一、框架的搭建

U層引用Model層

B層引用Model層和DAL層

D層引用Model層和數據庫連接ImportsSystem.Data.SqlClient??

二、UML圖

1、類圖

U層：Windows1

B層：LoginUser

D層：UserDAO

Model層：UerEn

2、時序圖

3、包圖（設計模式在代碼中未體現，以后補充）

Link用來存儲連接字符串及SQL語句（以后補充）

三、代碼展示

1、實體類

[vb]?view plaincopy

<span?style="font-size:18px;">Public?Class?UserEn??

'定義所用到的屬性??

????Private?_userName?As?String??

????Public?Property?UserName?As?String??

????????Get??

????????????Return?_userName??

????????End?Get??

??

????????Set(ByVal?value?As?String)??

???????????_userName?=?value??

????????End?Set??

????End?Property??

??

????Private?_password?As?String??

????Public?Property?Password?As?String??

????????Get??

????????????Return?_password??

????????End?Get??

??

????????Set(ByVal?value?As?String)??

????????????_password?=?value??

????????End?Set??

????End?Property??

End?Class</span>??

2、U層

[vb]?view plaincopy

<span?style="font-size:18px;">Imports?Login.BLL???????????'層中引用，在調用對象時不用寫命名空間名??

Imports?Model??

Public?ClassStartWindow??

??

????'退出程序??

????Private?Sub?btnexit_Click(sender?As?Object,e?As?EventArgs)?Handles?btnexit.Click??

????????End??

????End?Sub??

????'登錄??

??

????Private?Sub?btnOK_Click(sender?As?Object,?eAs?EventArgs)?Handles?btnOK.Click??

????????Try??

??

????????????Dim?user1?As?New?UserEn?????????????????'實例化實體類，user1為實體類的對象??

????????????Dim?check?As?New?LoginUser??????????????'實例化B層的LoginUser類??

????????????Dim?user?As?Boolean????????????????????'定義布爾型變量，用來返回（也可定義為實體類型，返回實體類）??

??????????????

<span?style="font-size:18px;">????????????</span>user1.UserName?=txtUserName.Text.Trim????'把文本框用戶名賦給實體類中的UserName??

????????????user1.Password?=txtPassword.Text??????????'同理??

??

????????????If?txtUserName.Text?=?""Then??????????????'判斷用戶名文本框是否為空??

???????????????MessageBox.Show("請輸入用戶名！")??

????????????End?If??

??

????????????If?txtPassword.Text?=?""Then???????????????'同理??

???????????????MessageBox.Show("請輸入密碼！")??

????????????End?If??

????????????user?=?check.Login(user1)??????????????????'把B層Loin方法判斷返回的值賦予user，左右同時為真則登錄成功??

????????????MessageBox.Show("成功登錄！")??

????????Catch?ex?As?Exception???????????????????????????'捕獲從B/D層拋出的異常??

??

????????????MsgBox(ex.Message)??

????????End?Try??

????End?Sub??

End?Class</span>??

3、B層

[vb]?view plaincopy

<span?style="font-size:18px;">Imports?Model??

Imports?Login.DAL??

??

Public?ClassLoginUser??

??

????Function?Login(ByVal?user1?As?Model.UserEn)As?Boolean??

????????Dim?Dal?As?New?UserDAO?????????????'實例化D層UserDAO對象??

????????Dim?user2?As?Boolean????????????????'定義變量??

??

????????user2?=?Dal.SelectUser(user1)??????'調出D層方法SelectUser??

????????'判斷返回結果???

????????If?user2?Then??

????????????Return?True??

????????Else??

????????????Throw?NewException("登錄失敗!")??

????????????Exit?Function??

????????End?If??

????End?Function??

End?Class</span>??

4、D層

[vb]?view plaincopy

<span?style="font-size:18px;"><span?style="font-size:18px;">Imports?Model??

ImportsSystem.Data.SqlClient???????????'數據庫連接需引用??

ImportsSystem.Data.SqlClient.SqlCommand??

Public?Class?UserDAO??

??

????'連接數據庫??

????'SqlConnection表示一個到?SQL?Server數據庫的打開的連接。此類不能被繼承。??

????Dim?connDB?As?String?="Server=.;Database=MyLogin;User?ID=sa;Password=123;"??

????Dim?connSQL?As?SqlConnection?=?NewSqlConnection(connDB)??

??

????Function?SelectUser(ByVal?user1?AsModel.UserEn)?As?Boolean??

??

????????'把要執行的SQL語句賦給字符串變量sql??

??

????????Dim?sql?As?String?=?"select?*?FromUserInfo?where?UserID=@UserName?AND?Password=@Password;"??

????????Dim?cmd?As?SqlCommand?=?NewSqlCommand(sql,?connSQL)?????????'執行查詢語句??

??

???

??

????????'通過把實體的相關內容賦給參數，再將參數帶到數據庫對比（防止SQL注入）??

??

????????cmd.Parameters.Add(NewSqlParameter("@UserName",?user1.UserName))??

????????cmd.Parameters.Add(NewSqlParameter("@Password",?user1.Password))??

??

????????'打開連接，讀取數據??

??

????????connSQL.Open()??

????????Dim?read?As?SqlDataReader?=cmd.ExecuteReader()??

??

????????'若存在數據則返回True，否則相反??

??

????????If?read.Read()?Then??

????????????Return?True??

????????Else??

????????????Return?False??

????????????Exit?Function??

????????End?If??

????End?Function??

End?Class</span>??

</span>??

結果：

四、知識點小結

1、傳實體與傳參數區別

??????? 在參數較少的情況下，使用傳參比較方便；用的參數較多建議使用傳實體，效率較高

注意：如果在界面上顯示數據則設計到對實體的拆裝箱操作

例子：C#語言

[csharp]?view plaincopy

<span?style="font-size:18px;">?user.ID?=?reader.GetInt32(0);??

?user.UserName?=?reader.GetString(1);??

?user.Password?=?reader.GetString(2);??

??if(!reader.IsDBNull(3))??

??

?{??

???user.Email?=?reader.GetString(3);??

}</span>??

2、每層引用與單層Imports引用區別

層與層間引用：可以通過命名空間.類名，實現調用

層中Imports引用：直接寫調用的類名即可

3、實例化對象與定義同類型變量區別

newUserEn()是指在內存中開辟了一塊空間，創建了一個對象，然后讓一個UserEn類型的變量user引用(指向)它。user也只不過是創建的那個實體對象的名稱而已。

?

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