七层学习

                                                       七层学习

        七层就是在三层的基础之上，添加了外观层—设计模式的外观模式、抽象工厂、反射、接口层。

       外观层：主要是把UI和BLL层分离。

       抽象工厂加反射：主要是为了更换数据库的方便性，同时把DAL层中的类转换成为IDAL层中的接口，从而使BLL层实现通过调用IDAL从而调用DAL层。

        接口层：把BLL和DAL分离。

       七层从UI层开始，逐层依赖于下一层。除了SqlHelper和Factory之外的所有的层，都要添加对Entity层的引用，这里是关联关系，因为所有的层在使用实体层的时候，首先都先要对实体进行实例化，即New一个实体，而DAL层实现的是IDAL层中的方法，同时依赖于SqlHelper实现它自己的功能。

        通过反射，实例化D层的类，调用dll方法。将B层的参数通过反射的方法， 在D层做具体实现。

        Sqlhelper封装了对数据库的增删改查，减少了代码的量，提高了系统性能。

各层的具体代码：

UI层

     Public Class FrmLogin       Private Sub btnLogin_Click(sender As Object, e As EventArgs) Handles btnLogin.Click            '判断文本框是否为空          If txtUserID.Text = "" Then              MessageBox.Show("请您输入用户名！", "", MessageBoxButtons.OK, MessageBoxIcon.Exclamation)              txtUserID.Focus()              Exit Sub          ElseIf txtPWD.Text = "" Then              MessageBox.Show("请您输入密码！", "", MessageBoxButtons.OK, MessageBoxIcon.Exclamation)              txtPWD.Focus()              Exit Sub          End If              Dim User As New Entity.T_UserEntity          User.UserID = txtUserID.Text.Trim()          User.PWD = txtPWD.Text.Trim()            Dim Result As String          Dim facade As New Facade.LoginFacade          Result = facade.Login(User)            '用户名和密码验证的几种情况          Select Case Result              Case "此用户不存在"                  MsgBox("此用户不存在，请重新输入用户名！")                  txtUserID.Focus()                  txtUserID.SelectAll()              Case "密码错误"                  MsgBox("密码错误，请重新输入密码！")                  txtPWD.Focus()                  txtPWD.SelectAll()              Case "登陆成功"                  MsgBox("恭喜您，登录成功！")                  NowUser = txtUserID.Text.Trim()                  FrmMain.Show()                  Me.Hide()          End Select        End Sub        Private Sub btnCancel_Click(sender As Object, e As EventArgs) Handles btnCancel.Click          End      End Sub    End Class

Façade层

Public Class LoginFacade      Public Function Login(ByVal User As Entity.T_UserEntity) As String          Dim Userbll As New BLL.LoginBLL            '调用B层的方法验证用户名和密码是否正确          If Userbll.CheckUser(User) = False Then              Return "此用户不存在"          Else              If Userbll.CheckPWD(User) = False Then                  Return "密码错误"              Else                  Return "登陆成功"              End If          End If      End Function    End Class

BLL层

Public Class LoginBLL      '验证用户名是否正确      Public Function CheckUser(ByVal user As Entity.T_UserEntity) As Boolean          Dim Iuser As IDAL.LoginIDAL          Dim factory As New Factory.LoginFactory          Iuser = factory.CreateUserDAO()            Dim mylist As New List(Of Entity.T_UserEntity)          mylist = Iuser.SelectUserID(user)          If mylist.Count = 0 Then              Return False          Else              Return True          End If        End Function        '验证密码是否正确      Public Function CheckPWD(ByVal password As Entity.T_UserEntity) As Boolean          Dim Iuser As IDAL.LoginIDAL          Dim factory As New Factory.LoginFactory          Iuser = factory.CreateUserDAO            Dim mylist As New List(Of Entity.T_UserEntity)          mylist = Iuser.SelectPWD(password)          If mylist.Count = 0 Then              Return False          Else              Return True          End If      End Function    End Class

Factory层

Imports System.Reflection  Imports System.Configuration     Public Class LoginFactory      Dim DB As String = System.Configuration.ConfigurationSettings.AppSettings("DBss")      Private Shared ReadOnly assemblyName = "DAL"        Public Function CreateUserDAO() As IDAL.LoginIDAL           Dim className As String = assemblyName + "." + DB + "LoginDAL"          Return CType(Assembly.Load(assemblyName).CreateInstance(className), IDAL.LoginIDAL)        End Function  End Class

IDAL层

Public Interface LoginIDAL      Function SelectUserID(ByVal User As Entity.T_UserEntity) As List(Of Entity.T_UserEntity)      Function SelectPWD(ByVal User As Entity.T_UserEntity) As List(Of Entity.T_UserEntity)  End Interface

DAL层

Public Class SqlServerLoginDAL : Implements IDAL.LoginIDAL        Public Function SelectUserID(User As Entity.T_UserEntity) As List(Of Entity.T_UserEntity) Implements IDAL.LoginIDAL.SelectUserID            Dim sqlParams As SqlParameter() = {New SqlParameter("@UserID", User.UserID)}          Dim strSql As String = "select*from T_User where UserID=@UserID"            '实例化SqlHelper          Dim helper As New SqlHelper            Dim table As New DataTable          Dim mylist As New List(Of Entity.T_UserEntity)          table = helper.GetDataTable(strSql, CommandType.Text, sqlParams)          mylist = ConvertHelper.ConvertList(Of Entity.T_UserEntity)(table)            '返回泛型          Return mylist        End Function        Public Function SelectPWD(User As Entity.T_UserEntity) As List(Of Entity.T_UserEntity) Implements IDAL.LoginIDAL.SelectPWD            Dim sqlParams As SqlParameter() = {New SqlParameter("@UserID", User.UserID), New SqlParameter("@PWD", User.PWD)}          Dim strSql As String = "select*from T_User where UserID=@UserID and PWD=@PWD"            '实例化SqlHelper          Dim helper As New SqlHelper            Dim table As New DataTable          Dim mylist As New List(Of Entity.T_UserEntity)          table = helper.GetDataTable(strSql, CommandType.Text, sqlParams)          mylist = ConvertHelper.ConvertList(Of Entity.T_UserEntity)(table)            '返回泛型          Return mylist        End Function  End Class

Entity层

Private _UserID As String      Private _PWD As String      Private _Level As String      Private _UserName As String      Private _Head As String        Public Property UserID As String          Get              Return _UserID          End Get          Set(value As String)              _UserID = value          End Set      End Property        Public Property PWD As String          Get              Return _PWD          End Get          Set(value As String)              _PWD = value          End Set      End Property        Public Property Level As String          Get              Return _Level          End Get          Set(value As String)              _Level = value          End Set      End Property        Public Property UserName As String          Get              Return _UserName          End Get          Set(value As String)              _UserName = 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  End Class

       七层的学习总是在参考博客，学到了很多东西，棒棒的，就像米老师今天说的站在巨人的肩膀上学习。