本文主要是介绍vb.net三层实现登录例子，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
看三层已经很长时间了，中间有经过了期末考试、回家等等琐事，寒假开学的我已经回想不起什么事三层了，经过了三四天的重新复习，再加上查看各期师哥师姐的博客，终于，自己完成了C#视频中的登录小例子，下面就和大家分享一下先：
首先是界面：
这样感觉真心的好看
首先我们看一下实体层，也就是图片中的LoginModel
Public Class ModelDim _username As StringDim _password As StringDim _email As StringDim _score As IntegerPublic Property UserName As String '设置UserName属性GetReturn _usernameEnd GetSet(value As String)_username = valueEnd SetEnd PropertyPublic Property Password As String '设置Password属性GetReturn _passwordEnd GetSet(value As String)_password = valueEnd SetEnd PropertyPublic Property Email As StringGetReturn _emailEnd GetSet(value As String)_email = valueEnd SetEnd PropertyPublic Class UserDAOPublic conn As New SqlConnection("server=李卫中; database=Login;user id=sa;password=li")Public Function SelectUser(ByVal User As Model) As LoginModel.ModelDim reader As SqlDataReaderDim eUser As New LoginModel.ModelDim sql As String = "Select UserName,Password From Users Where UserName=@UserName And Password=@Password"Dim cmd As New SqlCommand(sql, conn) '创建sqlCommand对象cmd.CommandText = sql '获取SQL语句的具体内容cmd.CommandType = CommandType.Text '获取上述SQL语句的具体类型，在此为Selectcmd.Parameters.Add(New SqlParameter("@UserName", User.UserName)) '若用成eUser.UserName则会出现参数未传递的错误提示cmd.Parameters.Add(New SqlParameter("@Password", User.Password))conn.Open() '打开数据连接reader = cmd.ExecuteReader() '执行查询语句，并生成一个DataReader'读取查询到的数据，并返回给相应的属性While reader.Read()'获取数据库中相应字段的数据'数组必须从零开始读取，否则会超出其界限eUser.UserName = reader.GetString(0)eUser.Password = reader.GetString(1)End WhileReturn eUser '返回查询到的实体conn.Close()End FunctionPublic Class ScoresDAO '这里是实例中的那个登录见证，也就是Score那部分，其实我是照葫芦画瓢，照上面写的Public conn As New SqlConnection("server=李卫中; database=Login;user id=sa;password=li")Public Function UpdateScore(ByVal User As Model) As LoginModel.ModelDim eUser As New LoginModel.ModelDim sql As String = "INSERT INTO Scores (UserName,Score) values (@UserName,@Score)"Dim cmd As New SqlCommand(sql, conn) '创建sqlCommand对象cmd.CommandText = sql '获取SQL语句的具体内容cmd.CommandType = CommandType.Text '获取上述SQL语句的具体类型，在此为Selectcmd.Parameters.Add(New SqlParameter("@UserName", User.UserName))cmd.Parameters.Add(New SqlParameter("@Score", 10))conn.Open()cmd.ExecuteNonQuery()Return eUser '返回查询到的实体conn.Close() '视频里讲过，用完了之后，最好是断开连接，省的占用通道 '关闭连接End FunctionEnd ClassU层：界面层
Public Class frmLoginPrivate Sub frmLogin_Load(sender As Object, e As EventArgs) Handles MyBase.LoadtxtUserName.Focus()txtUserName.MaxLength = 11 '设置txtUserName 属性txtPassword.MaxLength = 10End SubPrivate Sub btnLogin_Click(sender As Object, e As EventArgs) Handles btnLogin.ClickTryDim euser2 As New LoginModel.Model '实例化新的UserInfo，用来传递B层的实体Dim euser3 As LoginModel.Model '定义一个类型为UserInfo的参数，用来赋值'用户名、密码传入实体层euser2.UserName = Trim(txtUserName.Text)euser2.Password = txtPassword.TextDim mgr As New LoginBLL.LoginManagereuser3 = mgr.UserLogin(euser2)Catch ex As ExceptionMessageBox.Show(ex.Message.ToString())End TryEnd SubPrivate Sub btnCancel_Click(sender As Object, e As EventArgs) Handles btnCancel.ClickMe.Close()End Sub
End ClassPublic Function UserLogin(ByVal User As LoginModel.Model) As LoginModel.ModelDim uDao As New LoginDAL.UserDAODim sDao As New LoginDAL.ScoresDAODim eUser1 As LoginModel.ModeleUser1 = uDao.SelectUser(User)If IsNothing(eUser1.UserName) ThenThrow New Exception("密码错误或用户名不存在，登录失败")ElseeUser1 = sDao.UpdateScore(User)Return eUser1End IfEnd Function
自己编点，看看师哥师姐们的博客，结合一下自己以前学到的知识，要知道，所谓的三层其实就是一个解耦的过程，和我们后面遇到的“七层”是一样，用心看看，应该不难
从上面可以看出，我用到的是传实体，之前我问过师傅，到底是传实体好呢，还是传参好呢？（各有各的好处，不同的地方、不同的情况用不同的发放）这是师傅对我说的，虽然我还不能完全掌握使用方法的能力，但是通过练习，我没问题
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