Command

Context: Encapsulate a request as an object, thereby letting you parameterize clients with queues, requests, and operations.

public interface ICommand
{
    void Execute();
}

public class Receiver
{
    public void Action() => Console.WriteLine("Receiver action");
}

public class ConcreteCommand : ICommand
{
    private Receiver _receiver;
    public ConcreteCommand(Receiver receiver) => _receiver = receiver;
    public void Execute() => _receiver.Action();
}

public class Invoker
{
    private ICommand _command;
    public void SetCommand(ICommand command) => _command = command;
    public void PressButton() => _command.Execute();
}

Real-world usage example

Undo/redo in editors: Each user action (insert, delete, format) becomes a command with Execute() and Undo(). The history stack stores commands for undo/redo.

Example: In ASP.NET Core MVC, controller actions are command objects. Also, ICommand in WPF/MVVM and BackgroundService with command queuing.

Related sections

• 5.3 Behavioural patterns
• 5.3.1 Strategy
• 5.3.3 Observer