在三层的地方也炖了不少时间了，再炖就烂了，找好了时机，趁大家不注意，总结一下：

从上面的这幅导图中，就可以看到，由U层（表示层） 引用 B层（逻辑判断层）和 Entity（实体“层”），由 B层 引用 D层和实体层，由D层引用实体层，也就是

只能单向引用，不可反复

下面，还是由实例来说明耕层之间的关系：

充值之界面：

                     

充值之U层：

Public Class Form1    Private Sub btnOK_Click(sender As Object, e As EventArgs) Handles btnOK.Click        Try            Dim eUser2 As New EntityRecharge.RechargeInfo            Dim eUser3 As EntityRecharge.RechargeInfo            eUser2.IDcard = Trim(txtIDcard.Text)            eUser2.AddCash = Trim(txtAddCash.Text)            Dim mgr As New RechargeBLL.RechargeManager            eUser3 = mgr.RechargeSc(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 SubEnd Class

充值之B层：

Public Class RechargeManager    Public Function RechargeSc(ByVal User As RechargeInfo) As EntityRecharge.RechargeInfo        Dim rDAO As New RechargeDAL.RechargeDAO        Dim eUser1 As Boolean        eUser1 = rDAO.SelectUser(User)        '寻找卡号        If eUser1 = False Then                '返回FALSE 代表  查找失败，也就是卡号未注册            Throw New Exception("卡号不存在，充值失败")        Else            eUser1 = rDAO.UpdateCash(User)     '查找成功，执行充值操作            If eUser1 = True Then                MsgBox("充值成功")            Else                Throw New Exception("充值失败")            End If        End If        Return User    End FunctionEnd Class

充值之D层：

Public Class RechargeDAO    Public conn As New SqlConnection("server=.;database=Login;user id=sa;password=li")    Public Function SelectUser(ByVal User As RechargeInfo) As Boolean        Dim eUser As New EntityRecharge.RechargeInfo        Dim reader As SqlDataReader        'Dim intNum1 As Integer        Dim sql As String = "SELECT * FROM Recharge WHERE IDcard=@IDcard"        Dim cmd As New SqlCommand(sql, conn)        cmd.CommandText = sql                     '获取SQL语句的具体内容        cmd.CommandType = CommandType.Text         '获取上述SQL语句的具体类型，在此为Select        cmd.Parameters.Add(New SqlParameter("@IDcard", User.IDcard)) '若用成eUser.UserName则会出现参数未传递的错误提示        'MsgBox(conn.State)        conn.Open()        reader = cmd.ExecuteReader        While reader.Read            eUser.IDcard = reader.GetInt32(0)        End While        conn.Close()        If eUser.IDcard = Nothing Then            Return False        Else            Return True        End If    End Function    Public Function UpdateCash(ByVal User As RechargeInfo) As Boolean        Dim intNum As Integer        Dim eUser As New EntityRecharge.RechargeInfo        Dim sql As String = "INSERT INTO Recharge (IDcard,AddCash,Cash) VALUES (@IDcard,@AddCash,@Cash)"        Dim cmd As New SqlCommand(sql, conn)        cmd.CommandText = sql        cmd.CommandType = CommandType.Text        cmd.Parameters.Add(New SqlParameter("@IDcard", User.IDcard))        cmd.Parameters.Add(New SqlParameter("@AddCash", User.AddCash))        cmd.Parameters.Add(New SqlParameter("@Cash", 11 + User.AddCash))        conn.Open()                   '打开连接        intNum = cmd.ExecuteNonQuery()     '返回 受影响行数        conn.Close()        '关闭连接        If intNum = 1 Then            Return True        Else            Return False       '返回 处理结果        End If    End FunctionEnd Class

Entity层：

Public Class RechargeInfo    Dim _idcard As Integer    Dim _cash As Integer    Dim _addcash As Integer    Public Property IDcard As Integer          '设置IDcard属性        Get            Return _idcard        End Get        Set(value As Integer)            _idcard = value        End Set    End Property    Public Property AddCash As Integer          '设置AddCash属性        Get            Return _addcash        End Get        Set(value As Integer)            _addcash = value        End Set    End Property    Public Property Cash As Integer             '设置Cash属性        Get            Return _cash        End Get        Set(value As Integer)            _cash = value        End Set    End PropertyEnd Class

其实吧，这篇和登录那片是差不多的，不一样的地方是，这次在查询的时候，我都用的是Boolean返回值，也就是说，我不需要你查询的数据，我只需要你查询的结果代表的意义，有没有这条数据，有就直接告诉我有，没有就直接告诉我没有，不需要再去比对