命令模式，是一種將行為封裝起來裹上美好糖衣的一種模式，並將接收與執行分離出來，就有點像是把大頭菜買賣這件事，如果把買大頭菜、賣大頭菜這兩個動作封裝起來，變成一個命令，分開去執行。
什麼是命令模式#
核心概念#
命令模式核心概念
命令模式將請求封裝成一個物件，使你可用不同的請求來參數化其他物件。這個模式主要將請求的發起者和接收者解耦，讓它們之間不需要直接互動。
使用時機#
適用情境
- 需要將操作參數化，可以將操作封裝成物件
- 需要在不同時間指定、排列和執行請求
- 需要支援復原(undo)操作
- 需要記錄操作日誌，以便系統重啟後恢復操作
- 需要將系統分解為高階操作構建在低階操作之上
UML#
實作#
定義命令介面（Command Interface）#
命令介面設計
首先我們要先定義命令介面(Command)，這個介面需要實作執行(execute)這個方法。這個介面定義了所有具體命令類別必須實作的方法。
Command.php#
/**
* Interface Command.
*/
interface Command
{
/**
* @return void
*/
public function execute();
}
建立命令執行者（Invoker）#
執行者設計重點
再來我們需要建立命令的執行者(Invoker)，執行者會擁有執行命令(Command)的行為，它不需要知道命令的具體內容，只需要呼叫命令的 execute 方法。
Invoker.php#
/**
* Class Invoker.
*/
class Invoker
{
/**
* @var Command
*/
protected Command $command;
/**
* @param Command $command
*/
public function setCommand(Command $command)
{
$this->command = $command;
}
/**
* @return void
*/
public function run()
{
$this->command->execute();
}
}
建立命令接收者（Receiver）#
接收者設計重點
接收者則是會有特定的功能，像是買入大頭菜、販售大頭菜。接收者知道如何實施與執行一個請求相關的操作，任何類別都可能作為一個接收者。
Receiver.php#
/**
* Class Receiver.
*/
class Receiver
{
/**
* @var int
*/
protected int $turnips = 0;
/**
* @var int
*/
protected int $bells = 0;
/**
* @param int $price
* @param int $count
*/
public function buy(int $price, int $count)
{
$total = $price * $count;
if ($this->bells < $total) {
throw new \InvalidArgumentException('您的鈴錢不足，無法購買大頭菜。');
}
$this->turnips += $count;
$this->bells -= $total;
}
/**
* @param int $price
* @param int $count
*/
public function sell(int $price, int $count)
{
if ($this->turnips < $count) {
throw new \InvalidArgumentException('您的大頭菜不足，無法販賣大頭菜。');
}
$total = $price * $count;
$this->turnips -= $count;
$this->bells += $total;
}
/**
* @param int $bells
*/
public function setBells(int $bells)
{
$this->bells += $bells;
}
/**
* @return int
*/
public function getBells(): int
{
return $this->bells;
}
}
實作具體命令（Concrete Commands）#
購買命令實作
最後要來建立購買(Buy)以及販賣(Sell)的命令(Command)，這邊會直接去執行命令所需要做的事情。購買命令會封裝購買大頭菜的操作。
BuyCommand.php#
/**
* Class BuyCommand.
*/
class BuyCommand implements Command
{
/**
* @var Receiver
*/
protected Receiver $console;
/**
* @var int
*/
protected int $price;
/**
* @var int
*/
protected int $count;
/**
* Turnips constructor.
*
* @param Receiver $console
*/
public function __construct(Receiver $console, int $price, int $count)
{
$this->console = $console;
$this->price = $price;
$this->count = $count;
}
/**
* @return void
*/
public function execute()
{
$this->console->buy($this->price, $this->count);
}
}
販賣命令實作
販賣命令會封裝販賣大頭菜的操作，同樣實作命令介面的 execute 方法。
SellCommand.php#
/**
* Class SellCommand.
*/
class SellCommand implements Command
{
/**
* @var Receiver
*/
protected Receiver $console;
/**
* @var int
*/
protected int $price;
/**
* @var int
*/
protected int $count;
/**
* Turnips constructor.
*
* @param Receiver $console
*/
public function __construct(Receiver $console, int $price, int $count)
{
$this->console = $console;
$this->price = $price;
$this->count = $count;
}
/**
* @return void
*/
public function execute()
{
$this->console->sell($this->price, $this->count);
}
}
測試#
測試目標#
測試清單
最後要對大頭菜命令模式測試一下，驗證命令模式的封裝和執行機制：
- 購買命令測試: 測試購買大頭菜的命令是否能正確執行，並正確扣除鈴錢
- 販賣命令測試: 測試販賣大頭菜的命令是否能正確執行，並正確增加鈴錢
- 命令分離測試: 驗證命令的發起者和接收者是否成功解耦
測試程式碼#
CommandPatternTest.php#
/**
* Class CommandPatternTest.
*/
class CommandPatternTest extends TestCase
{
/**
* @test
*/
public function test_invocation()
{
$invoker = new Invoker();
$receiver = new Receiver();
$receiver->setBells(10000);
$invoker->setCommand(new BuyCommand($receiver, 100, 40));
$invoker->run();
$this->assertSame(6000, $receiver->getBells());
$invoker->setCommand(new SellCommand($receiver, 200, 40));
$invoker->run();
$this->assertSame(14000, $receiver->getBells());
}
}
測試結果#
最後測試的執行結果會獲得如下：
PHPUnit Pretty Result Printer 0.28.0 by Codedungeon and contributors.
==> Configuration: ~/php-design-pattern/vendor/codedungeon/phpunit-result-printer/src/phpunit-printer.yml
PHPUnit 9.2.6 by Sebastian Bergmann and contributors.
==> ...fResponsibilitiesTest ✔ ✔ ✔
==> CommandPatternTest ✔
==> AbstractFactoryTest ✔ ✔ ✔ ✔
==> BuilderPatternTest ✔ ✔ ✔ ✔
==> FactoryMethodTest ✔ ✔ ✔ ✔
==> PoolPatternTest ✔ ✔
==> PrototypePatternTest ✔ ✔
==> SimpleFactoryTest ✔ ✔ ✔ ✔
==> SingletonPatternTest ✔
==> StaticFactoryTest ✔ ✔ ✔ ✔ ✔
==> AdapterPatternTest ✔ ✔
==> BridgePatternTest ✔ ✔ ✔
==> CompositePatternTest ✔ ✔ ✔
==> DataMapperTest ✔ ✔
==> DecoratorPatternTest ✔ ✔
==> DependencyInjectionTest ✔ ✔ ✔
==> FacadePatternTest ✔
==> FluentInterfaceTest ✔
==> FlyweightPatternTest ✔
==> ProxyPatternTest ✔ ✔
==> RegistryPatternTest ✔ ✔ ✔ ✔ ✔
Time: 00:00.062, Memory: 6.00 MB
OK (55 tests, 122 assertions)