vb.net机房收费登录功能

         六月份已经过去11天了，着手vb.net也好几天了，但是仿佛看到机房收费有一种莫名的恐惧和兴奋，说道前面的三层只不过那是用C#编写的，但是我们的机房使用vb.net编写，所以我就用vb编写了关于登陆界面的代码。

    下面来看看U层代码：

Public Class Form1

    Private Sub btnOK_Click(sender As Object, e As EventArgs) Handles btnOK.Click
        '实例化一个ui层用到的实体类
        Dim Uuser As New Mobel.LoginMobel
        '将输入的内容，赋给实例化对象
        Uuser.userName = txtUserName.Text
        Uuser.passWord = txtPassword.Text

        If BLL.LoginBLL.isnullLoginBLL(Uuser) Then
            MsgBox("登录成功")
        Else
            MsgBox("登录失败")
        End If

    End Sub
End Class

    接着是实体层代码：  

Public Class LoginMobel
    Private MuserName As String
    Public Property userName() As String
        Get
            Return MuserName
        End Get
        Set(value As String)
            MuserName = value
        End Set
    End Property
    Private MpassWord As String
    Public Property passWord() As String
        Get
            Return MpassWord
        End Get
        Set(value As String)
            MpassWord = value
        End Set
    End Property

End Class

    下面是B层代码：

Public Class LoginBLL
    Public Shared Function isnullLoginBLL(ByVal UtextUser As Mobel.LoginMobel) As String
        Dim DtextUser As Mobel.LoginMobel
        Dim BtextUser As New DAL.LoginDAL

        DtextUser = BtextUser.LoginDALSelectUser(UtextUser.userName)

        If DtextUser Is Nothing Then
            Return False
        End If
        If UtextUser.passWord = DtextUser.passWord Then
            Return True
        Else
            Return False
        End If
    End Function
End Clas

    最后是D层代码：

Imports System.Data.SqlClient
Public Class LoginDAL
    Public Function LoginDALSelectUser(ByVal UserName As String) As Mobel.LoginMobel
        '建立数据库连接字符串
        Dim LoginConn As New SqlClient.SqlConnection("server=XZP-PC;database=Login;User ID=sa ;Password=123456")
        '建立数据库命令字符串
        Dim LoginCmm As New SqlClient.SqlCommand("SELECT UserName,Password FROM Users")
        '打开数据库
        LoginConn.Open()
        '定义数据库库读取方式
        Dim LoginReader As SqlDataReader
        '读取数据库中的内容
        LoginReader = LoginCmm.ExecuteReader

        Dim textUser As New Mobel.LoginMobel
        If LoginReader.Read() Then
            textUser.userName = LoginReader.GetFieldValue(Of String)(0)
            textUser.passWord = Trim(LoginReader.GetFieldValue(Of String)(1))

            Return textUser

            LoginReader.Close()
            LoginConn.Close()
        Else
            Return Nothing
        End If
    End Function
End Class

       在添加窗体引用时，出现了一点点的错误，让BLL，UI，DAL，MOBEL互相引用了，出现了下面的错误

       所以在添加引用方面要理解好三层之间的关系，才能做到万无一失！