目的

根据对象的状态封装一种事务的不同行为。 这更简洁的方式可以在对象在运行时更改其行为，而无需求助于大型的判断条件语句。

UML 图

代码

OrderContext.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\State;

class OrderContext
{
    private State $state;

    public static function create(): OrderContext
    {
        $order = new self();
        $order->state = new StateCreated();

        return $order;
    }

    public function setState(State $state)
    {
        $this->state = $state;
    }

    public function proceedToNext()
    {
        $this->state->proceedToNext($this);
    }

    public function toString()
    {
        return $this->state->toString();
    }
}

State.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\State;

interface State
{
    public function proceedToNext(OrderContext $context);

    public function toString(): string;
}

StateCreated.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\State;

class StateCreated implements State
{
    public function proceedToNext(OrderContext $context)
    {
        $context->setState(new StateShipped());
    }

    public function toString(): string
    {
        return 'created';
    }
}

StateShipped.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\State;

class StateShipped implements State
{
    public function proceedToNext(OrderContext $context)
    {
        $context->setState(new StateDone());
    }

    public function toString(): string
    {
        return 'shipped';
    }
}

StateDone.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\State;

class StateDone implements State
{
    public function proceedToNext(OrderContext $context)
    {
        // there is nothing more to do
    }

    public function toString(): string
    {
        return 'done';
    }
}

测试

Tests/StateTest.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\State\Tests;

use DesignPatterns\Behavioral\State\OrderContext;
use PHPUnit\Framework\TestCase;

class StateTest extends TestCase
{
    public function testIsCreatedWithStateCreated()
    {
        $orderContext = OrderContext::create();

        $this->assertSame('created', $orderContext->toString());
    }

    public function testCanProceedToStateShipped()
    {
        $contextOrder = OrderContext::create();
        $contextOrder->proceedToNext();

        $this->assertSame('shipped', $contextOrder->toString());
    }

    public function testCanProceedToStateDone()
    {
        $contextOrder = OrderContext::create();
        $contextOrder->proceedToNext();
        $contextOrder->proceedToNext();

        $this->assertSame('done', $contextOrder->toString());
    }

    public function testStateDoneIsTheLastPossibleState()
    {
        $contextOrder = OrderContext::create();
        $contextOrder->proceedToNext();
        $contextOrder->proceedToNext();
        $contextOrder->proceedToNext();

        $this->assertSame('done', $contextOrder->toString());
    }
}