去年的时候，我写过一篇机房收费系统登陆的总结文章，那是站在VB的基础上，直接查询数据库实现的登陆。是非常初期的知识。假设想了解详情，请看VB查询数据库之登陆窗口——机房收费系统总结（一）。
今天。我要换一个角度。换一个方式。来实现登陆。首先，我选择的开发工具是VB.NET，数据库是SQLSever2008。
其次，我用的是三层的思想，把界面。逻辑和数据都分开。降低相互之间的影响。
在次。界面层尽量简洁。全部的算法和业务逻辑都写到逻辑层，同一时候使用了接口和工厂模式以及外观模式，降低了相互之间的依赖。降低了耦合。最后。通过文档和UML图。写出代码。实现登陆。
首先，看看我设计的登陆时序图（如有错误，欢迎指出。不胜感激）：
看到图之后。假设你拥有一定的经验，相信对你来说，代码就不是问题了吧。以下，我把我的代码放在以下，仅供參考哦！（对了，U层界面没有变。假设想知道。请看连接博客）。
首先是实体层代码：
用户实体层：
Public Class UserInfo
Private _userid As String
Private _password As String
Public Property UserID As String
Get
Return _userid
End Get
Set(value As String)
_userid = value
End Set
End Property
Public Property PassWord As String
Get
Return _password
End Get
Set(ByVal value As String)
_password = value
End Set
End Property
End Class
工作表实体层：
<span style="font-size:18px;">Imports System
Imports System.Data
''' <summary>
''' 数据库表OpeLineRecord所相应的实体类
''' </summary>
Public Class OpeLineRecordEntity
Private m_Opercomprecordid As String
Private m_Operatorid As String
Private m_Landdate As String
Private m_Landtime As String
Private m_Outdate As String
Private m_Outtime As String
Private m_Status As String
Private m_Computerid As String
Public Sub OpeLineRecordEntity()
m_Opercomprecordid = ""
m_Operatorid = ""
m_Landdate = ""
m_Landtime = ""
m_Outdate = ""
m_Outtime = ""
m_Status = ""
m_Computerid = ""
End Sub
''' <summary>
'''设置或返回值Opercomprecordid
''' </summary>
Public Property Opercomprecordid As String
Get
Return m_Opercomprecordid
End Get
Set(value As String)
m_Opercomprecordid = value
End Set
End Property
''' <summary>
'''设置或返回值Operatorid
''' </summary>
Public Property Operatorid As String
Get
Return m_Operatorid
End Get
Set(value As String)
m_Operatorid = value
End Set
End Property
''' <summary>
'''设置或返回值Landdate
''' </summary>
Public Property Landdate As String
Get
Return m_Landdate
End Get
Set(value As String)
m_Landdate = value
End Set
End Property
''' <summary>
'''设置或返回值Landtime
''' </summary>
Public Property Landtime As String
Get
Return m_Landtime
End Get
Set(value As String)
m_Landtime = value
End Set
End Property
''' <summary>
'''设置或返回值Outdate
''' </summary>
Public Property Outdate As String
Get
Return m_Outdate
End Get
Set(value As String)
m_Outdate = value
End Set
End Property
''' <summary>
'''设置或返回值Outtime
''' </summary>
Public Property Outtime As String
Get
Return m_Outtime
End Get
Set(value As String)
m_Outtime = value
End Set
End Property
''' <summary>
'''设置或返回值Status
''' </summary>
Public Property Status As String
Get
Return m_Status
End Get
Set(value As String)
m_Status = value
End Set
End Property
''' <summary>
'''设置或返回值Computerid
''' </summary>
Public Property Computerid As String
Get
Return m_Computerid
End Get
Set(value As String)
m_Computerid = value
End Set
End Property
End Class</span> 将Datatable转换为泛型
<span style="font-size:18px;">Imports System.Collections.Generic '添加泛型的命名空间
Imports System.Reflection
Public Class EntityHelper
Public Shared Function convertTolist(Of T As {New})(ByVal dt As DataTable) As IList(Of T) '将DataTable转化为泛型集合
'注意：1，convertToList（Of T As {New} 这里的New是用来约束T的，必须有，不然new T 的时候会出现错误
''2，new约束在C#和VB.NET里面的写法是不一样的。C#里面用的是where来为T加上约束的
Dim myList As New List(Of T) '定义终于返回的集合
Dim myType As Type = GetType(T) '得到实体类的类型么
Dim dr As DataRow '定义行集
Dim tempName As String = String.Empty '定义一个暂时变量
'遍历DataTable的全部数据行
For Each dr In dt.Rows
Dim myT As New T '定义一个实体类的对象
Dim propertys() As PropertyInfo = myT.GetType().GetProperties() '定义属性集合
Dim Pr As PropertyInfo
'遍历该对象的全部属性
For Each Pr In propertys
tempName = Pr.Name '将属性名称赋值给暂时变量
'检查DataTable是否包括此列（列名==对象的属性名）
If (dt.Columns.Contains(tempName)) Then '将此属性与DataTable里的列名比較。查看DataTable是否包括此属性
'推断此属性是否有Setter
If (Pr.CanWrite = False) Then '推断此属性是否可写，假设不可写，跳出本次循环
Continue For
End If
Dim value As Object = dr(tempName) '定义一个对象型的变量来保存列的值
If (value.ToString <> DBNull.Value.ToString()) Then '假设非空。则赋给对象的属性
Pr.SetValue(myT, value, Nothing) '在执行期间。通过反射，动态的訪问一个对象的属性
End If
End If
Next
myList.Add(myT) '加入到集合
Next
Return myList '返回实体集合
End Function
End Class
</span>
然后是接口层IDAL：
<span style="font-size:18px;">Public Interface IUser
Function SelectUser(ByVal user As entity.UserInfo) As List(Of UserInfo)
End Interface</span> D层：<span style="font-size:18px;">Imports IDAL
Imports entity
Imports System.Data.SqlClient
Public Class UserDAL : Implements IDAL.IUser
Public Function SelectUser(user As UserInfo) As List(Of UserInfo) Implements IUser.SelectUser
Dim strUserID As String = user.UserID
Dim helper As New Helper.Sqlhelper
Dim dt As New DataTable
Dim mylist As List(Of UserInfo)
Dim strSql As String = "select * from OperatorInfo where OperatorID=@UserID and state='使用'"
Dim sqlParams As SqlParameter() = {New SqlParameter("@UserID", strUserID)} '声明并实例化參数
dt = helper.ExecuteNonQuery(strSql, CommandType.Text, sqlParams) '调用SqlHelper类中的ExecSelect（）方法来运行查询。并获取返回值
mylist = EntityHelper.convertTolist(Of UserInfo)(dt) '将dt转换为泛型集合
Return mylist
End Function
End Function
End Class
</span>
添加记录
<span style="font-size:18px;">Imports IDAL
Imports entity
Imports System.Data.SqlClient
Public Class UserWorklogDAL : Implements IDAL.IUserWorklog
Public Function AddUserworklog(worklog As OpeLineRecordEntity) As Boolean Implements IUserWorklog.AddUserworklog
'声明一个SqlHelper类型的helper
Dim helper As New Helper.Sqlhelper
Dim dt As New Integer
'声明并实例化须要运行的SQL语句
Dim strSql As String = "Insert into OpeLineRecord (OperatorID,landDate,landTime,ComputerID,Status) values (@OperatorID,@landDate,@landTime,@ComputerID,@Status)"
'声明兵实例化參数数组
Dim sqlParams As SqlParameter() = {New SqlParameter("@OperatorID", worklog.Operatorid),
New SqlParameter("@LandDate", worklog.Landdate),
New SqlParameter("@LandTime", worklog.Landtime),
New SqlParameter("@ComputerID", worklog.Computerid),
New SqlParameter("@Status", worklog.Status)}
'调用SqlHelper类中的ExecAddDeleteUser（）方法来运行加入信息。获取返回值并Return
dt = helper.ExecAddDelUpdate(strSql, CommandType.Text, sqlParams)
Return dt
If dt > 0 Then
Return True
Else
Return False
End If
End Function</span>外观：
<span style="font-size:18px;">Public Class LoginFAC
Public Function Login(ByVal user As entity.UserInfo) As String
Dim userlogin As New BLL.UserManager
userlogin.IsUserExit(user)
If Not userlogin.IsUserExit(user) Then
Throw New Exception("password不对")
End If
userlogin.CheckPWDIsRight(user)
If userlogin.CheckPWDIsRight(user) = False Then
Throw New Exception("password不对")
End If
'推断用户是否登录了系统
Dim userwork As New entity.OpeLineRecordEntity
Dim workbll As New BLL.UserWorklogManager
userwork.Operatorid = user.UserID
userwork.Landdate = DateTime.Now.ToString("yyyy/MM/dd")
userwork.Landtime = DateTime.Now.ToString("HH:mm")
userwork.Computerid = System.Net.Dns.GetHostName()
userwork.Status = "正在值班"
'加入登录信息
workbll.AddWorklog(userwork)
End Function
End Class</span>
SQLhelper层：
<span style="font-size:18px;">'通过配置文件获取连接字符串
Imports System.Data
Imports System.Data.SqlClient
'Imports System.Configuration '加入对配置文件的引用
Public Class Sqlhelper
'调用配置文件
Private ReadOnly strConnection As String = Configuration.ConfigurationManager.AppSettings("ConnStr").ToString
'有參数的查询
'return DataTable 查询出的表格
Public Function ExecuteNonQuery(ByVal cmdText As String, ByVal cmdType As CommandType, ByVal sqlParams As SqlParameter()) As DataTable
Using conn As New SqlConnection(strConnection) '使用连接池。能够在使用完毕后自己主动关闭连接
Dim cmd As SqlCommand = conn.CreateCommand() '
Dim adp As SqlDataAdapter
Dim ds As New DataSet
cmd.CommandText = cmdText '须要运行的SQL语句
cmd.CommandType = cmdType '给出Sql语句的类型
cmd.Parameters.AddRange(sqlParams) '參数数组，參数个数依据实际情况而定
adp = New SqlDataAdapter(cmd)
Try
conn.Open()
adp.Fill(ds)
'Return cmd.ExecuteNonQuery()
Return ds.Tables(0)
Catch ex As Exception
Return Nothing
Throw ex
End Try
End Using
End Function
'有參数的增删改
Public Function ExecAddDelUpdate(ByVal cmdText As String, ByVal cmdType As CommandType, ByVal sqlParams As SqlParameter()) As Integer
Using conn As New SqlConnection(strConnection)
Dim cmd As SqlCommand = conn.CreateCommand()
Dim adp As SqlDataAdapter
Dim ds As New DataSet
cmd.CommandText = cmdText
cmd.CommandType = cmdType
cmd.Parameters.AddRange(sqlParams)
adp = New SqlDataAdapter(cmd)
Try
conn.Open()
adp.Fill(ds)
Return ds.Tables.Count
Catch ex As Exception
Return Nothing
Throw ex
End Try
End Using
End Function
End Class
</span>
工厂层：
<span style="font-size:18px;">Imports System.Reflection
Imports [IDAL]
Public Class BDFactory
'Private Shared ReadOnly db As String = Configuration.ConfigurationManager.AppSettings("DBString")
'Private Shared ReadOnly assemblyName = db + "DAL"
Private Shared ReadOnly assemblyName = "SQLDAL"
Public Function CreateUserDAO() As IDAL.IUser
'Dim className As String = assemblyName + "." + db + "UserDAL"
Dim className As String = assemblyName + "." + "UserDAL"
Return CType(Assembly.Load(assemblyName).CreateInstance(className), IUser) '返回IUser
End Function </span>
<span style="font-size:18px;">Public Function CreateUserworklogDAO() As IDAL.IUserWorklog
Dim strInstance As String = assemblyName + "." + "UserWorklogDAL" '所要实例化的对象（程序集与命名空间同名）
Return CType(Assembly.Load(assemblyName).CreateInstance(strInstance), IUserWorklog) '返回IUserWorklog
End Function</span>
B层：
加入上机记录
<span style="font-size:18px;">Imports Factory
Imports entity
Public Class UserWorklogManager
Private ReadOnly factory As Factory.BDFactory = New Factory.BDFactory
Dim iu As IDAL.IUserWorklog '声明并实例化变量iuser为：调用factory.CreateUserDAO（）方法所返回来的IUser
'加入用户工作记录
Public Function AddWorklog(ByVal worklog As entity.OpeLineRecordEntity) As Boolean
iu = factory.CreateUserworklogDAO()
Dim dt As Integer
dt = iu.AddUserworklog(worklog)
If dt > 0 Then
Return True
Else
Return False
End If
End Function
</span> 查询用户是否存在 password是否正确<span style="font-size:18px;">Imports entity
Public Class UserManager
Private ReadOnly factory As Factory.BDFactory = New Factory.BDFactory()
Dim iuser As IDAL.IUser
Public Function IsUserExit(ByVal user As entity.UserInfo) As Boolean
Dim iu As IDAL.IUser
Dim mylist As List(Of UserInfo)
iu = factory.CreateUserDAO()
mylist = iu.SelectUser(user)
If mylist.Count = 0 Then
Return False
Else
Return True
End If
End Function
Public Function CheckPWDIsRight(ByVal user As entity.UserInfo) As Boolean
Dim iu As IDAL.IUser
Dim mylist As List(Of UserInfo)
iu = factory.CreateUserDAO()
mylist = iu.SelectUser(user)
If Trim(mylist(0).PassWord) <> user.PassWord Then
Throw New Exception("输入password不对")
Return False
Else
Return True
End If
End Function</span>最后是U层
<span style="font-size:18px;">Public Class frmlogin
Private Sub BtnOK_Click(sender As Object, e As EventArgs) Handles BtnOK.Click
Dim user As New entity.UserInfo '实例化User
user.UserID = txtUserName.Text
user.PassWord = txtPassword.Text
If txtUserName.Text.Trim().Length > 20 Then
MessageBox.Show("不能超过20位数字", "提示")
Exit Sub
End If
If txtUserName.Text.Trim() = "" Then
MessageBox.Show("请输入username", "提示", MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
Exit Sub
ElseIf txtPassword.Text.Trim() = "" Then
MessageBox.Show("请输入用password", "提示", MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
Exit Sub
End If
Try
'调用外观
Dim loginfac As Facade.LoginFAC = New Facade.LoginFAC()
loginfac.Login(user)
Me.Hide()
ForMain.Show()
Catch ex As Exception
MsgBox(ex.Message, CType(vbOKOnly + MsgBoxStyle.Information, MsgBoxStyle), "提示")
End Try
End Sub
End Class
</span> Ok 系统结束，可能会有轻微的问题，细心就一定会解决（由于在粘贴的过程中，可能一不留神。你懂得……）。相对第一次来说，代码和逻辑上，并没有简单，并且反倒难了。那我们为什么还有继续呢？
不知道读者是否有这种疑问。事实上，非常easy，尽管代码和逻辑麻烦了，可是系统的性能更好了，逻辑也更清楚了，同一时候，降低了U层的负担。工作详细化。相同，兼容性扩展性更好了，健壮性也有所提高。更加适合合作开发。
这是一个小系统，假设是大系统，是不是优势就会更明显呢！