CommandPattern.md

The Command Pattern

C++ Project Example

Link: Remote Control

Theory

This pattern encapsulates a request as an object, thereby letting you parameterize other objects with different requests, queue or log requests, and support undoable operations.

Class Diagram

classDiagram

class Client
class Invoker {
    setCommand()
}

class Command {
    <<interface>>
    execute()
    undo()
}

class ConcreteCommand {
    execute()
    undo()
}
class Receiver {
    action()
}

ConcreteCommand ..> Command
Invoker --> Command
Client --> Receiver
Client --> ConcreteCommand
ConcreteCommand --> Receiver

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• Command declares an interface for all commands, it has an execute() and undo() method
• The execute() method of a ConcreteCommand eventually calls the action() of Receiver
• The ConcreteCommand defines a binding between an action and a receiver
• The Client is responsible for creating a ConcreteCommand and setting its Receiver
• The Invoker holds a command and at some point asks the command to call its execute() method
• The Receiver knows how to perform the work needed to carry out the request
• The Invoker of the request and the Receiver of the request are decoupled