机房重构前奏——三层转七层

       刚敲完三层的小例子之后，感觉还是很简单的，只是通过分层让不同的层次完成不同的工作，减少耦合性。可是接下来师父就直接给了一个大难题，让我将三层转变为七层，这对我来说相当困难，自己当时根本就不知道有哪几层，就开始搜。经过一段时间的思考后，终于能够初步明白登录的七层是那些了。下面是我画的包图：

       三层的时候只有UI、BLL、DAL，七层只是在原来基础上添加了外观设计模式、接口和抽象工厂，通过分层来减小耦合度。接下来如何来实现各层之间的链接呢？

U层：表示层，主要负责与界面设置。

Imports Facade   '引入外观
Imports Entity  '引入实体


Public Class frmLogin
    Private Sub btnConfirm_Click(sender As Object, e As EventArgs) Handles btnConfirm.Click
        If txtUserID.Text = "" Then
            MessageBox.Show("请输入用户名")
            txtUserID.Text = ""
            txtUserID.Focus()
            Exit Sub
        ElseIf txtPassword.Text = "" Then
            MessageBox.Show("请输入密码")
            txtPassword.Text = ""
            txtPassword.Focus()
            Exit Sub
        End If

        Try
            Dim facadeLogin As New Facade.LoginFacade
            Dim User As New En_User
            User.ID = txtUserID.Text.Trim()
            User.Password = txtPassword.Text.Trim()
            Dim flag As Boolean

            flag = facadeLogin.CheckUser(User)

            If flag = False Then
                MsgBox("用户不存在")
                txtUserID.Text = ""
                txtPassword.Text = ""
                txtUserID.Select()
                txtUserID.Focus()
            End If

            Dim table As DataTable
            table = facadeLogin.CheckPwd(User)
            If Trim(txtPassword.Text) = Trim(table.Rows(0).Item(1)) Then
                MsgBox("登录成功")
                txtUserID.Text = ""
                txtPassword.Text = ""
            End If
        Catch
            MsgBox("用户不存在或者密码不正确")
            txtUserID.Text = ""
            txtPassword.Text = ""
            txtUserID.Select()
            txtUserID.Focus()

        End Try
    End Sub

    Private Sub btnCancel_Click(sender As Object, e As EventArgs) Handles btnCancel.Click
        Me.Close()
    End Sub
End Class

Facade层：这一层采用外观模式，通过外观模式使U层不直接和BLL层接触，减少B层和U层之间的耦合，当然这样做现在看起来好像有点繁琐，使我们本来简单的系统复杂化，但在大项目中能够体现其优越性。

Imports BLL     '引用BLL层
Imports Entity  '引用实体

Public Class LoginFacade
    Public Function CheckUser(ByVal User As En_User) As Boolean

        '用于检查用户是否存在
        Dim IsUserExists As New BLL.LoginBLL()
        Dim flag As Boolean
        flag = IsUserExists.IsUserExits(User)
        If flag = True Then
            Return True
        Else
            Return False
        End If
    End Function

    '检查密码是否正确
    Public Function CheckPwd(ByVal User As En_User) As DataTable
        Dim IsPwd As New BLL.LoginBLL()
        Dim table As DataTable
        table = IsPwd.isPWDright(User)
        Return table
    End Function

End Class

BLL层：接下里就将值传给B层，交由其处理，BLL层主要对业务逻辑进行管理，相当于就是对一个业务的处理。比如登录你就需要验证用户是否存在，密码是否正确，这一层将分开的功能组合到一块来完成一个业务。

Imports IDAL        '引用IDAL
Imports Factory     '引用Factory
Imports Entity      '应用实体
Public Class LoginBLL
    Public Function IsUserExits(ByVal User As En_User) As Boolean
        Dim factory As New DateAccess
        Dim IUser As IUserLogin

        '调用创建用户的工厂方法
        IUser = factory.CreateUser

        Dim table As DataTable
        Dim flag As Boolean
        table = IUser.CheckUser(User)

        If table.Rows.Count > 0 Then
            flag = True
        Else
            flag = False
        End If
        Return flag
    End Function
    Public Function IsPWDright(ByVal User As En_User) As DataTable
        Dim factory As New DateAccess
        Dim Iuser As IDAL.IUserLogin
        Dim table As DataTable

        Iuser = factory.CreateUser
        table = Iuser.CheckUser(User)
        Return table
    End Function
End Class

Factory层：抽象工厂+反射+配置文件

Imports IDAL    '引入IDAL
Imports System.Configuration    '引入配置文件    
Imports System.Reflection
Public Class DateAccess
    Private Shared ReadOnly paceName As String = "DAL"
    Private Shared ReadOnly db As String = ConfigurationManager.AppSettings("<span style="color:#ff0000;">DB</span>")
    Public Function CreateUser() As IUserLogin
        Dim className As String = paceName + "." + db + "LoginDAL"
        Dim iuser As IDAL.IUserLogin
        iuser = CType(Assembly.Load(paceName).CreateInstance(className), IUserLogin)
        Return iuser
    End Function
End Class

配置文件：

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <startup>
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
    </startup>
    <appSettings>
      <add key ="<span style="color:#ff0000;">DB</span>" value ="Sql"></add>
      <add key ="ConnString" value ="Server=.;DataBase=Login;User ID =sa;Password =1"/>
    </appSettings>
</configuration>

标注红字的部分一定要对应，否则就会出现问题。

IDAL层：也就是接口层，实现和DAL层的连接，接口达到了统一访问的目的，另外通过接口方便DAL层的工作分配。

Imports Entity      '引用实体
Public Interface IUserLogin
    Function CheckUser(ByVal enuser As En_User) As DataTable
End Interface

DAL层：主要是用来对表进行操作，通过SQL Helper来和数据库连接。

Imports Entity
Imports System.Data
Imports System.Data.SqlClient
Public Class SqlLoginDAL : Implements IDAL.IUserLogin
    Public Function UserLoginDAL(ByVal enuser As En_User) As DataTable Implements IDAL.IUserLogin.CheckUser
        Dim cmdText As String = "select * from Users where ID=@userID"
        Dim sqlparams As SqlParameter() = {New SqlParameter("@userID", enuser.ID)}
        Dim helper As New sqlHelper<span style="white-space:pre">	</span>'用于连接数据库
        Dim table As New DataTable
        table = helper.ExecSelect(cmdText, CommandType.Text, sqlparams)
        Return table<span style="white-space:pre">			</span>'返回记录
    End Function
End Class

       通过将登陆由三层转变为七层，对与变量之间的传递和调用关系理解的更清楚了，虽然还有一些欠缺，相信在接下来的机房重构中，会理解的更加深刻。。。