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模式設計c#－－結構型－－decorator

名稱	Decorator
結構
意圖	動態地給一個對象添加一些額外的職責。就增加功能來說，D e c o r a t o r 模式相比生成子類更為靈活。
適用性	在不影響其他對象的情況下，以動態、透明的方式給單個對象添加職責。處理那些可以撤消的職責。當不能采用生成子類的方法進行擴充時。一種情況是，可能有大量獨立的擴展，為支持每一種組合將產生大量的子類，使得子類數目呈爆炸性增長。另一種情況可能是因為類定義被隱藏，或類定義不能用于生成子類。

Code Example

namespace?Decorator_DesignPattern

{

????using?System;

????abstract?class?Component

????{

????????public?abstract?void?Draw();?????????

????}

????class?ConcreteComponent?:?Component

????{

????????private?string?strName;

????????public?ConcreteComponent(string?s)

????????{

????????????strName?=?s;????????????

????????}

????????public?override?void?Draw()

????????{

????????????Console.WriteLine("ConcreteComponent?-?{0}",?strName);????????????

????????}????????

????}

????abstract?class?Decorator?:?Component

????{

????????protected?Component?ActualComponent;

????????public?void?SetComponent(Component?c)

????????{

????????????ActualComponent?=?c;

????????}

????????public?override?void?Draw()

????????{

????????????if?(ActualComponent?!=?null)

????????????????ActualComponent.Draw();????????

????????}

????}

????class?ConcreteDecorator?:?Decorator?

????{

????????private?string?strDecoratorName;

????????public?ConcreteDecorator?(string?str)

????????{

????????????//?how?decoration?occurs?is?localized?inside?this?decorator

????????????//?For?this?demo,?we?simply?print?a?decorator?name

????????????strDecoratorName?=?str;?

????????}

????????public?override?void?Draw()

????????{

????????????CustomDecoration();

????????????base.Draw();

????????}

????????void?CustomDecoration()

????????{

????????????Console.WriteLine("In?ConcreteDecorator:?decoration?goes?here");

????????????Console.WriteLine("{0}",?strDecoratorName);

????????}

????}

????

????///?<summary>

????///????Summary?description?for?Client.

????///?</summary>

????public?class?Client

????{

????????Component?Setup()?

????????{

????????????ConcreteComponent?c?=?new?ConcreteComponent("This?is?the?real?component");

????????????ConcreteDecorator?d?=?new?ConcreteDecorator("This?is?a?decorator?for?the?component");

????????????d.SetComponent(c);

????????????return?d;

????????}

????????

????????public?static?int?Main(string[]?args)

????????{

????????????Client?client?=?new?Client();

????????????Component?c?=?client.Setup();????

????????????//?The?code?below?will?work?equally?well?with?the?real?component,?

????????????//?or?a?decorator?for?the?component

????????????c.Draw();

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

????????????return?0;

????????}

????}

}

更好的例子區別于代理模式:
裝飾模式,對相同性質的東東的更好的一個抽象.
代理模式只是代理,所代理的對象可以有類的父子關系,但是只有一個類對象.

//?Decorator?pattern?--?Real?World?example??

using?System;

using?System.Collections;

namespace?DoFactory.GangOfFour.Decorator.RealWorld

{

??//?MainApp?test?application?

??class?MainApp

??{

????static?void?Main()

????{

??????//?Create?book?

??????Book?book?=?new?Book?("Worley",?"Inside?ASP.NET",?10);

??????book.Display();

??????//?Create?video?

??????Video?video?=?new?Video?("Spielberg",?"Jaws",?23,?92);

??????video.Display();

??????//?Make?video?borrowable,?then?borrow?and?display?

??????Console.WriteLine("\nMaking?video?borrowable:");

??????Borrowable?borrowvideo?=?new?Borrowable(video);

??????borrowvideo.BorrowItem("Customer?#1");

??????borrowvideo.BorrowItem("Customer?#2");

??????borrowvideo.Display();

??????//?Wait?for?user?

??????Console.Read();

????}

??}

??//?"Component"?

??abstract?class?LibraryItem

??{

????private?int?numCopies;

????//?Property?

????public?int?NumCopies

????{

??????get{?return?numCopies;?}

??????set{?numCopies?=?value;?}

????}

????public?abstract?void?Display();

??}

??//?"ConcreteComponent"?

??class?Book?:?LibraryItem

??{

????private?string?author;

????private?string?title;

????//?Constructor?

????public?Book(string?author,string?title,int?numCopies)

????{

??????this.author?=?author;

??????this.title?=?title;

??????this.NumCopies?=?numCopies;

????}

????public?override?void?Display()

????{

??????Console.WriteLine("\nBook?------?");

??????Console.WriteLine("?Author:?{0}",?author);

??????Console.WriteLine("?Title:?{0}",?title);

??????Console.WriteLine("?#?Copies:?{0}",?NumCopies);

????}

??}

??//?"ConcreteComponent"?

??class?Video?:?LibraryItem

??{

????private?string?director;

????private?string?title;

????private?int?playTime;

????//?Constructor?

????public?Video(string?director,?string?title,?

??????int?numCopies,?int?playTime)

????{

??????this.director?=?director;

??????this.title?=?title;

??????this.NumCopies?=?numCopies;

??????this.playTime?=?playTime;

????}

????public?override?void?Display()

????{

??????Console.WriteLine("\nVideo?-----?");

??????Console.WriteLine("?Director:?{0}",?director);

??????Console.WriteLine("?Title:?{0}",?title);

??????Console.WriteLine("?#?Copies:?{0}",?NumCopies);

??????Console.WriteLine("?Playtime:?{0}\n",?playTime);

????}

??}

??//?"Decorator"?

??abstract?class?Decorator?:?LibraryItem

??{

????protected?LibraryItem?libraryItem;

????//?Constructor?

????public?Decorator(LibraryItem?libraryItem)

????{

??????this.libraryItem?=?libraryItem;

????}

????public?override?void?Display()

????{

??????libraryItem.Display();

????}

??}

??//?"ConcreteDecorator"?

??class?Borrowable?:?Decorator

??{

????protected?ArrayList?borrowers?=?new?ArrayList();

????//?Constructor?

????public?Borrowable(LibraryItem?libraryItem)?

??????:?base(libraryItem)?

????{

????}

????public?void?BorrowItem(string?name)

????{

??????borrowers.Add(name);

??????libraryItem.NumCopies--;

????}

????public?void?ReturnItem(string?name)

????{

??????borrowers.Remove(name);

??????libraryItem.NumCopies++;

????}

????public?override?void?Display()

????{

??????base.Display();

??????

??????foreach?(string?borrower?in?borrowers)

??????{

????????Console.WriteLine("?borrower:?"?+?borrower);

??????}

????}

??}

}

Output

Book ------
Author: Worley
Title: Inside ASP.NET
# Copies: 10

Video -----
Director: Spielberg
Title: Jaws
# Copies: 23
Playtime: 92

Making video borrowable:

Video -----
Director: Spielberg
Title: Jaws
# Copies: 21
Playtime: 92

borrower: Customer #1
borrower: Customer #2

posted on 2006-01-03 15:47 夢在天涯閱讀(781) 評論(3) 編輯收藏引用所屬分類: Design pattern

裝飾模式應當在什么情況下使用
在以下情況下應當使用裝飾模式：

需要擴展一個類的功能，或給一個類增加附加責任。
需要動態地給一個對象增加功能，這些功能可以再動態地撤銷。
需要增加由一些基本功能的排列組合而產生的非常大量的功能，從而使繼承關系變得不現實。回復更多評論

# re: 模式設計c#－－結構型－－decorator 2006-04-24 15:14 夢在天涯

使用裝飾模式的優點和缺點
使用裝飾模式主要有以下的優點：

裝飾模式與繼承關系的目的都是要擴展對象的功能，但是裝飾模式可以提供比繼承更多的靈活性。
通過使用不同的具體裝飾類以及這些裝飾類的排列組合，設計師可以創造出很多不同行為的組合。
這種比繼承更加靈活機動的特性，也同時意味著裝飾模式比繼承更加易于出錯。
使用裝飾模式主要有以下的缺點：

由于使用裝飾模式，可以比使用繼承關系需要較少數目的類。使用較少的類，當然使設計比較易于進行。但是，在另一方面，使用裝飾模式會產生比使用繼承關系更多的對象。更多的對象會使得查錯變得困難，特別是這些對象看上去都很相像。

回復更多評論

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# re: 模式設計c#－－結構型－－decorator 2006-04-24 15:04 夢在天涯

# re: 模式設計c#－－結構型－－decorator 2006-04-24 15:10 夢在天涯

# re: 模式設計c#－－結構型－－decorator 2006-04-24 15:14 夢在天涯

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