学步园

Public Class frmLogin

    Private Sub btnOk_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnOk.Click
        '定义实例
        Dim en_User As New Entity.en_UserInfo
        Dim bl_User As New BLL.bl_Login

        '赋值
        en_User.UserID = txtUserName.Text.Trim
        en_User.Password = txtPassword.Text.Trim
        '采集用户信息，展示登录结果
        If bl_User.LoginManager(en_User) Then
            MsgBox("登陆成功")
        Else
            MsgBox("登录失败")
        End If


    End Sub

    Private Sub btnCancel_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCancel.Click
        Me.Close()
    End Sub
End Class

Imports Entity
Imports DAL.dal_Login

Public Class bl_Login
    Public Function LoginManager(ByVal User As Entity.en_UserInfo) As Boolean
        Dim dal_User As New DAL.dal_Login
        Dim en_User As New Entity.en_UserInfo
        en_User.UserID = User.UserID

        '调用D层的方法
        'en_User = dal_User.selectUser(en_User)
        en_User = dal_User.selectUser(User)
        '判断操作
        If en_User.UserID.Trim = User.UserID And en_User.Password.Trim = User.Password Then
            Return True
        Else
            Return False
        End If
    End Function
End Class

Imports Entity

Public Class en_UserInfo
    '声明UserID属性
    Private e_UserID As String
    Public Property UserID As String
        Get
            Return e_UserID
        End Get
        Set(ByVal value As String)
            e_UserID = value
        End Set
    End Property

    '声明Password属性
    Private e_Password As String
    Public Property Password As String
        Get
            Return e_Password
        End Get
        Set(ByVal value As String)
            e_Password = value
        End Set
    End Property
End Class

４. DAL层
作用主要是与操作数据库
(1) 从数据源加载数据（select）
(2) 向数据源写入数据（insert/update）
(3) 从数据源删除数据（delete）

Imports Entity
Imports System.Data.SqlClient
Imports System.Data


Public Class dal_Login

    '连接数据库
    Dim strConn As String = "server =192.168.24.59;database=Login;uid=sa;pwd=123456"
    Dim sqlConnect As SqlConnection = New SqlConnection(strConn)

    '自定义检查参数
    Function selectUser(ByVal User As Entity.en_UserInfo) As Entity.en_UserInfo

        Dim read As SqlDataReader
        Dim en_User As New Entity.en_UserInfo

        '其实下面的这段程序就相当于dim sql as string ="select  ID,UserName,PWD From Users Where UserName='"User.UserName"' And PWD='"User.PWD"'"
        '而写成这个程序块是为了防止Sql注入，即安全性考虑。
        '@UserName相当于传了一个参数，（"@UserName", User.UserName）相当于给参数名字传递了参数。
        Dim sql As String = "Select UserID,Password From UserInfo Where UserID=@UserID And Password=@Password"
        Dim sqlCmd As SqlCommand = New SqlCommand(sql, sqlConnect) '创建sqlCommand对象    


        'Dim UserDataTable As New DataTable  '定义一个DataTable对象


        sqlCmd.CommandText = sql  '获取SQL语句的具体内容
        sqlCmd.CommandType = CommandType.Text  '获取上述SQL语句的具体类型，在此为Select
        sqlCmd.Parameters.Add(New SqlParameter("@UserID", User.UserID))  '若用成eUser.UserName则会出现参数未传递的错误提示
        sqlCmd.Parameters.Add(New SqlParameter("@Password", User.Password))

        sqlConnect.Open()
        read = sqlCmd.ExecuteReader()       '执行查询语句，并生成一个DataReader
        read.Read()

        '读取查询到的数据，并返回给相应的属性
        While read.Read() '获取数据库中相应字段的数据
            '数组必须从零开始读取，否则会超出其界限
            User.UserID = read.GetString(0)
            User.Password = read.GetString(1)
        End While

        '如果用户存在的话，将数据库表中检索的记录对应赋值给参数
        'User.UserID = read.Item("UserID")
        'User.Password = read.Item("Password")

        Return User '返回查询到的实体
        sqlConnect.Close()

    End Function

End Class