關于三層，看完一遍，想著開始敲七層，看著別人的代碼敲都有點找不到，于是重新敲了一遍三層，收獲很多！
首先，它沒有模板，也不是一下子就完成的，它是有思路的，根據思路走，整個過程就是很自然而然的過程！

DAL

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data;
using System.Data.SqlClient;namespace Login.DAL
{public class UserDAO//和用戶數據庫做對比{public Login.Model.UserInfo  SelectUser(string userName,string password)//告訴用戶存在不存在，存在就返回，不存在就拋出異常{//用到數據模型using (SqlConnection conn = new SqlConnection(DBUtil.ConnString)){SqlCommand cmd = conn.CreateCommand();cmd.CommandText = @"SELECT ID ,Password,Email from Users where UserName=@UserName and Password=@Password";cmd.CommandType = CommandType.Text;cmd.Parameters.Add(new SqlParameter("@UserName", userName));cmd.Parameters.Add(new SqlParameter("@Password", password));conn.Open();SqlDataReader reader = cmd.ExecuteReader();Login.Model.UserInfo user = null;while (reader.Read())  //reader.Read()為真，正確執行查詢{if(user==null)    //一開始設置為空，為了實例出UserInfo類{user = new Login.Model.UserInfo();}user.ID = reader.GetInt32(0);//從數據庫中讀取的結果賦值數據模型user.UserName = reader.GetString(1);user.Password = reader.GetString(2);if(!reader.IsDBNull(3)){user.Email = reader.GetString(3);}}return user;}//throw new NotImplementedException();//在無法實現請求的操作和方法時的操作}}
}

BLL

UserDAＯ

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;namespace Login.BLL
{public class LoginManager{public Login.Model.UserInfo  Login(string userName,string password){Login.DAL.UserDAO uDAO = new DAL.UserDAO();Login.Model.UserInfo user = uDAO.SelectUser(userName, password);if(user!=null){Login.DAL.ScoreDAO sDAO = new Login.DAL.ScoreDAO();sDAO.UpdateScore(userName, 10);return user;}else{throw new Exception("登錄失敗");}}}
}

ScoreDAO

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data;
using System.Data.SqlClient;namespace Login.DAL //data access level      DAO data access Object
{public class ScoreDAO//登錄積分處理{public void UpdateScore(string userName,int value){using (SqlConnection conn = new SqlConnection(DBUtil.ConnString)){SqlCommand cmd = conn.CreateCommand();cmd.CommandText = @"INSERT INTO SCORES(UserName,Score) Value(@UserName,@Score)";cmd.CommandType = CommandType.Text;cmd.Parameters.Add(new SqlParameter("@UserName", userName));cmd.Parameters.Add(new SqlParameter("@Score", value));conn.Open();cmd.ExecuteNonQuery();}}}
}

DBUtil

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;namespace Login.DAL
{class DBUtil{public static string ConnString = @"Server=Rancho; Database=Login; Uid=sa; Password=123456 ";}
}

Model

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;namespace Login.Model
{public class UserInfo{private int iD;private string userName;private string password;private string email;public int ID { get => iD; set => iD = value; }public string UserName { get => userName; set => userName = value; }public string Password { get => password; set => password = value; }public string Email { get => email; set => email = value; }}
}

UI層

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.SqlClient;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;namespace LoginUI
{public partial class Form1 : Form{public Form1(){InitializeComponent();}private void butLogin_Click(object sender, EventArgs e){//IDbConnection conn = new SqlConnection("....");//IDbCommand cmd = conn.CreateCommand();//cmd.CommandText = "Select UserName From UserTable where";//cmd.ExecuteReader();string userName = txtUserName.Text.Trim();string password = txtPassWord.Text;Login.BLL.LoginManager mgr = new Login.BLL.LoginManager();Login.Model .UserInfo user=mgr.Login(userName ,password );MessageBox.Show("登錄用戶：" + userName);}}
}

總結

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