数组</returns>
        public guestbook[] getListGuestBook()
        {
            using (SqlConnection Conn = new SqlConnection(connectionString))
            {
                SqlCommand Cmd = new SqlCommand("select * from guestbook order by id desc",Conn);
                Conn.Open();                ArrayList guest = new ArrayList();
                SqlDataReader Ddr = Cmd.ExecuteReader();
                while (Ddr.Read())
                {
                    guestbook gb = new guestbook();
                    gb.Id = Ddr["id"].ToString();
                    gb.Name =Ddr["name"].ToString();
                    gb.Time = DateTime.Parse(Ddr["times"].ToString());
                    gb.Ip = Ddr["ip"].ToString();
                    gb.Content = Ddr["content"].ToString();
                    gb.Recontent =Ddr["recontent"].ToString();
                    gb.Pic = Ddr["pic"].ToString();
                    gb.Email = Ddr["email"].ToString();
                    guest.Add(gb);
                }
                Ddr.Close();                return (guestbook[])guest.ToArray(typeof(guestbook));
            }        }

--------BLL------------------------------
using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Reflection;//反射命名空间
using DAL;
using IDAL;
/// <summary>
/// 工厂类
/// </summary>
public class DriveGuestbook
{
public DriveGuestbook()
{
//
// TODO: 在此处添加构造函数逻辑
// }    public Iguestbook drive()
    {
        string assemblyName = ConfigurationManager.AppSettings["assembly"];//获取程序集名称        string constructor = ConfigurationManager.AppSettings["constructor"];//获取默认构造器名称        return  (Iguestbook)Assembly.Load(assemblyName).CreateInstance(constructor, false);
        //return (Iguestbook)Assembly.Load("DAL").CreateInstance("DAL.Sql", false);
    }    public void driver()
    {
      //(Iblog)Assembly.Load("DAL .DataSet1TableAdapters ").CreateInstance("DAL .DataSet1TableAdapters .blogNoteTableAdapter", false);
    }}
-------------------
using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using Model;
using IDAL;
/// <summary>
/// guestbook中间业务层
/// </summary>public class InterGuestbook //: Iguestbook
{
public InterGuestbook()
{
//
// TODO: 在此处添加构造函数逻辑
//
}    //得到留言列表内容
    public guestbook []  getListGuestBook()
    {
         // (new DriveGuestbook()).drive().getListGuestBook();
        //          反射类            相应驱动       接口方法
        return (new DriveGuestbook()).drive().getListGuestBook();//通过接口调用数据访问层
    }    //得到一条留言
    public guestbook [] only(string id)
    {
        return  (new DriveGuestbook()).drive().getOnly(id);
    }    //添加留言内容
    public  void setGuestBook(string name,string email,string content,string pic)
    {        guestbook gb = new guestbook();
        if (name  == string.Empty)
        {
            gb.Name = "匿名";
        }
        else
        {
            gb.Name = ReplaceString.Replace(name);
        }
        if (email  == string.Empty)
        {
            gb.Email = "无";
        }
        else
        {
            gb.Email = email ;
        }
        gb.Content = ReplaceString.Replace(content);
        gb.Ip = System.Web.HttpContext.Current.Request.UserHostAddress.ToString();
        gb.Pic = "../App_Themes/Default/images/" + face(pic);
        gb.Time = DateTime.Now;
        (new DriveGuestbook()).drive().setGuestBook(gb);
    }    /// <summary>
    /// 留言头像
    /// </summary>
    /// <param name="pic"></param>
    /// <returns></returns>
    private string face(string pic)
    {
        switch (pic)
        {
            case "face1": return "1.gif";
            case "face2": return "2.gif";
            case "face3": return "3.gif";
            case "face4": return "4.gif";
            case "face5": return "5.gif";
        }
        return "1.gif";
    }    //回复留言
    public  void setReGuestBook(string content,string id)
    {
        guestbook gb = new guestbook();
        gb.Recontent ="<hr /><font color='#FF0000'>管理员回复:</font>"+ReplaceString.Replace(content);
        gb.Id = id;
        (new DriveGuestbook()).drive().setReGuestBook(gb);
    }    //删除留言
    public bool delGuestBook(string id)
    {
        return (new DriveGuestbook ()).drive ().delGuestBook (id);
    }
}

用VS.NET进行三层结构应用程序的开发一、三层之间的关系：
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Data Access对Data Base进行操作。优点：
1、增加了代码的重用。Data Access可在多个项目中公用；Business可在同一项目的不同地方使用（如某个软件B/S和C/S部分可以共用一系列的Business组件）。
2、使得软件的分层更加明晰，便于开发和维护。美工人员可以很方便地设计UI设计，并在其中调用Business给出的接口，而程序开发人员则可以专注的进行代码的编写和功能的实现。

二、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)
{
this.m_objConnection.Open();
}
}
catch(Exception e)
{
throw e;
}
}
#endregion OpenDataBase #region CloseDataBase
/// <summary>
/// the function to cloase data base
/// </summary>
private void CloseDataBase()
{
if(this.m_objConnection != null)
{
if(this.m_objConnection.State == ConnectionState.Open)
{
this.m_objConnection.Close();
}
}
}
#endregion #region GetDataView
/// <summary>
/// Execute the sql and return the default table view
/// </summary>
/// <param name="strSelectString">Select String</param>
/// <returns>DataView of the DataTable</returns>
public DataView GetDataView(string strSqlStat)
{
try
{
this.OpenDataBase();
OleDbDataAdapter objDataAdapter = new OleDbDataAdapter(strSqlStat.Trim(),this.m_objConnection);
DataSet objDataSet = new DataSet();
objDataAdapter.Fill(objDataSet);
return objDataSet.Tables[0].DefaultView;
}
catch(Exception e)
{
throw e;
}
finally
{
this.CloseDataBase();
}
}
#endregion GetDataTable
#endregion Functions }

三、Business的具体实现：
建立名为Base的类，此类作为其他事务类的基类，其中定义了一个DataAgent的实例。其他所有的Business类都从该改类派生。
在该类中添加对DataAgent的引用，使所有的事务类都能使用DataAgent中的方法。Base.cs源代码： public abstract class Base
{
#region DataAgent
private DataAgent m_objDBAgent; protected DataAgent OleDBAgent
{
get
{
if(this.m_objDBAgent == null)
{
this.m_objDBAgent = this.CreateAgent();
}
return this.m_objDBAgent;
}
set
{
this.m_objDBAgent = value;
}
}
#endregion DataAgent public Base()
{
} #region CreateAgent
/// <summary>
/// Create a new DataAgent
/// </summary>
/// <returns>the DataAgent</returns>
private DataAgent CreateAgent()
{
string strConnection = ConfigurationSettings.AppSettings["ConnectionString"];
return new DataAgent(strConnection);
}
#endregion CreateAgent
}
准备好了数据操作层和事务层的基类，底下就可以正式地开始业务逻辑类的开发了，如有一个显示新闻的类News,其中包含了一个GetNewsLsit()的方法，该方法用来获取所有的新闻标题列表，代码如下： public class News: Base
{
public News Contact()
{ } public DataView GetNewsList()
{
string strSql;
strSql = "";
strSql += "   SELECT Top 10 NewsId,NewsTitle ";
strSql += "     FROM Tb_News";
strSql += "    WHERE NewsEnable = 1";
strSql += " ORDER BY NewsId "; return base.OleDBAgent.GetDataView(strSql); }
}由于数据库结构比较简单，在此就不再给出详细的表结构。四、UI层对Business中接口的调用
首先，在页面中添加对News类的引用。
然后，在页面中添加一个(DataGrid)dgNews用来显示新闻列表。
在Page Behind的Page_Load方法中添加如下代码： News objNews = new News();
this.dgNews.DataSource = objNews.GetNewsList();
this.dgNews.DataBind(); 至此，大功告成！

Petshop 4.0下载地址，好好研究吧，能学会三层架构，还能学、到不少别的东西。
http://download.microsoft.com/download/8/0/1/801ff297-aea6-46b9-8e11-810df5df1032/Microsoft%20.NET%20Pet%20Shop%204.0.msi

NickLee.Fortune
www.cnblogs.com/mail-ricklee

调试易

怎么实现。NET三层架构（要例子）

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