三層已經學了一些時間了，開始認為自己能夠用C#敲代碼了，就用C#寫了一個實現登陸的，真正再用在機房中。還是認為非常吃力的，所以。決定用vb.net敲了。以下是我用vb.net實現的登陸。能夠給大家做一些參考。

這是構架的三層

數據庫中的表T_User_DAL：UserI。Level，Password，Head，computer

首先看一下

Entity層：

Public Class UserInfoEntity
#Region "定義變量"
    Private _userID As String
    Private _level As String
    Private _Head As String
    Private _password As String
#End Region
    Public Property UserID() As String            ‘將T_User_DAL表中的每個實體都傳上去，實體是依據表來建的，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 Property


End Class

DAL層：

為了可以減少耦合一定要將連接字符串拿出來。不要每個DAL中都寫一邊。

Imports System.Data
Imports System.Data.SqlClient
Public Class SqlUtil
    Public Shared Function connstring() As String
        ‘connstring = "Server=192.168.24.183;Database=ReconsitutionCharge_sys;User ID=sa;Password=123456"     ‘會出現無法識別userid的錯誤
        connstring = "Server=mx; Database=ReconsitutionCharge_sys; User ID=sa; Password=123456"         ‘連接SQL的字符串
    End Function

End Class

T_User_dal表DAL層代碼：

Imports System.Data.SqlClient
Imports System.Data
Public Class UserDAL
    Public Function SelectUser(ByVal user As Entity.UserInfoEntity) As Entity.UserInfoEntity
        Dim conn As New SqlConnection                          ‘定義連接打開數據庫
        Dim cmd As New SqlCommand                              ‘定義數據庫命令
        conn = New SqlConnection(SqlUtil.connstring())         ‘實例化SQLUntil中返回的字符串 
        cmd.Connection = conn


        cmd.CommandText = "Select * From T_User_DAL Where [email protected] and [email protected]"        ‘存儲過程


        cmd.Parameters.Add(New SqlParameter("@UserID", user.UserID))                        ‘賦值，傳參
        cmd.Parameters.Add(New SqlParameter("@Password", user.Password))
        cmd.CommandType = CommandType.Text                                                  ‘CommandText 屬性設置為存儲過程的名稱。當調用 Execute 方法之中的一個時，該命令將運行此存儲過程
        conn.Open()                                                                         ‘打開連接




        Dim reader As SqlClient.SqlDataReader                                               ‘讀取數據庫中的表
        reader = cmd.ExecuteReader()


        Dim users As New Entity.UserInfoEntity                                              ‘實例化實體


        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 Function
End Class

BLL層：

Public Class LoginBLL
    Function UserLogin(ByVal user As Entity.UserInfoEntity) As Entity.UserInfoEntity
        Dim uDAL As New DAL.UserDAL                                 ‘實例化了DAL中的UserDAL
        Dim users As New Entity.UserInfoEntity                      ‘實例化了Entity層信息表

        users = uDAL.SelectUser(user)                               ‘selectUser是返回一個Entity類的，給它賦值user
        Return users                                                ‘返回users實體
    End Function

End Class

UI層：

界面設計：

   Private Sub btnLogin_Click(sender As Object, e As EventArgs) Handles btnLogin.Click
        Dim mgr As New BLL.LoginBLL             ‘實例業務層
        Dim user As New Entity.UserInfoEntity   ‘實例實體
        Dim users As Entity.UserInfoEntity      ‘接收實體，用於接收UserLogin（）返回的數據類型，假設沒有New就不是實例化


        user.UserID = txtUserID.Text.Trim()     ‘給實體層傳入值
        user.Password = TxtPassword.Text.Trim()
        If txtUserID.Text = "" Then             ‘推斷輸入是否正確
            MsgBox("username不能為空！")
            Return
        End If

        If TxtPassword.Text = "" Then
            MsgBox("password不能為空！")
            Return
        End If

        Try                                    ‘users接收實體
            users = mgr.UserLogin(user)

            If (users.UserID Is Nothing And users.Password Is Nothing) Then      ‘假設users不為空。則登陸成功！
                MsgBox("登陸失敗，username和password不匹配")
                Return
            Else
                MsgBox("登陸成功。登陸用戶：" + user.UserID)
            End If
        Catch ex As Exception
            MsgBox(ex.Message())
        End Try
    End Sub
End Class

VB.NET版+三層實現登陸