状态模式(State Pattern)

偏执的太偏执、 2022-03-31 11:40 243阅读 0赞

### [设计模式 - 吕震宇][-]  [.NET设计模式系列文章][.NET]  [薛敬明的专栏][Link 1]     [乐在其中设计模式(C\#)][C] ###

### [设计模式24：State Pattern (状态模式)][24_State Pattern] ###

英文原文：[http://www.dofactory.com/Patterns/PatternState.aspx][http_www.dofactory.com_Patterns_PatternState.aspx]

### 一、State Pattern (状态模式) ###

Define: Allow an object to alter its behavior when its internal state changes. The object will appear to change its class.

定义：当一个对象的内部状态进行改变的时候允许对象改变其行为。这个对象将显然可以改变其类。

### 二、UML类图 ###

![state][]

*  **Context** **(Account)**
    
     *  defines the interface of interest to clients
     *  maintains an instance of a ConcreteState subclass that defines the current state.
 *  **State** **(State)**
    
     *  defines an interface for encapsulating the behavior associated with a particular state of the Context.
 *  **Concrete State** **(RedState, SilverState, GoldState)**
    
     *  each subclass implements a behavior associated with a state of Context
    
    ### 三、State Pattern (状态模式)实例性代码 ###
    
    **\[c-sharp\]** [ view plain][view plain] [copy][view plain]
    
    1.  using System;
    2.  using System.Collections.Generic;
    3.  using System.Linq;
    4.  using System.Text;
    5.  
    6.  namespace State\_Pattern
    7.  \{
    8.  /// <summary>
    9.  
    10. /// MainApp startup class for Structural
    11. 
    12. /// State Design Pattern.
    13. 
    14. /// </summary>
    15. 
    16. class MainApp
    17. \{
    18. 
    19. /// <summary>
    20. 
    21. /// Entry point into console application.
    22. 
    23. /// </summary>
    24. 
    25. static void Main()
    26. \{
    27. 
    28. // Setup context in a state
    29. 
    30. Context c = new Context(new ConcreteStateA());
    31. 
    32. 
    33. 
    34. // Issue requests, which toggles state
    35. 
    36. c.Request();
    37. 
    38. c.Request();
    39. 
    40. c.Request();
    41. 
    42. c.Request();
    43. 
    44. 
    45. 
    46. // Wait for user
    47. 
    48. Console.ReadKey();
    49. 
    50. \}
    51. 
    52. \}
    53. 
    54. 
    55. 
    56. /// <summary>
    57. 
    58. /// The 'State' abstract class
    59. 
    60. /// </summary>
    61. 
    62. abstract class State
    63. \{
    64. 
    65. public abstract void Handle(Context context);
    66. 
    67. \}
    68. 
    69. 
    70. 
    71. /// <summary>
    72. 
    73. /// A 'ConcreteState' class
    74. 
    75. /// </summary>
    76. 
    77. class ConcreteStateA : State
    78. \{
    79. 
    80. public override void Handle(Context context)
    81. \{
    82. 
    83. context.State = new ConcreteStateB();
    84. 
    85. \}
    86. 
    87. \}
    88. 
    89. 
    90. 
    91. /// <summary>
    92. 
    93. /// A 'ConcreteState' class
    94. 
    95. /// </summary>
    96. 
    97. class ConcreteStateB : State
    98. \{
    99. 
    100. public override void Handle(Context context)
    101. \{
    102. 
    103. context.State = new ConcreteStateA();
    104. 
    105. \}
    106. 
    107. \}
    108. 
    109. 
    110. 
    111. /// <summary>
    112. 
    113. /// The 'Context' class
    114. 
    115. /// </summary>
    116. 
    117. class Context
    118. \{
    119. 
    120. private State \_state;
    121. 
    122. 
    123. 
    124. // Constructor
    125. 
    126. public Context(State state)
    127. \{
    128. 
    129. this.State = state;
    130. 
    131. \}
    132. 
    133. 
    134. 
    135. // Gets or sets the state
    136. 
    137. public State State
    138. \{
    139. 
    140. get \{ return \_state; \}
    141. 
    142. set
    143. \{
    144. 
    145. \_state = value;
    146. 
    147. Console.WriteLine("State: " \+
    148. 
    149. \_state.GetType().Name);
    150. 
    151. \}
    152. 
    153. \}
    154. 
    155. 
    156. 
    157. public void Request()
    158. \{
    159. 
    160. \_state.Handle(this);
    161. 
    162. \}
    163. 
    164. \}
    165. \}
    
    ### 四、使用State Pattern (状态模式)的实例代码 ###
    
    This real-world code demonstrates the State pattern which allows an Account to behave differently depending on its balance. The difference in behavior is delegated to State objects called RedState, SilverState and GoldState. These states represent overdrawn accounts, starter accounts, and accounts in good standing.
    
    **\[c-sharp\]** [ view plain][view plain] [copy][view plain]
    
    1.  using System;
    2.  using System.Collections.Generic;
    3.  using System.Linq;
    4.  using System.Text;
    5.  
    6.  namespace State\_Pattern
    7.  \{
    8.  /// <summary>
    9.  
    10. /// MainApp startup class for Real-World 
    11. 
    12. /// State Design Pattern.
    13. 
    14. /// </summary>
    15. 
    16. class MainApp
    17. \{
    18. 
    19. /// <summary>
    20. 
    21. /// Entry point into console application.
    22. 
    23. /// </summary>
    24. 
    25. static void Main()
    26. \{
    27. 
    28. // Open a new account
    29. 
    30. Account account = new Account("Jim Johnson");
    31. 
    32. 
    33. 
    34. // Apply financial transactions
    35. 
    36. account.Deposit(500.0);
    37. 
    38. account.Deposit(300.0);
    39. 
    40. account.Deposit(550.0);
    41. 
    42. account.PayInterest();
    43. 
    44. account.Withdraw(2000.00);
    45. 
    46. account.Withdraw(1100.00);
    47. 
    48. 
    49. 
    50. // Wait for user
    51. 
    52. Console.ReadKey();
    53. 
    54. \}
    55. 
    56. \}
    57. 
    58. 
    59. 
    60. /// <summary>
    61. 
    62. /// The 'State' abstract class
    63. 
    64. /// </summary>
    65. 
    66. abstract class State
    67. \{
    68. 
    69. protected Account account;
    70. 
    71. protected double balance;
    72. 
    73. 
    74. 
    75. protected double interest;
    76. 
    77. protected double lowerLimit;
    78. 
    79. protected double upperLimit;
    80. 
    81. 
    82. 
    83. // Properties
    84. 
    85. public Account Account
    86. \{
    87. 
    88. get \{ return account; \}
    89. 
    90. set \{ account = value; \}
    91. 
    92. \}
    93. 
    94. 
    95. 
    96. public double Balance
    97. \{
    98. 
    99. get \{ return balance; \}
    100. 
    101. set \{ balance = value; \}
    102. 
    103. \}
    104. 
    105. 
    106. 
    107. public abstract void Deposit(double amount);
    108. 
    109. public abstract void Withdraw(double amount);
    110. 
    111. public abstract void PayInterest();
    112. 
    113. \}
    114. 
    115. 
    116. 
    117. 
    118. 
    119. /// <summary>
    120. 
    121. /// A 'ConcreteState' class
    122. 
    123. /// <remarks>
    124. 
    125. /// Red indicates that account is overdrawn 
    126. 
    127. /// </remarks>
    128. 
    129. /// </summary>
    130. 
    131. class RedState : State
    132. \{
    133. 
    134. private double \_serviceFee;
    135. 
    136. 
    137. 
    138. // Constructor
    139. 
    140. public RedState(State state)
    141. \{
    142. 
    143. this.balance = state.Balance;
    144. 
    145. this.account = state.Account;
    146. 
    147. Initialize();
    148. 
    149. \}
    150. 
    151. 
    152. 
    153. private void Initialize()
    154. \{
    155. 
    156. // Should come from a datasource
    157. 
    158. interest = 0.0;
    159. 
    160. lowerLimit = -100.0;
    161. 
    162. upperLimit = 0.0;
    163. 
    164. \_serviceFee = 15.00;
    165. 
    166. \}
    167. 
    168. 
    169. 
    170. public override void Deposit(double amount)
    171. \{
    172. 
    173. balance += amount;
    174. 
    175. StateChangeCheck();
    176. 
    177. \}
    178. 
    179. 
    180. 
    181. public override void Withdraw(double amount)
    182. \{
    183. 
    184. amount = amount - \_serviceFee;
    185. 
    186. Console.WriteLine("No funds available for withdrawal!");
    187. 
    188. \}
    189. 
    190. 
    191. 
    192. public override void PayInterest()
    193. \{
    194. 
    195. // No interest is paid
    196. 
    197. \}
    198. 
    199. 
    200. 
    201. private void StateChangeCheck()
    202. \{
    203. 
    204. if (balance > upperLimit)
    205. \{
    206. 
    207. account.State = new SilverState(this);
    208. 
    209. \}
    210. 
    211. \}
    212. 
    213. \}
    214. 
    215. 
    216. 
    217. /// <summary>
    218. 
    219. /// A 'ConcreteState' class
    220. 
    221. /// <remarks>
    222. 
    223. /// Silver indicates a non-interest bearing state
    224. 
    225. /// </remarks>
    226. 
    227. /// </summary>
    228. 
    229. class SilverState : State
    230. \{
    231. 
    232. // Overloaded constructors
    233. 
    234. 
    235. 
    236. public SilverState(State state) :
    237. 
    238. this(state.Balance, state.Account)
    239. \{
    240. 
    241. \}
    242. 
    243. 
    244. 
    245. public SilverState(double balance, Account account)
    246. \{
    247. 
    248. this.balance = balance;
    249. 
    250. this.account = account;
    251. 
    252. Initialize();
    253. 
    254. \}
    255. 
    256. 
    257. 
    258. private void Initialize()
    259. \{
    260. 
    261. // Should come from a datasource
    262. 
    263. interest = 0.0;
    264. 
    265. lowerLimit = 0.0;
    266. 
    267. upperLimit = 1000.0;
    268. 
    269. \}
    270. 
    271. 
    272. 
    273. public override void Deposit(double amount)
    274. \{
    275. 
    276. balance += amount;
    277. 
    278. StateChangeCheck();
    279. 
    280. \}
    281. 
    282. 
    283. 
    284. public override void Withdraw(double amount)
    285. \{
    286. 
    287. balance -= amount;
    288. 
    289. StateChangeCheck();
    290. 
    291. \}
    292. 
    293. 
    294. 
    295. public override void PayInterest()
    296. \{
    297. 
    298. balance += interest \* balance;
    299. 
    300. StateChangeCheck();
    301. 
    302. \}
    303. 
    304. 
    305. 
    306. private void StateChangeCheck()
    307. \{
    308. 
    309. if (balance < lowerLimit)
    310. \{
    311. 
    312. account.State = new RedState(this);
    313. 
    314. \}
    315. 
    316. else if (balance > upperLimit)
    317. \{
    318. 
    319. account.State = new GoldState(this);
    320. 
    321. \}
    322. 
    323. \}
    324. 
    325. \}
    326. 
    327. 
    328. 
    329. /// <summary>
    330. 
    331. /// A 'ConcreteState' class
    332. 
    333. /// <remarks>
    334. 
    335. /// Gold indicates an interest bearing state
    336. 
    337. /// </remarks>
    338. 
    339. /// </summary>
    340. 
    341. class GoldState : State
    342. \{
    343. 
    344. // Overloaded constructors
    345. 
    346. public GoldState(State state)
    347. 
    348. : this(state.Balance, state.Account)
    349. \{
    350. 
    351. \}
    352. 
    353. 
    354. 
    355. public GoldState(double balance, Account account)
    356. \{
    357. 
    358. this.balance = balance;
    359. 
    360. this.account = account;
    361. 
    362. Initialize();
    363. 
    364. \}
    365. 
    366. 
    367. 
    368. private void Initialize()
    369. \{
    370. 
    371. // Should come from a database
    372. 
    373. interest = 0.05;
    374. 
    375. lowerLimit = 1000.0;
    376. 
    377. upperLimit = 10000000.0;
    378. 
    379. \}
    380. 
    381. 
    382. 
    383. public override void Deposit(double amount)
    384. \{
    385. 
    386. balance += amount;
    387. 
    388. StateChangeCheck();
    389. 
    390. \}
    391. 
    392. 
    393. 
    394. public override void Withdraw(double amount)
    395. \{
    396. 
    397. balance -= amount;
    398. 
    399. StateChangeCheck();
    400. 
    401. \}
    402. 
    403. 
    404. 
    405. public override void PayInterest()
    406. \{
    407. 
    408. balance += interest \* balance;
    409. 
    410. StateChangeCheck();
    411. 
    412. \}
    413. 
    414. 
    415. 
    416. private void StateChangeCheck()
    417. \{
    418. 
    419. if (balance < 0.0)
    420. \{
    421. 
    422. account.State = new RedState(this);
    423. 
    424. \}
    425. 
    426. else if (balance < lowerLimit)
    427. \{
    428. 
    429. account.State = new SilverState(this);
    430. 
    431. \}
    432. 
    433. \}
    434. 
    435. \}
    436. 
    437. 
    438. 
    439. /// <summary>
    440. 
    441. /// The 'Context' class
    442. 
    443. /// </summary>
    444. 
    445. class Account
    446. \{
    447. 
    448. private State \_state;
    449. 
    450. private string \_owner;
    451. 
    452. 
    453. 
    454. // Constructor
    455. 
    456. public Account(string owner)
    457. \{
    458. 
    459. // New accounts are 'Silver' by default
    460. 
    461. this.\_owner = owner;
    462. 
    463. this.\_state = new SilverState(0.0, this);
    464. 
    465. \}
    466. 
    467. 
    468. 
    469. // Properties
    470. 
    471. public double Balance
    472. \{
    473. 
    474. get \{ return \_state.Balance; \}
    475. 
    476. \}
    477. 
    478. 
    479. 
    480. public State State
    481. \{
    482. 
    483. get \{ return \_state; \}
    484. 
    485. set \{ \_state = value; \}
    486. 
    487. \}
    488. 
    489. 
    490. 
    491. public void Deposit(double amount)
    492. \{
    493. 
    494. \_state.Deposit(amount);
    495. 
    496. Console.WriteLine("Deposited \{0:C\} --- ", amount);
    497. 
    498. Console.WriteLine(" Balance = \{0:C\}", this.Balance);
    499. 
    500. Console.WriteLine(" Status = \{0\}",
    501. 
    502. this.State.GetType().Name);
    503. 
    504. Console.WriteLine("");
    505. 
    506. \}
    507. 
    508. 
    509. 
    510. public void Withdraw(double amount)
    511. \{
    512. 
    513. \_state.Withdraw(amount);
    514. 
    515. Console.WriteLine("Withdrew \{0:C\} --- ", amount);
    516. 
    517. Console.WriteLine(" Balance = \{0:C\}", this.Balance);
    518. 
    519. Console.WriteLine(" Status = \{0\}/n",
    520. 
    521. this.State.GetType().Name);
    522. 
    523. \}
    524. 
    525. 
    526. 
    527. public void PayInterest()
    528. \{
    529. 
    530. \_state.PayInterest();
    531. 
    532. Console.WriteLine("Interest Paid --- ");
    533. 
    534. Console.WriteLine(" Balance = \{0:C\}", this.Balance);
    535. 
    536. Console.WriteLine(" Status = \{0\}/n",
    537. 
    538. this.State.GetType().Name);
    539. 
    540. \}
    541. 
    542. \}
    543. \}
    
      
    
    
    # 乐在其中设计模式(C\#) - 状态模式(State Pattern) #
    
    介绍  
    允许一个对象在其内部状态改变时改变它的行为。对象看起来似乎修改了它所属的类。  
      
      
    示例  
    有一个Message实体类，对它的操作有Insert()和Get()方法，持久化数据在SqlServer数据库中或Xml文件里。在对象内部可以根据用户的不同选择不同的数据持久化方案。  
    ![o_State.png][]  
      
      
    MessageModel  
    
    
    ![None.gif][] using  System;  
    ![None.gif][] using  System.Collections.Generic;  
    ![None.gif][] using  System.Text;  
    ![None.gif][]  
    ![None.gif][] namespace  Pattern.State  
    ![ExpandedBlockStart.gif][] \{  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// Message实体类  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![InBlock.gif][]publicclass MessageModel  
    ![ExpandedSubBlockStart.gif][]\{  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 构造函数  
    ![InBlock.gif][]///</summary>  
    ![InBlock.gif][]///<param name="msg">Message内容</param>  
    ![ExpandedSubBlockEnd.gif][]///<param name="pt">Message发布时间</param>  
    ![InBlock.gif][]public MessageModel(string msg, DateTime pt)  
    ![ExpandedSubBlockStart.gif][]\{  
    ![InBlock.gif][]this.\_message = msg;  
    ![InBlock.gif][]this.\_publishTime = pt;  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![InBlock.gif][]  
    ![InBlock.gif][]privatestring \_message;  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// Message内容  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![InBlock.gif][]publicstring Message  
    ![ExpandedSubBlockStart.gif][]\{  
    ![ExpandedSubBlockStart.gif][]get\{ return \_message; \}  
    ![ExpandedSubBlockStart.gif][]set\{ \_message = value; \}  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![InBlock.gif][]  
    ![InBlock.gif][]private DateTime \_publishTime;  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// Message发布时间  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![InBlock.gif][]public DateTime PublishTime  
    ![ExpandedSubBlockStart.gif][]\{  
    ![ExpandedSubBlockStart.gif][]get\{ return \_publishTime; \}  
    ![ExpandedSubBlockStart.gif][]set\{ \_publishTime = value; \}  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![ExpandedBlockEnd.gif][]\}   
    ![None.gif][]
    
      
    AbstractMessageState  
    
    
    ![None.gif][] using  System;  
    ![None.gif][] using  System.Collections.Generic;  
    ![None.gif][] using  System.Text;  
    ![None.gif][]  
    ![None.gif][] namespace  Pattern.State  
    ![ExpandedBlockStart.gif][] \{  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 状态模式抽象类  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![InBlock.gif][]publicabstractclass AbstractMessageState  
    ![ExpandedSubBlockStart.gif][]\{  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// Context类型  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![InBlock.gif][]protected Message \_message;  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// Context类型属性  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![InBlock.gif][]public Message Message  
    ![ExpandedSubBlockStart.gif][]\{  
    ![ExpandedSubBlockStart.gif][]get\{ return \_message; \}  
    ![ExpandedSubBlockStart.gif][]set\{ \_message = value; \}  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 改变状态  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![InBlock.gif][]publicabstractvoid StateChangeCheck();  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 获取Message  
    ![InBlock.gif][]///</summary>  
    ![ExpandedSubBlockEnd.gif][]///<returns></returns>  
    ![InBlock.gif][]publicabstract List<MessageModel> Get();  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 插入Message  
    ![InBlock.gif][]///</summary>  
    ![InBlock.gif][]///<param name="mm">Message实体对象</param>  
    ![ExpandedSubBlockEnd.gif][]///<returns></returns>  
    ![InBlock.gif][]publicabstractbool Insert(MessageModel mm);  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![ExpandedBlockEnd.gif][]\}   
    ![None.gif][]
    
      
    XmlMessage  
    
    
    ![None.gif][] using  System;  
    ![None.gif][] using  System.Collections.Generic;  
    ![None.gif][] using  System.Text;  
    ![None.gif][]  
    ![None.gif][] namespace  Pattern.State  
    ![ExpandedBlockStart.gif][] \{  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// Xml方式操作Message  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![InBlock.gif][]publicclass XmlMessage : AbstractMessageState  
    ![ExpandedSubBlockStart.gif][]\{  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 构造函数  
    ![InBlock.gif][]///</summary>  
    ![ExpandedSubBlockEnd.gif][]///<param name="message">Context类型参数</param>  
    ![InBlock.gif][]public XmlMessage(Message message)  
    ![ExpandedSubBlockStart.gif][]\{  
    ![InBlock.gif][]this.\_message = message;  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 改变状态  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![InBlock.gif][]publicoverridevoid StateChangeCheck()  
    ![ExpandedSubBlockStart.gif][]\{  
    ![InBlock.gif][]// 如果UserId是admin则变换状态为SqlMessage  
    ![InBlock.gif][]if (this.\_message.UserId =="admin")  
    ![ExpandedSubBlockStart.gif][]\{  
    ![InBlock.gif][]this.\_message.AbstractMessageState =new SqlMessage(this.\_message);  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 获取Message  
    ![InBlock.gif][]///</summary>  
    ![ExpandedSubBlockEnd.gif][]///<returns></returns>  
    ![InBlock.gif][]publicoverride List<MessageModel> Get()  
    ![ExpandedSubBlockStart.gif][]\{  
    ![InBlock.gif][] List<MessageModel> l =new List<MessageModel>();  
    ![InBlock.gif][] l.Add(new MessageModel("XML方式获取Message", DateTime.Now));  
    ![InBlock.gif][]  
    ![InBlock.gif][]return l;  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 插入Message  
    ![InBlock.gif][]///</summary>  
    ![InBlock.gif][]///<param name="mm">Message实体对象</param>  
    ![ExpandedSubBlockEnd.gif][]///<returns></returns>  
    ![InBlock.gif][]publicoverridebool Insert(MessageModel mm)  
    ![ExpandedSubBlockStart.gif][]\{  
    ![InBlock.gif][]// 代码略  
    ![InBlock.gif][]returntrue;  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![ExpandedBlockEnd.gif][]\}   
    ![None.gif][]
    
      
    SqlMessage  
    
    
    ![None.gif][] using  System;  
    ![None.gif][] using  System.Collections.Generic;  
    ![None.gif][] using  System.Text;  
    ![None.gif][]  
    ![None.gif][] namespace  Pattern.State  
    ![ExpandedBlockStart.gif][] \{  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// Sql方式操作Message  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![InBlock.gif][]publicclass SqlMessage : AbstractMessageState  
    ![ExpandedSubBlockStart.gif][]\{  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 构造函数  
    ![InBlock.gif][]///</summary>  
    ![ExpandedSubBlockEnd.gif][]///<param name="message">Context类型参数</param>  
    ![InBlock.gif][]public SqlMessage(Message message)  
    ![ExpandedSubBlockStart.gif][]\{  
    ![InBlock.gif][]this.\_message = message;  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 改变状态  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![InBlock.gif][]publicoverridevoid StateChangeCheck()  
    ![ExpandedSubBlockStart.gif][]\{  
    ![InBlock.gif][]  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 获取Message  
    ![InBlock.gif][]///</summary>  
    ![ExpandedSubBlockEnd.gif][]///<returns></returns>  
    ![InBlock.gif][]publicoverride List<MessageModel> Get()  
    ![ExpandedSubBlockStart.gif][]\{  
    ![InBlock.gif][] List<MessageModel> l =new List<MessageModel>();  
    ![InBlock.gif][] l.Add(new MessageModel("SQL方式获取Message", DateTime.Now));  
    ![InBlock.gif][]  
    ![InBlock.gif][]return l;  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 插入Message  
    ![InBlock.gif][]///</summary>  
    ![InBlock.gif][]///<param name="mm">Message实体对象</param>  
    ![ExpandedSubBlockEnd.gif][]///<returns></returns>  
    ![InBlock.gif][]publicoverridebool Insert(MessageModel mm)  
    ![ExpandedSubBlockStart.gif][]\{  
    ![InBlock.gif][]// 代码略  
    ![InBlock.gif][]returntrue;  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![ExpandedBlockEnd.gif][]\}   
    ![None.gif][]
    
      
    Message  
    
    
    ![None.gif][] using  System;  
    ![None.gif][] using  System.Collections.Generic;  
    ![None.gif][] using  System.Text;  
    ![None.gif][]  
    ![None.gif][] namespace  Pattern.State  
    ![ExpandedBlockStart.gif][] \{  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// Context类  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![InBlock.gif][]publicclass Message  
    ![ExpandedSubBlockStart.gif][]\{  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 类型为状态模式抽象类的私有变量  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![InBlock.gif][]private AbstractMessageState \_abstractMessageState;  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 类型为状态模式抽象类的属性  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![InBlock.gif][]public AbstractMessageState AbstractMessageState  
    ![ExpandedSubBlockStart.gif][]\{  
    ![ExpandedSubBlockStart.gif][]get\{ return \_abstractMessageState; \}  
    ![ExpandedSubBlockStart.gif][]set\{ \_abstractMessageState = value; \}  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// UserId私有变量  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![InBlock.gif][]privatestring \_userId;  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// UserId  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![InBlock.gif][]publicstring UserId  
    ![ExpandedSubBlockStart.gif][]\{  
    ![ExpandedSubBlockStart.gif][]get\{ return \_userId; \}  
    ![ExpandedSubBlockStart.gif][]set\{ \_userId = value; \}  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 构造函数  
    ![InBlock.gif][]///</summary>  
    ![ExpandedSubBlockEnd.gif][]///<param name="userId">UserId</param>  
    ![InBlock.gif][]public Message(string userId)  
    ![ExpandedSubBlockStart.gif][]\{  
    ![InBlock.gif][]this.\_userId = userId;  
    ![InBlock.gif][]  
    ![InBlock.gif][] \_abstractMessageState =new XmlMessage(this);  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 获取Message  
    ![InBlock.gif][]///</summary>  
    ![ExpandedSubBlockEnd.gif][]///<returns></returns>  
    ![InBlock.gif][]public List<MessageModel> Get()  
    ![ExpandedSubBlockStart.gif][]\{  
    ![InBlock.gif][]// 修改状态  
    ![InBlock.gif][] \_abstractMessageState.StateChangeCheck();  
    ![InBlock.gif][]  
    ![InBlock.gif][]return \_abstractMessageState.Get();  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 插入Message  
    ![InBlock.gif][]///</summary>  
    ![InBlock.gif][]///<param name="mm">Message实体对象</param>  
    ![ExpandedSubBlockEnd.gif][]///<returns></returns>  
    ![InBlock.gif][]publicbool Insert(MessageModel mm)  
    ![ExpandedSubBlockStart.gif][]\{  
    ![InBlock.gif][]// 修改状态  
    ![InBlock.gif][] \_abstractMessageState.StateChangeCheck();  
    ![InBlock.gif][]  
    ![InBlock.gif][]return \_abstractMessageState.Insert(mm);  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![ExpandedBlockEnd.gif][]\}   
    ![None.gif][]
    
      
      
    client  
    
    
    ![None.gif][] using  System;  
    ![None.gif][] using  System.Data;  
    ![None.gif][] using  System.Configuration;  
    ![None.gif][] using  System.Collections;  
    ![None.gif][] using  System.Web;  
    ![None.gif][] using  System.Web.Security;  
    ![None.gif][] using  System.Web.UI;  
    ![None.gif][] using  System.Web.UI.WebControls;  
    ![None.gif][] using  System.Web.UI.WebControls.WebParts;  
    ![None.gif][] using  System.Web.UI.HtmlControls;  
    ![None.gif][]  
    ![None.gif][] using  Pattern.State;  
    ![None.gif][]  
    ![None.gif][] public  partial  class  State : System.Web.UI.Page  
    ![ExpandedBlockStart.gif][] \{  
    ![InBlock.gif][]protectedvoid Page\_Load(object sender, EventArgs e)  
    ![ExpandedSubBlockStart.gif][]\{  
    ![InBlock.gif][] Message m =new Message("admin");  
    ![InBlock.gif][] Response.Write(m.Insert(new MessageModel("插入", DateTime.Now)));  
    ![InBlock.gif][] Response.Write("<br />");  
    ![InBlock.gif][] Response.Write(m.Get()\[0\].Message \+""\+ m.Get()\[0\].PublishTime.ToString());  
    ![InBlock.gif][] Response.Write("<br />");  
    ![InBlock.gif][]  
    ![InBlock.gif][] m =new Message("user");  
    ![InBlock.gif][] Response.Write(m.Insert(new MessageModel("插入", DateTime.Now)));  
    ![InBlock.gif][] Response.Write("<br />");  
    ![InBlock.gif][] Response.Write(m.Get()\[0\].Message \+""\+ m.Get()\[0\].PublishTime.ToString());  
    ![InBlock.gif][] Response.Write("<br />");  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![ExpandedBlockEnd.gif][]\}   
    ![None.gif][]
    
      
    运行结果  
    True  
    SQL方式获取Message 2007-3-6 22:58:17  
    True  
    XML方式获取Message 2007-3-6 22:58:17  
      
      
    参考  
    [http://www.dofactory.com/Patterns/PatternState.aspx][http_www.dofactory.com_Patterns_PatternState.aspx]  
      
      
    OK  
    [\[源码下载\]][Link 2]

[-]: http://www.cnblogs.com/zhenyulu/category/6930.html
[.NET]: http://www.cnblogs.com/Terrylee/archive/2006/07/17/334911.html
[Link 1]: http://blog.csdn.net/rocket5725/article/category/559017
[C]: http://www.cnblogs.com/webabcd/category/82668.html
[24_State Pattern]: http://blog.csdn.net/rocket5725/article/details/4334329
[http_www.dofactory.com_Patterns_PatternState.aspx]: http://www.dofactory.com/Patterns/PatternState.aspx
[state]: /images/20220331/3bee3ff81ec440c4bffd1310fe1123b1.png
[view plain]: http://blog.csdn.net/rocket5725/article/details/4334329#
[o_State.png]: /images/20220331/f7ed1ecddf76417e851aaa4eccef520b.png
[None.gif]: /images/20220331/2864d99bdc5f4547add4af817c32837c.png
[ExpandedBlockStart.gif]: /images/20220331/93b0d3577a664cd78663a864c026e8d7.png
[ExpandedSubBlockStart.gif]: /images/20220331/2c99c9aeb2614dff8807c27f1496c61a.png
[InBlock.gif]: /images/20220331/eb44158c49c74f9c8404e7d619213bc8.png
[ExpandedSubBlockEnd.gif]: /images/20220331/0cf4d824283648bfb46651b5602a5863.png
[ExpandedBlockEnd.gif]: /images/20220331/59444cc0b4ba4c8eb02a45a0ab153af5.png
[Link 2]: http://files.cnblogs.com/webabcd/Pattern.rar