.NET版三层登录

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       看着视频敲了一遍登录的例子，好像只是知道了三层里有D层、B层、U层，每层都是相互独立的，然后将数据逐层的传递。但是具体是怎么实现的，还是有点蒙……

       在敲.NET版三层登录之前参考了很多人的博客，这才慢慢的下手，敲上一遍，就觉得有清楚了很多……

       首先，建立以下的Windows应用程序以及类库：

实体类（Model）代码：

<span style="font-size:18px;">Public Class UserInfo
    Private _username As String
    'Private _ID As Decimal
    'Public Property ID As Decimal
    '    Get
    '        Return _ID

    '    End Get
    '    Set(value As Decimal)
    '        _ID = value
    '    End Set
    'End Property
    Public Property UserName As String
        Get
            Return _username
        End Get
        Set(ByVal value As String)
            _username = value

        End Set
    End Property
    Private _pwd As String
    Public Property Pwd As String
        Get
            Return _pwd
        End Get
        Set(value As String)
            _pwd = value

        End Set
    End Property

End Class
</span>

D层代码：（引用model实体类）

<span style="font-size:18px;">'引用命名空间
Imports System.Data
Imports System.Data.SqlClient
Imports Login.Model
'Imports LoginDAL



Public Class UserDAO
    '连接数据库
    'Dim sqlConnectStr As String = "sever=YU;database=Login;User ID =sa;Password=123456"
    'Dim sqlConnection1 As SqlConnection = New SqlConnection(sqlConnectStr)
    Public conn As New SqlConnection("server=YU;database=Login;User ID =sa;Password=123456")
    Public Function SelectUser(ByVal UserDAO As Login.Model.UserInfo) As Login.Model.UserInfo
        '传递实体参数UserInfo而不是id,name,这样也方便对实体中的参数进行调用
        Dim reader As SqlDataReader    '定义SqlDataReader对象
        Dim eUser As New Login.Model.UserInfo
        Dim sql As String = "select UserName,Password FROM Users WHERE UserName=@username and Password=@password"
        Dim cmd As New SqlCommand(sql, conn)   '定义sqlcommand对象

        cmd.CommandText = sql
        cmd.CommandType = CommandType.Text
        cmd.Parameters.Add(New SqlParameter("@username", UserDAO.UserName))
        cmd.Parameters.Add(New SqlParameter("@password", UserDAO.Pwd))

        conn.Open()
        reader = cmd.ExecuteReader
        While reader.Read()
            eUser.UserName = reader.GetString(0)
            eUser.Pwd = reader.GetString(1)

        End While
        Return UserDAO
        reader.Close()

    End Function
End Class
</span>

B层代码：（引用D层和model实体类）

<span style="font-size:18px;">Imports Login.DAL



Public Class LoginManager
    Public Function UserLogin(ByVal UserDAO As Login.Model.UserInfo) As Login.Model.UserInfo
        Dim uDao As New Login.DAL.UserDAO
        Dim eUser1 As New Login.Model.UserInfo

        eUser1 = uDao.SelectUser(UserDAO) '将数据传给D层
        '判断
        If IsNothing(eUser1.UserName) Then
            Throw New Exception("登录失败，请验证登录名和密码！")
        Else
            MsgBox("登录成功！")

            Return eUser1

        End If

    End Function

End Class
</span>

U层代码：（引用model实体类和B层）

<span style="font-size:18px;">Public Class Form1

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles btnOK.Click
        Try
            Dim eUser2 As New Login.Model.UserInfo
            Dim eUser3 As New Login.Model.UserInfo

            eUser2.UserName = txtUserName.Text.Trim '将U层数据传给实体
            eUser2.Pwd = txtPassword.Text

            Dim mgr As New Login.BLL.LoginManager '将数据传递给B层
            eUser3 = mgr.UserLogin(eUser2)
        Catch ex As Exception
            MessageBox.Show(ex.Message.ToString())
        End Try
    End Sub

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

      三层的特点是：U层、B层、D层都引用了实体类，但是实体类却不知道三层的存在。U层将数据传递给B层，B层进行处理，之后传递给D层，三层之间相互独立，如果哪一层发生变化，不会影响其他的层。总而言之：U层只负责显示和采集用户的信息和操作，B层只负责处理业务逻辑，D层只负责提供基本的数据访问。

.NET版三层登录

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原文地址：http://blog.csdn.net/xingyu0806/article/details/45786861