三层已经学了一些时间了，開始认为自己能够用C#敲代码了，就用C#写了一个实现登陆的，真正再用在机房中，还是认为非常吃力的，所以，决定用vb.net敲了。以下是我用vb.net实现的登陆，能够给大家做一些參考。
这是构架的三层
数据库中的表T_User_DAL：UserI，Level，Password，Head，computer
首先看一下
Entity层：
Public Class UserInfoEntity#Region "定义变量" Private _userID As String Private _level As String Private _Head As String Private _password As String#End Region Public Property UserID() As String '将T_User_DAL表中的每个实体都传上去，实体是依据表来建的，不是功能 Get Return _userID End Get Set(value As String) _userID = value End Set End Property Public Property Level() As String Get Return _level End Get Set(ByVal value As String) _level = value End Set End Property Public Property Head() As String Get Return _Head End Get Set(value As String) _Head = value End Set End Property Public Property Password() As String Get Return _password End Get Set(value As String) _password = value End Set End PropertyEnd Class
DAL层：
为了可以减少耦合一定要将连接字符串拿出来，不要每个DAL中都写一边。
Imports System.DataImports System.Data.SqlClientPublic Class SqlUtil Public Shared Function connstring() As String 'connstring = "Server=192.168.24.183;Database=ReconsitutionCharge_sys;User ID=sa;Password=123456" ‘会出现无法识别userid的错误 connstring = "Server=mx; Database=ReconsitutionCharge_sys; User ID=sa; Password=123456" '连接SQL的字符串 End FunctionEnd Class
T_User_dal表DAL层代码：
Imports System.Data.SqlClientImports System.DataPublic Class UserDAL Public Function SelectUser(ByVal user As Entity.UserInfoEntity) As Entity.UserInfoEntity Dim conn As New SqlConnection '定义连接打开数据库 Dim cmd As New SqlCommand '定义数据库命令 conn = New SqlConnection(SqlUtil.connstring()) '实例化SQLUntil中返回的字符串 cmd.Connection = conn cmd.CommandText = "Select * From T_User_DAL Where UserID=@UserID and Password=@Password" '存储过程 cmd.Parameters.Add(New SqlParameter("@UserID", user.UserID)) '赋值，传參 cmd.Parameters.Add(New SqlParameter("@Password", user.Password)) cmd.CommandType = CommandType.Text 'CommandText 属性设置为存储过程的名称。当调用 Execute 方法之中的一个时，该命令将运行此存储过程 conn.Open() '打开连接 Dim reader As SqlClient.SqlDataReader '读取数据库中的表 reader = cmd.ExecuteReader() Dim users As New Entity.UserInfoEntity '实例化实体 While (reader.Read()) 'If users Is Nothing Then ' user = New Entity.UserInfoEntity 'End If users.UserID = reader.GetString(reader.GetOrdinal("UserID")) users.Password = reader.GetString(reader.GetOrdinal("Password")) End While conn.Close() Return users End FunctionEnd Class
BLL层：
Public Class LoginBLL Function UserLogin(ByVal user As Entity.UserInfoEntity) As Entity.UserInfoEntity Dim uDAL As New DAL.UserDAL '实例化了DAL中的UserDAL Dim users As New Entity.UserInfoEntity '实例化了Entity层信息表 users = uDAL.SelectUser(user) 'selectUser是返回一个Entity类的，给它赋值user Return users '返回users实体 End FunctionEnd Class
UI层：
界面设计：
Private Sub btnLogin_Click(sender As Object, e As EventArgs) Handles btnLogin.Click Dim mgr As New BLL.LoginBLL '实例业务层 Dim user As New Entity.UserInfoEntity '实例实体 Dim users As Entity.UserInfoEntity '接收实体，用于接收UserLogin（）返回的数据类型，假设没有New就不是实例化 user.UserID = txtUserID.Text.Trim() '给实体层传入值 user.Password = TxtPassword.Text.Trim() If txtUserID.Text = "" Then '推断输入是否正确 MsgBox("username不能为空！") Return End If If TxtPassword.Text = "" Then MsgBox("password不能为空！") Return End If Try 'users接收实体 users = mgr.UserLogin(user) If (users.UserID Is Nothing And users.Password Is Nothing) Then '假设users不为空，则登陆成功！ MsgBox("登陆失败，username和password不匹配") Return Else MsgBox("登陆成功！登陆用户：" + user.UserID) End If Catch ex As Exception MsgBox(ex.Message()) End Try End SubEnd Class