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Command Pattern

Margus Luik

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Command Pattern

Intent

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

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  • Design Patterns: Elements of Reusable Object-Oriented Software, p263

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Command Pattern

Intent of the pattern:

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

In other words:

Turn a action into data.

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Command Pattern

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Command Pattern

Characteristics

Function calls become:

  • Easy to store
  • Easy to reuse
  • Delayed if necessary
  • Configurable during runtime

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Command Pattern

Potential applications:

  • Store, queue, reuse, log and execute requests at different times.
  • Great for managing input (rebinding)
  • Decouple in game entities from players/AI
  • Support undo/redo
  • Support replays
  • Support time rewind mechanics

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Example

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Command Pattern

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Example

What parts might be:

  • Commands
  • Clients
  • Receiver
  • Invoker

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Example

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Example

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For the next week

  • Read Command chapter from Game Programming Patterns http://www.gameprogrammingpatterns.com/command.html
  • Complete tasks MoveCommand and SwitchCommand