Public Class Form1
    '删除
    Private Sub btnDelete_Click(sender As Object, e As EventArgs) Handles btnDelete.Click
        Try
            '获得表现层的数据
            Dim muser As New LoginMODEL.User              '实例化一个新的实体，用来传递B层的实体
            muser.UserName = txtUserName.Text.Trim           '将用户名传递给实体层的UserName
            muser.PassWord = txtPassWord.Text.Trim            '将密码传递给实体层的PassWord

            '调用B层，登录判断
            Dim mgr As New LoginBLL.UserMananger
            Call mgr.DeleteBLL(muser)

        Catch ex As Exception
            MessageBox.Show(ex.Message.ToString())              '错误处理
        End Try
    End Sub
   

End Class

'删
Public Class UserMananger

    Public Sub DeleteBLL(ByVal User As LoginMODEL.User)


        Dim uDAO As New LoginDAL.SqlserverUser

        '查询用户是否存在，如果存在修改密码，如果不存在提示框
        Dim mUser As LoginMODEL.User
        mUser = uDAO.SelectDAL(User)

        If IsNothing(mUser.UserName) Then
            MsgBox("用户不存在，请重新输入", , "警告")
        Else
            Call uDAO.DeleteDAL(User)   '调用删除处功能
        End If
    End Sub


End Class

<span style="font-family:KaiTi_GB2312;font-size:24px;">' 引用命名空间
Imports System.Data
Imports System.Data.SqlClient
Imports LoginMODEL

'D层，主要是对原始数据（数据库或者文本文件等存放数据的形式）的操作层，需要引用实体层

Public Class SqlserverUser
    Public conn As New SqlConnection("server=ZY-PC;database=Login;user id=sa;password =1")          '创建数据库的连接
   
    '删
    Public Sub DeleteDAL(ByVal User As User)
        '引用化一个实体
        Dim sql As String = "delete from T_Users where UserName=@UserName and PassWord=@PassWord " '数据库删除语句
        Dim cmd As New SqlCommand(sql, conn)
        cmd.CommandText = sql
        cmd.CommandType = CommandType.Text
        cmd.Parameters.Add(New SqlParameter("@UserName", User.UserName))        '给变量@UserName赋值
        cmd.Parameters.Add(New SqlParameter("@PassWord", User.PassWord))        '给@PassWord赋值
        conn.Open()
        cmd.ExecuteNonQuery()           '执行对数据库的操作
        conn.Close()

    End Sub

  
End Class</span>