狀態模式，讓物件的狀態改變時，一同改變物件的行為模式，就像是大頭菜(Turnips)這個物件，有沒有壞掉只是一個狀態(State)來辨別，但如果壞掉了，那麼會因為狀態改變的關係，而讓大頭菜計算鈴錢價格的方式也跟著改變。
因為要讓大頭菜(Turnips)掛載狀態物件，所以我們要先來定義狀態，會需要提供進入到下個狀態的方法，以及 toString 來查看當前的狀態是什麼。
State.php
/**
* Interface State.
*/
interface State
{
/**
* @param Turnips $turnips
*/
public function proceedToNext(Turnips $turnips);
/**
* @return string
*/
public function toString(): string;
}首先是大頭菜剛建立出來的狀態，而大頭菜下個狀態是壞掉的狀態，所以在 proceedToNext 方法我們要將大頭菜(Turnips)來去賦予下個階段的狀態。
StateCreated.php
/**
* Class StateCreated.
*/
class StateCreated implements State
{
/**
* @param Turnips $turnips
*/
public function proceedToNext(Turnips $turnips)
{
$turnips->setState(new StateSpoiled());
}
/**
* @return string
*/
public function toString(): string
{
return 'created';
}
}再來是壞掉的大頭菜狀態，這個階段已經是最終階段了，所以在 proceedToNext 的部分則是不實作任何事。
StateSpoiled.php
/**
* Class StateSpoiled.
*/
class StateSpoiled implements State
{
/**
* @param Turnips $turnips
*/
public function proceedToNext(Turnips $turnips)
{
// there is nothing more to do
}
/**
* @return string
*/
public function toString(): string
{
return 'spoiled';
}
}最後我們要實作大頭菜(Turnips)，除了要儲存鈴錢價格(Price)、數量(Count)以外，還要儲存當前的狀態(State)，這個狀態會在一開始被建立時就擁有，並且會在執行 proceedToNext 時被變更，最後提供計算鈴錢總價格的 calculatePrice 方法，並且根據當前的狀態(State)來切換計算模式。
Turnips.php
/**
* Class Turnips.
*/
class Turnips
{
/**
* @var State
*/
protected State $state;
/**
* @var int
*/
protected int $price;
/**
* @var int
*/
protected int $count;
/**
* Turnips constructor.
*
* @param int $price
* @param int $count
*/
public function __construct(int $price, int $count)
{
$this->price = $price;
$this->count = $count;
}
/**
* @return Turnips
*/
public static function create(int $price, int $count): Turnips
{
$turnips = new self($price, $count);
$turnips->state = new StateCreated();
return $turnips;
}
/**
* @param State $state
*/
public function setState(State $state)
{
$this->state = $state;
}
/**
* @return void
*/
public function proceedToNext()
{
$this->state->proceedToNext($this);
}
/**
* @return string
*/
public function toString()
{
return $this->state->toString();
}
/**
* @return int
*/
public function calculatePrice(): int
{
switch ($this->toString()) {
case 'created':
return $this->price * $this->count;
case 'spoiled':
return 0;
}
}
}最後我們要對狀態模式做測試，測試的項目很簡單，就是建立一個大頭菜物件，這時候是健康的大頭菜，所以應該要可以得知大頭菜現在的狀態是剛建立的 created 以及正常計算鈴錢價格，再來把大頭菜切換為下個狀態，也就是壞掉的大頭菜，這時候應該要獲得壞掉的狀態 spoiled 以及計算出 0 鈴錢。
StatePatternTest.php
/**
* Class StatePatternTest.
*/
class StatePatternTest extends TestCase
{
/**
* @test
*/
public function test_state_spoiled()
{
$turnips = Turnips::create(100, 40);
$this->assertSame('created', $turnips->toString());
$this->assertEquals(4000, $turnips->calculatePrice());
$turnips->proceedToNext();
$this->assertSame('spoiled', $turnips->toString());
$this->assertEquals(0, $turnips->calculatePrice());
}
}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 ✔
==> IteratorPatternTest ✔ ✔ ✔ ✔
==> MediatorPatternTest ✔ ✔ ✔
==> MementoPatternTest ✔
==> NullObjectPatternTest ✔ ✔ ✔ ✔
==> ObserverPatternTest ✔
==> SpecificationPatternTest ✔ ✔ ✔ ✔
==> StatePatternTest ✔
==> AbstractFactoryTest ✔ ✔ ✔ ✔
==> BuilderPatternTest ✔ ✔ ✔ ✔
==> FactoryMethodTest ✔ ✔ ✔ ✔
==> PoolPatternTest ✔ ✔
==> PrototypePatternTest ✔ ✔
==> SimpleFactoryTest ✔ ✔ ✔ ✔
==> SingletonPatternTest ✔
==> StaticFactoryTest ✔ ✔ ✔ ✔ ✔
==> AdapterPatternTest ✔ ✔
==> BridgePatternTest ✔ ✔ ✔
==> CompositePatternTest ✔ ✔ ✔
==> DataMapperTest ✔ ✔
==> DecoratorPatternTest ✔ ✔
==> DependencyInjectionTest ✔ ✔ ✔
==> FacadePatternTest ✔
==> FluentInterfaceTest ✔
==> FlyweightPatternTest ✔
==> ProxyPatternTest ✔ ✔
==> RegistryPatternTest ✔ ✔ ✔ ✔ ✔
Time: 00:00.100, Memory: 8.00 MB
OK (73 tests, 145 assertions)