上篇文章讲到三层。接下来就通过一个实例详细的看怎么用三层实现用户登陆界面。

一、Model实体（LoginModel）:

namespace LoginModel
{//加入类:UserInfo  Model实体作用：封装数据，使数据在三层中传输 。更倾向于业务逻辑层public class UserInfo{//定义用户属性public int ID { get; set; }public string UserName { get; set; }public string Password { get; set; }}
}

二、UI层的设计：

首先简单的界面相信大家都会：

接下来是代码：

namespace LoginUI
{public partial class frmLogin : Form{public frmLogin(){InitializeComponent();}private void btnLogin_Click(object sender, EventArgs e){//UI层将用户输入数据传递给BLL层string userName = txtUserName.Text.Trim();string password = txtPassword.Text;LoginBLL.LoginManager mgr = new LoginBLL.LoginManager();LoginModel.UserInfo user = mgr.UserLogin(userName, password);//将UI层返回业务层传递的数据给用户MessageBox.Show("登陆用户：" + user.UserName);}       }
}

三、BLL层代码

namespace LoginBLL
{public class LoginManager{public LoginModel.UserInfo UserLogin(string userName, string password){LoginDAL.UserDAO uDao = new LoginDAL.UserDAO();//实例化DAL层LoginModel.UserInfo user = uDao.SelectUser(userName, password);//不需訪问数据源直接运行业务逻辑if (user != null){return user;}else{throw new Exception("登陆失败");                }}}
}

四、DAL层  代码

 public class UserDAO{public LoginModel.UserInfo SelectUser(string userName, string Password){//建立数据库连接string ConnString = @"Server=192.168.24.154;DataBase=机房收费系统人员记录; User ID=sa; Password=123";using (SqlConnection conn = new SqlConnection(ConnString)){//运行SQL语句进行查询SqlCommand cmd = conn.CreateCommand();cmd.CommandText = @"SELECT ID,UserName,Password FROM UserInfo WHERE UserName=@UserName AND Password=@Password";//输出查询结果cmd.CommandType = CommandType.Text;//加入两个參数cmd.Parameters.Add(new SqlParameter(@"UserName", userName));cmd.Parameters.Add(new SqlParameter(@"Password", Password));conn.Open();SqlDataReader reader = cmd.ExecuteReader();LoginModel.UserInfo user = null;//读取详细的数据while (reader.Read()){if (user == null){user = new LoginModel.UserInfo();}//读取查询到的数据user.ID = reader.GetInt32(0);user.UserName = reader.GetString(1);user.Password = reader.GetString(2);}return user;}}}
}

登陆：

结果显示：