1. 设计模式
  2. 行为型模式
  3. 模板方法模式

模板方法模式

目的

模板方法是一种行为设计模式。

你可能已经遇到过多次使用模板方法的场景，其核心思想是让抽象模板的子类来完成具体的算法。

这也是“好莱坞原则”：不要打电话给我们，我们会叫你。模板类不是被子类调用，而正好相反。怎么调用？当然是用抽象。

换句话说，这是一个算法骨架，很适合在框架和库代码中使用。用户只需实现指定的方法，父类就可以完成工作。

这是一种简单的解耦具体类的方法，减少了“复制/粘贴”行为，这就是为什么你会发现它随处可见。

UML 类图

模板方法模式类图

代码

Journey.php

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<?php declare(strict_types = 1);

namespace DesignPatterns\Behavioral\TemplateMethod;

abstract class Journey
{
    /**
     * @var string[]
     */
    private array $thingsToDo = [];

    /**
     * This is the public service provided by this class and its subclasses.
     * Notice it is final to "freeze" the global behavior of algorithm.
     * If you want to override this contract, make an interface with only takeATrip()
     * and subclass it.
     */
    final public function takeATrip()
    {
        $this->thingsToDo[] = $this->buyAFlight();
        $this->thingsToDo[] = $this->takePlane();
        $this->thingsToDo[] = $this->enjoyVacation();
        $buyGift = $this->buyGift();

        if ($buyGift !== null) {
            $this->thingsToDo[] = $buyGift;
        }

        $this->thingsToDo[] = $this->takePlane();
    }

    /**
     * This method must be implemented, this is the key-feature of this pattern.
     */
    abstract protected function enjoyVacation(): string;

    /**
     * This method is also part of the algorithm but it is optional.
     * You can override it only if you need to
     */
    protected function buyGift(): ?string
    {
        return null;
    }

    private function buyAFlight(): string
    {
        return 'Buy a flight ticket';
    }

    private function takePlane(): string
    {
        return 'Taking the plane';
    }

    /**
     * @return string[]
     */
    public function getThingsToDo(): array
    {
        return $this->thingsToDo;
    }
}

BeachJourney.php

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<?php declare(strict_types = 1);

namespace DesignPatterns\Behavioral\TemplateMethod;

class BeachJourney extends Journey
{
    protected function enjoyVacation(): string
    {
        return "Swimming and sun-bathing";
    }
}

CityJourney.php

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<?php declare(strict_types = 1);

namespace DesignPatterns\Behavioral\TemplateMethod;

class CityJourney extends Journey
{
    protected function enjoyVacation(): string
    {
        return "Eat, drink, take photos and sleep";
    }

    protected function buyGift(): ?string
    {
        return "Buy a gift";
    }
}

测试

Tests/JourneyTest.php

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<?php declare(strict_types = 1);

namespace DesignPatterns\Behavioral\TemplateMethod\Tests;

use DesignPatterns\Behavioral\TemplateMethod\BeachJourney;
use DesignPatterns\Behavioral\TemplateMethod\CityJourney;
use PHPUnit\Framework\TestCase;

class JourneyTest extends TestCase
{
    public function testCanGetOnVacationOnTheBeach()
    {
        $beachJourney = new BeachJourney();
        $beachJourney->takeATrip();

        $this->assertSame(
            ['Buy a flight ticket', 'Taking the plane', 'Swimming and sun-bathing', 'Taking the plane'],
            $beachJourney->getThingsToDo()
        );
    }

    public function testCanGetOnAJourneyToACity()
    {
        $cityJourney = new CityJourney();
        $cityJourney->takeATrip();

        $this->assertSame(
            [
                'Buy a flight ticket',
                'Taking the plane',
                'Eat, drink, take photos and sleep',
                'Buy a gift',
                'Taking the plane'
            ],
            $cityJourney->getThingsToDo()
        );
    }
}
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