【开篇】

  小编对于C#刚入门，Vb.net也是初学者，但是有一颗敢做的心，每天逼迫自己进步这是小编现在的生活。对于编程，以小编看来，就是高仿，模仿实例，在调试代码中成长，代码不是看会而是敲会的，纠结好久的问题也就迎刃而解。问题是我看着其他人的代码敲，自己什么都没有学会啊，都是别人的。接触新知识，大家可能都会有这样的一个认识，很吃力，很费劲。类似于我们小时候学骑自行车的时候，总是摔倒一样的，起先敲代码，大多的时候都是在调试错误中，不断总结经验，才可以敲出正确的代码。让我们一起骑车去看风景吧！！！

【VB.net版】

Entity层：

<span style="font-family:KaiTi_GB2312;font-size:18px;"><strong>using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace LoginModel
{
    public class UserInfo
    {
        
        public string UserName { get; set; }
        public string Password { get; set; }
        

    }
}
</strong></span>

<span style="font-family:KaiTi_GB2312;font-size:18px;"><strong>Imports Model
Imports BLL
Public Class Form1

    Private Sub btnLogin_Click(sender As Object,e As EventArgs) Handles btnLogin.Click
        Try
            Dim euser2 As New Model.User
            '实例化一个user，用来传递B层的实体
            Dim euser3 As Model.User
            '定义一个类型为users的参数，用来赋值
            euser2.UserName = txtUsername.Text.Trim '将用户名传给实体层的UserName
            euser2.password = txtPassword.Text.Trim    '将密码传给实体层的PassWord

            '调用B层，登录判断
            Dim mgr As New BLL.LoginManager
            euser3 = mgr.UserLogin(euser2)

        Catch ex As Exception
            MessageBox.Show(ex.Message.ToString())

        End Try
    End Sub
End Class
</strong></span>

<span style="font-family:KaiTi_GB2312;font-size:18px;"><strong>Public Class LoginManager
    Public Function UserLogin(ByRef User As Model.User) As Model.User
        Dim uDAO As New LoginDAL.UserDAO    '实例化D层中心的UserDAO对象
        Dim euser1 As Model.User     '定义一个类型为实体层User的参数，用于赋值

        euser1 = uDAO.SelectUser(User)

        '判断是否查询到记录,若有,登录成功,并返回实体user1
        If IsNothing(euser1.UserName) Then
            Throw New Exception("登录失败，请检查用户名和密码！")
        Else

            MsgBox("登录成功！")
            Return euser1
        End If

    End Function
End Class
</strong></span>

<span style="font-family:KaiTi_GB2312;font-size:18px;"><strong>Imports System.Data
Imports System.Data.sqlClient
Imports Model
'D层，只涉及到对数据的操作，需要引用实体层Model
Public Class UserDAO
    '创建数据库连接
    Public conn As New sqlConnection("Server=(local);Database=Login;user id=sa;password=6")

    Public Function SelectUser(ByRef User As User) As Model.User

        Dim reader As sqlDataReader
        Dim eUser As New Model.User

        Dim sql As String = "Select * From Users Where UserName=@Username And Password=@password"
        Dim cmd As New sqlCommand(sql,conn)
        cmd.CommandText = sql

        cmd.CommandType = CommandType.Text

        cmd.Parameters.Add(New sqlParameter("@Username",User.UserName))

        cmd.Parameters.Add(New sqlParameter("@password",User.password))

        conn.Open()
        reader = cmd.ExecuteReader()

        While reader.Read()
            eUser.UserName = reader.GetString(0)
            eUser.password = reader.GetString(1)

        End While
        Return eUser
        conn.Close()


    End Function
End Class
</strong></span>