目的

封装调用与解耦

我们有一个调用器和一个接受器。此模式使用一个【Command】来委托接收器的方法调用，并呈现相同的方法【execute】。调用器只知道调用【execute】来处理客户机的【Command】。从而实现了接收器和调用者的解耦。

此模式的另一个方面是undo()，它取消execute()方法。命令行也可以通过聚合来组合更复杂的命令，使用最小的复制-粘贴，并依赖组合而不是继承。

例子

• 文本编辑器：所有事件都可以撤销、堆放、保存的命令。
• 大型CLI工具使用子命令来分发各种任务，并将它们打包到【模块】，每个模块都可以用命令行模式实现例如【vagrant】。

UML 图

 代码

Command.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\Command;

interface Command
{
    /**
     * this is the most important method in the Command pattern,
     * The Receiver goes in the constructor.
     */
    public function execute();
}

UndoableCommand.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\Command;

interface UndoableCommand extends Command
{
    /**
     * This method is used to undo change made by command execution
     */
    public function undo();
}

HelloCommand.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\Command;

/**
 * This concrete command calls "print" on the Receiver, but an external
 * invoker just knows that it can call "execute"
 */
class HelloCommand implements Command
{
    /**
     * Each concrete command is built with different receivers.
     * There can be one, many or completely no receivers, but there can be other commands in the parameters
     */
    public function __construct(private Receiver $output)
    {
    }

    /**
     * execute and output "Hello World".
     */
    public function execute()
    {
        // sometimes, there is no receiver and this is the command which does all the work
        $this->output->write('Hello World');
    }
}

AddMessageDateCommand.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\Command;

/**
 * This concrete command tweaks receiver to add current date to messages
 * invoker just knows that it can call "execute"
 */
class AddMessageDateCommand implements UndoableCommand
{
    /**
     * Each concrete command is built with different receivers.
     * There can be one, many or completely no receivers, but there can be other commands in the parameters.
     */
    public function __construct(private Receiver $output)
    {
    }

    /**
     * Execute and make receiver to enable displaying messages date.
     */
    public function execute()
    {
        // sometimes, there is no receiver and this is the command which
        // does all the work
        $this->output->enableDate();
    }

    /**
     * Undo the command and make receiver to disable displaying messages date.
     */
    public function undo()
    {
        // sometimes, there is no receiver and this is the command which
        // does all the work
        $this->output->disableDate();
    }
}

Receiver.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\Command;

/**
 * Receiver is a specific service with its own contract and can be only concrete.
 */
class Receiver
{
    private bool $enableDate = false;

    /**
     * @var string[]
     */
    private array $output = [];

    public function write(string $str)
    {
        if ($this->enableDate) {
            $str .= ' [' . date('Y-m-d') . ']';
        }

        $this->output[] = $str;
    }

    public function getOutput(): string
    {
        return join("\n", $this->output);
    }

    /**
     * Enable receiver to display message date
     */
    public function enableDate()
    {
        $this->enableDate = true;
    }

    /**
     * Disable receiver to display message date
     */
    public function disableDate()
    {
        $this->enableDate = false;
    }
}

Invoker.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\Command;

/**
 * Invoker is using the command given to it.
 * Example : an Application in SF2.
 */
class Invoker
{
    private Command $command;

    /**
     * in the invoker we find this kind of method for subscribing the command
     * There can be also a stack, a list, a fixed set ...
     */
    public function setCommand(Command $cmd)
    {
        $this->command = $cmd;
    }

    /**
     * executes the command; the invoker is the same whatever is the command
     */
    public function run()
    {
        $this->command->execute();
    }
}

测试

Tests/CommandTest.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\Command\Tests;

use DesignPatterns\Behavioral\Command\HelloCommand;
use DesignPatterns\Behavioral\Command\Invoker;
use DesignPatterns\Behavioral\Command\Receiver;
use PHPUnit\Framework\TestCase;

class CommandTest extends TestCase
{
    public function testInvocation()
    {
        $invoker = new Invoker();
        $receiver = new Receiver();

        $invoker->setCommand(new HelloCommand($receiver));
        $invoker->run();
        $this->assertSame('Hello World', $receiver->getOutput());
    }
}

Tests/UndoableCommandTest.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\Command\Tests;

use DesignPatterns\Behavioral\Command\AddMessageDateCommand;
use DesignPatterns\Behavioral\Command\HelloCommand;
use DesignPatterns\Behavioral\Command\Invoker;
use DesignPatterns\Behavioral\Command\Receiver;
use PHPUnit\Framework\TestCase;

class UndoableCommandTest extends TestCase
{
    public function testInvocation()
    {
        $invoker = new Invoker();
        $receiver = new Receiver();

        $invoker->setCommand(new HelloCommand($receiver));
        $invoker->run();
        $this->assertSame('Hello World', $receiver->getOutput());

        $messageDateCommand = new AddMessageDateCommand($receiver);
        $messageDateCommand->execute();

        $invoker->run();
        $this->assertSame("Hello World\nHello World [" . date('Y-m-d') . ']', $receiver->getOutput());

        $messageDateCommand->undo();

        $invoker->run();
        $this->assertSame("Hello World\nHello World [" . date('Y-m-d') . "]\nHello World", $receiver->getOutput());
    }
}