participants
The classes and/or objects participating in this pattern are:
- Component (LibraryItem)
- defines the interface for objects that can have responsibilities added to them dynamically.
- ConcreteComponent (Book, Video)
- defines an object to which additional responsibilities can be attached.
- Decorator (Decorator)
- maintains a reference to a Component object and defines an interface that conforms to Component's interface.
- ConcreteDecorator (Borrowable)
- adds responsibilities to the component.
有段很经典的代码：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace Decorator
{
class Program
{
static void Main(string[] args)
{
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.ReadKey();
}
/// <summary>
/// The 'Component' abstract class
/// </summary>
abstract class LibraryItem
{
private int _numCopies;
// Property
public int NumCopies
{
get { return _numCopies; }
set { _numCopies = value; }
}
public abstract void Display();
}
/// <summary>
/// The 'ConcreteComponent' class
/// </summary>
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);
}
}
/// <summary>
/// The 'ConcreteComponent' class
/// </summary>
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);
}
}
/// <summary>
/// The 'Decorator' abstract class
/// </summary>
abstract class Decorator : LibraryItem
{
protected LibraryItem libraryItem;
// Constructor
public Decorator(LibraryItem libraryItem)
{
this.libraryItem = libraryItem;
}
public override void Display()
{
libraryItem.Display();
}
}
/// <summary>
/// The 'ConcreteDecorator' class
/// </summary>
class Borrowable : Decorator
{
protected List<string> borrowers = new List<string>();
// 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);
}
}
}
}
}
现在我把Decorator 去掉了，运行结果依旧，还是很不理解Decorator 到底是做什么用途的，请高手赐教：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace Decorator
{
class Program
{
static void Main(string[] args)
{
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.ReadKey();
}
/// <summary>
/// The 'Component' abstract class
/// </summary>
abstract class LibraryItem
{
private int _numCopies;
// Property
public int NumCopies
{
get { return _numCopies; }
set { _numCopies = value; }
}
public abstract void Display();
}
/// <summary>
/// The 'ConcreteComponent' class
/// </summary>
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);
}
}
/// <summary>
/// The 'ConcreteComponent' class
/// </summary>
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);
}
}
class Borrowable : LibraryItem
{
protected List<string> borrowers = new List<string>();
public LibraryItem LibraryItem;
// Constructor
public Borrowable(LibraryItem libraryItem)
{
LibraryItem = 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()
{
LibraryItem.Display();
foreach (string borrower in borrowers)
{
Console.WriteLine(" borrower: " + borrower);
}
}
}
}
}