装饰模式(Decorator Pattern)

模式定义

装饰模式(Decorator Pattern)
动态地给一个对象增加一些额外的职责，就增加对象功能来说，装饰模式比生成子类实现更为灵活。

UML类图

• 抽象构件(Component) 需要被装饰的类，定义了对象的接口，装饰器可以给它增加额外的职责(方法)
• 具体构建(Concrete Component）实现了接口，装饰器可以给它增加额外的职责(方法)
• 抽象装饰类(Decorator） 抽象构件的子类，并有关联抽象构件类，方便调用构件方法（确保在原有方法上修改或添加职能）用于给具体构件增加职责，但是具体职责在其子类中实现

• 具体装饰类(Concrete Decorator）

  代码结果

    public static class DecoratorApp
  {
      public static void Run()
      {
          ConcreteComponent c = new ConcreteComponent();
          ConcreteDecoratorA d1 = new ConcreteDecoratorA();
          ConcreteDecoratorB d2 = new ConcreteDecoratorB();
  
          d1.SetComponent(c);
          d2.SetComponent(d1);
  
          d2.Operation();
  
          Console.ReadKey();
      }
  }
  public abstract class Componet
  {
      public abstract void Operation();
  }
  public class ConcreteComponent : Componet
  {
      public override void Operation()
      {
          Console.WriteLine("Concrete Component.Operation()");
      }
  }
  public abstract class Decorator : Componet
  {
      protected Componet component;
  
      public void SetComponent(Componet component)
      {
          this.component = component;
      }
      public override void Operation()
      {
          if (component != null)
          {
              component.Operation();
          }
      }
  }
  public class ConcreteDecoratorA : Decorator
  {
      public override void Operation()
      {
          base.Operation();
          Console.WriteLine("Concrete DecoratorA.Operation()");
      }
  }
  public class ConcreteDecoratorB : Decorator
  {
      public override void Operation()
      {
          base.Operation();
          Console.WriteLine("Concrete DecoratorB.Operation()");
          AddedBehavior();
      }
      void AddedBehavior()
      {
          Console.WriteLine("add behavior");
      }
  }

  情景模式

  这里以图书馆借阅为例，图书馆可借阅的有书和光盘，将书和光盘抽象为可借阅的东西。通过装饰类添加借阅功能。

    public static class RealWorldDecoratorApp
  {
      public static void Run()
      {
          Book book = new Book() { Author = "Worley", Title = "Inside ASP.NET", NumCopies = 10 };
          book.Display();
  
          Video video = new Video() { Director = "Spielberg", Title = "Jaws", NumCopies = 23, PlayTime = 92 };
          video.Display();
  
          Console.WriteLine("\nMaking video borrowable:");
  
          Borrowable borrowvideo = new Borrowable(video);
          borrowvideo.BorrowItem("Customer #1");
          borrowvideo.BorrowItem("Customer #2");
  
          borrowvideo.Display();
      }
  }
  public abstract class LibraryItem
  {
      public int NumCopies { get; set; }
      public abstract void Display();
  }
  public class Book : LibraryItem
  {
      public string Author { get; set; }
      public string Title { get; set; }
  
      public override void Display()
      {
          Console.WriteLine("\nBook-----");
          Console.WriteLine("Author:{0}", this.Author);
          Console.WriteLine("Title:{0}", this.Title);
          Console.WriteLine("# Copies:{0}", NumCopies);
      }
  }
  
  public class Video : LibraryItem
  {
      public string Director { get; set; }
      public string Title { get; set; }
  
      public int PlayTime { get; set; }
  
      public override void Display()
      {
          Console.WriteLine("\nVideo-----");
          Console.WriteLine("Director:{0}", this.Director);
          Console.WriteLine("Title:{0}", this.Title);
          Console.WriteLine("# Copies:{0}", NumCopies);
          Console.WriteLine("Playtime:{0}", this.PlayTime);
      }
  }
  public abstract class Decorator : LibraryItem
  {
      protected LibraryItem libraryItem;
      public Decorator(LibraryItem libraryItem)
      {
          this.libraryItem = libraryItem;
      }
      public override void Display()
      {
          libraryItem.Display();
      }
  }
  public class Borrowable : Decorator
  {
      protected List<string> borrowers = new List<string>();
      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);
          }
      }
  }