命令模式(Command Pattern)

  using System;
 
   class CommandPattern {
 
     // Command Pattern           Judith Bishop June 2007
     //
     // Uses a single delegate for the single type of commands that the client invokes.
 
     delegate void Invoker ();
     static Invoker Execute, Undo, Redo;
   
     class Command  {
       public Command(Receiver receiver) {  
         Execute = receiver.Action;
         Redo = receiver.Action;
         Undo = receiver.Reverse;
       }
     }
   
     public class Receiver {
       string build, oldbuild;
       string s = "some string ";
     
       public void Action() {
           oldbuild = build;
           build +=s;
           Console.WriteLine("Receiver is adding "+build);
       }
      
       public void Reverse() {
         build = oldbuild;
         Console.WriteLine("Receiver is reverting to "+build);
       }
     }
   
     static void Main() {
       new Command (new Receiver());
       Execute();
       Redo();
       Undo();
       Execute();
       Console.ReadKey();
     }
   }
  /* Output
 Receiver is adding some string 
 Receiver is adding some string some string 
 Receiver is reverting to some string 
 Receiver is adding some string some string
 */