三层架构源代码

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using Model;
using BLL;

namespace UI
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        private UserService us = new UserService();
        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void button1_Click(object sender, EventArgs e)
        {
            User user = new User();
            user.UserName = txtUserName.Text.Trim();
            user.Password = txtPassword.Text.Trim();
            if (us.CheckUser(user))
            {
                MessageBox.Show("登录成功!");           //UI层
            }
            else
            {
                MessageBox.Show("登录失败!");
            }
        }


using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Model;
using DAL;

namespace BLL
{
    public class UserService
    {
        private UserDAO dao = new UserDAO();
        public bool CheckUser(User user)
        {
            User u = dao.GetUserByUserName(user.UserName);
            if (u == null)
            {
                return false;
            }
            else                              //bll层
            {
                return user.Password == u.Password;
            }
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Model;
using System.Data;
using System.Data.SqlClient;

namespace DAL
{
    public class UserDAO
    {
       
        public User GetUserByUserName(string username)
        {
            string sql = "select * from users where username=@username";
            List<SqlParameter> paras=new List<SqlParameter>();
            paras.Add(new SqlParameter("@username",username));
            DataTable  dt= SqlHelper.ExecuteTable(sql,paras);           
            User user = null;
            if (dt.Rows.Count == 1)
            {                                              //dal层
                user = new User();
                DataRow row = dt.Rows[0];
                user.UserId = Convert.ToInt32(row[0]);
                user.UserName = row[1].ToString();
                user.Password = row[2].ToString();
            }
            return user;
            
        }
    }
}
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Model
{
    public class User                              //实体层
    {
        public int UserId { get; set; }
        public string UserName { get; set; }
        public string Password { get; set; }
    }
}


<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
    </startup>
  <connectionStrings>
    <add name="ConnStr" connectionString="server=.;database=schooldb;uid=sa;pwd=123"/>
  </connectionStrings>
</configuration>

添加引用 程序集  configuration 
privarte static readonly string 名字=configrationmanager