１.三層之間的關系：

三層是指：界面顯示層(UI)，業務邏輯層(Business)，數據操作層(Data Access)

文字描述：

Clients對UI進行操作，UI調用Business進行相應的運算和處理，Business通過Data Access對Data Base進行操作。

?優點：

1、增加了代碼的重用。Data Access可在多個項目中公用；Business可在同一項目的不同地方使用（如某個軟件B/S和C/S部分可以共用一系列的Business組件）。

2、使得軟件的分層更加明晰，便于開發和維護。美工人員可以很方便地設計UI設計，并在其中調用Business給出的接口，而程序開發人員則可以專注的進行代碼的編寫和功能的實現。

?

２.Data Access的具體實現：

DataAgent類型中變量和方法的說明：

?

private string m_strConnectionString; //連接字符串

private OleDbConnection m_objConnection; //數據庫連接

?

public DataAgent(string strConnection) //構造方法，傳入的參數為連接字符串

private void OpenDataBase() //打開數據庫連接

private void #region CloseDataBase() //關閉數據庫連接

public DataView GetDataView(string strSqlStat) //根據傳入的連接字符串返回DataView

?

具體實現代碼如下：

?

Code
??1public?class?DataAgent
??2
??3?????{
??4
??5?
??6
??7?????????Variables#region?Variables
??8
??9?
?10
?11?????????private?string?m_strConnectionString;
?12
?13?????????private?OleDbConnection?m_objConnection;
?14
?15?
?16
?17?????????#endregion?Variables
?18
?19?
?20
?21?????????Functions#region?Functions
?22
?23?
?24
?25?????????DataAgend#region?DataAgend
?26
?27?????????/**////?<summary>
?28
?29?????????///?Initial?Function
?30
?31?????????///?</summary>
?32
?33?????????///?<param?name="strConnection"></param>
?34
?35?????????public?DataAgent(string?strConnection)
?36
?37?????????{
?38
?39??????????????this.m_strConnectionString?=?strConnection;
?40
?41?????????}
?42
?43?????????#endregion?DataAgend
?44
?45?
?46
?47?????????OpenDataBase#region?OpenDataBase
?48
?49?????????/**////?<summary>
?50
?51?????????///?function?to?open?data?base
?52
?53?????????///?</summary>
?54
?55?????????private?void?OpenDataBase()
?56
?57?????????{
?58
?59??????????????try
?60
?61??????????????{
?62
?63???????????????????this.m_objConnection?=?new?OleDbConnection();
?64
?65???????????????????this.m_objConnection.ConnectionString?=?this.m_strConnectionString;
?66
?67?
?68
?69???????????????????if(this.m_objConnection.State?!=?ConnectionState.Open)
?70
?71???????????????????{
?72
?73???????????????????????this.m_objConnection.Open();
?74
?75???????????????????}
?76
?77??????????????}
?78
?79??????????????catch(Exception?e)
?80
?81??????????????{
?82
?83???????????????????throw?e;
?84
?85??????????????}
?86
?87?????????}
?88
?89?????????#endregion?OpenDataBase
?90
?91?
?92
?93?????????CloseDataBase#region?CloseDataBase
?94
?95?????????/**////?<summary>
?96
?97?????????///?the?function?to?cloase?data?base
?98
?99?????????///?</summary>
100
101?????????private?void?CloseDataBase()
102
103?????????{
104
105??????????????if(this.m_objConnection?!=?null)
106
107??????????????{
108
109???????????????????if(this.m_objConnection.State?==?ConnectionState.Open)
110
111???????????????????{
112
113????????????????????????this.m_objConnection.Close();
114
115???????????????????}
116
117??????????????}
118
119?????????}
120
121?????????#endregion
122
123?
124
125?????????GetDataView#region?GetDataView
126
127?????????/**////?<summary>
128
129?????????///?Execute?the?sql?and?return?the?default?table?view
130
131?????????///?</summary>
132
133?????????///?<param?name="strSelectString">Select?String</param>
134
135?????????///?<returns>DataView?of?the?DataTable</returns>
136
137?????????public?DataView?GetDataView(string?strSqlStat)
138
139?????????{
140
141??????????????try
142
143??????????????{
144
145???????????????????this.OpenDataBase();
146
147???????????????????OleDbDataAdapter?objDataAdapter?=?new?OleDbDataAdapter(strSqlStat.Trim(),this.m_objConnection);
148
149???????????????????DataSet?objDataSet?=?new?DataSet();
150
151??????????????????objDataAdapter.Fill(objDataSet);
152
153???????????????????return?objDataSet.Tables[0].DefaultView;
154
155??????????????}
156
157??????????????catch(Exception?e)
158
159??????????????{
160
161???????????????????throw?e;
162
163??????????????}
164
165??????????????finally
166
167??????????????{
168
169???????????????????this.CloseDataBase();
170
171??????????????}
172
173?????????}
174
175?????????#endregion?GetDataTable
176
177?????????#endregion?Functions
178
179?
180
181?????}

３.Business的具體實現：

建立名為Base的類，此類作為其他事務類的基類，其中定義了一個DataAgent的實例。其他所有的Business類都從該改類派生。

在該類中添加對DataAgent的引用，使所有的事務類都能使用DataAgent中的方法。

?

Base.cs源代碼：

?

Code
?1???public?abstract?class?Base
?2
?3?????{
?4
?5?????????DataAgent#region?DataAgent
?6
?7?????????private?DataAgent?m_objDBAgent;
?8
?9?
10
11?????????protected?DataAgent?OleDBAgent
12
13?????????{
14
15??????????????get
16
17??????????????{
18
19???????????????????if(this.m_objDBAgent?==?null)
20
21???????????????????{
22
23???????????????????????this.m_objDBAgent?=?this.CreateAgent();
24
25???????????????????}
26
27???????????????????return?this.m_objDBAgent;
28
29??????????????}
30
31??????????????set
32
33??????????????{
34
35???????????????????this.m_objDBAgent?=?value;
36
37??????????????}
38
39?????????}
40
41?????????#endregion?DataAgent
42
43?
44
45?????????public?Base()
46
47?????????{
48
49?????????}
50
51?
52
53?????????CreateAgent#region?CreateAgent
54
55?????????/**////?<summary>
56
57?????????///?Create?a?new?DataAgent
58
59?????????///?</summary>
60
61?????????///?<returns>the?DataAgent</returns>
62
63?????????private?DataAgent?CreateAgent()
64
65?????????{
66
67??????????????string?strConnection?=?ConfigurationSettings.AppSettings["ConnectionString"];
68
69??????????????return?new?DataAgent(strConnection);
70
71??????????}
72
73?????????#endregion?CreateAgent
74
75????}

?

???? 準備好了數據操作層和事務層的基類，底下就可以正式地開始業務邏輯類的開發了，如有一個顯示新聞的類News,其中包含了一個GetNewsLsit()的方法，該方法用來獲取所有的新聞標題列表，代碼如下：

?

Code
?1public?class?News:?Base
?2
?3?????{
?4
?5?????????public?News?Contact()
?6
?7?????????{
?8
?9?
10
11?????????}
12
13?
14
15?????????public?DataView?GetNewsList()
16
17?????????{
18
19??????????????string?strSql;
20
21??????????????strSql?=?"";
22
23??????????????strSql?+=?"???SELECT?Top?10?NewsId,NewsTitle?";
24
25??????????????strSql?+=?"?????FROM?Tb_News";
26
27??????????????strSql?+=?"????WHERE?NewsEnable?=?1";
28
29??????????????strSql?+=?"?ORDER?BY?NewsId?";
30
31?
32
33??????????????return?base.OleDBAgent.GetDataView(strSql);
34
35?
36
37?????????}
38
39?????}

?

?

由于數據庫結構比較簡單，在此就不再給出詳細的表結構。

?

４.UI層對Business中接口的調用

首先，在頁面中添加對News類的引用。

然后，在頁面中添加一個(DataGrid)dgNews用來顯示新聞列表。

在Page Behind的Page_Load方法中添加如下代碼：

　　

1??News?objNews?=?new?News();
2
3?????????this.dgNews.DataSource?=?objNews.GetNewsList();
4
5????this.dgNews.DataBind();

?

?

?

Code
?1?public?abstract?class?Base
?2
?3?????{
?4
?5?????????DataAgent#region?DataAgent
?6
?7?????????private?DataAgent?m_objDBAgent;
?8
?9?
10
11?????????protected?DataAgent?OleDBAgent
12
13?????????{
14
15??????????????get
16
17??????????????{
18
19???????????????????if(this.m_objDBAgent?==?null)
20
21???????????????????{
22
23???????????????????????this.m_objDBAgent?=?this.CreateAgent();
24
25???????????????????}
26
27???????????????????return?this.m_objDBAgent;
28
29??????????????}
30
31??????????????set
32
33??????????????{
34
35???????????????????this.m_objDBAgent?=?value;
36
37??????????????}
38
39?????????}
40
41?????????#endregion?DataAgent
42
43?
44
45?????????public?Base()
46
47?????????{
48
49?????????}
50
51?
52
53?????????CreateAgent#region?CreateAgent
54
55?????????/**////?<summary>
56
57?????????///?Create?a?new?DataAgent
58
59?????????///?</summary>
60
61?????????///?<returns>the?DataAgent</returns>
62
63?????????private?DataAgent?CreateAgent()
64
65?????????{
66
67??????????????string?strConnection?=?ConfigurationSettings.AppSettings["ConnectionString"];
68
69??????????????return?new?DataAgent(strConnection);
70
71??????????}
72
73?????????#endregion?CreateAgent
74
75????}

轉載于:https://www.cnblogs.com/KivenSun/articles/1434368.html

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