Command -- Design Pattern

     Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations

Participants

  The classes and/or objects participating in this pattern are:

• Command(Command)

       Declares an interface for executing an operation

• Concrete Command(Calculator Command)

      Defines a binding between a Receiver object and an action

      Implements Execute by invoking the corresponding operation(s) on Receiver

• Client(Command App)

      Creates a Concrete Command object and sets its receiver

• Invoker(User)

       Asks the command to carry out the request

• Receiver(Calculator)

      Knows how to perform the operations associated with carrying out the request.

Example of Comand Design Pattern

using System;  namespace Command.Structural {   /// <summary>   /// MainApp startup class for Structural   /// Command Design Pattern.   /// </summary>   class MainApp   {     /// <summary>     /// Entry point into console application.     /// </summary>     static void Main()     {       // Create receiver, command, and invoker       Receiver receiver = new Receiver();       Command command = new ConcreteCommand(receiver);       Invoker invoker = new Invoker();       // Set and execute command       invoker.SetCommand(command);       invoker.ExecuteCommand();       // Wait for user       Console.ReadKey();     }   }   /// <summary>   /// The 'Command' abstract class   /// </summary>   abstract class Command   {     protected Receiver receiver;     // Constructor     public Command(Receiver receiver)     {       this.receiver = receiver;     }     public abstract void Execute();   }   /// <summary>   /// The 'ConcreteCommand' class   /// </summary>   class ConcreteCommand : Command   {     // Constructor     public ConcreteCommand(Receiver receiver) :       base(receiver)     {     }     public override void Execute()     {       receiver.Action();     }   }   /// <summary>   /// The 'Receiver' class   /// </summary>   class Receiver   {     public void Action()     {       Console.WriteLine("Called Receiver.Action()");     }   }    /// <summary>   /// The 'Invoker' class   /// </summary>   class Invoker   {     private Command _command;     public void SetCommand(Command command)     {       this._command = command;     }     public void ExecuteCommand()     {       _command.Execute();     }   } }

Output Called Receiver.Action()