Facade code examples of the PHP design pattern (16)

purpose

The original purpose of the facade pattern is not to prevent you from reading complicated API documentation, it is just a side effect. In fact, its original intention is to reduce coupling and follow Demeter's law.

Facade decouples visitors and subsystems by embedding multiple (of course, sometimes only one) interfaces, while also reducing complexity.

• Facade will not prevent you from accessing the subsystem

• You can (should) provide multiple facades for a subsystem

Therefore, there will be no new in a good facade. If multiple objects are constructed in each method, then it is not a facade, but a generator or [abstract|static|simple] factory [method].

An excellent facade will not have new, and the constructor parameters are of interface type. If you need to create a new instance, pass a factory object in the parameter.

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Code

• Facade.php

<?php

namespace DesignPatterns\Structural\Facade;

class Facade
{
    /**
    * @var OsInterface
    * 定义操作系统接口变量。
    */
    private $os;

    /**
    * @var BiosInterface
    * 定义基础输入输出系统接口变量。
    */
    private $bios;

    /**
    * @param BiosInterface $bios
    * @param OsInterface $os
    * 传入基础输入输出系统接口对象 $bios 。
    * 传入操作系统接口对象 $os 。
    */
    public function __construct(BiosInterface $bios, OsInterface $os)
    {
        $this->bios = $bios;
        $this->os = $os;
    }

    /**
    * 构建基础输入输出系统执行启动方法。
    */
    public function turnOn()
    {
        $this->bios->execute();
        $this->bios->waitForKeyPress();
        $this->bios->launch($this->os);
    }

    /**
    * 构建系统关闭方法。
    */
    public function turnOff()
    {
        $this->os->halt();
        $this->bios->powerDown();
    }
}

• OsInterface.php

<?php

namespace DesignPatterns\Structural\Facade;

/**
* 创建操作系统接口类 OsInterface 。
*/
interface OsInterface
{
    /**
    * 声明关机方法。
    */
    public function halt();

    /** 
    * 声明获取名称方法，返回字符串格式数据。
    */
    public function getName(): string;
}

• BiosInterface.php

<?php

namespace DesignPatterns\Structural\Facade;

/**
* 创建基础输入输出系统接口类 BiosInterface 。
*/
interface  BiosInterface
{
    /**
    * 声明执行方法。
    */
    public function execute();

    /**
    * 声明等待密码输入方法
    */
    public function waitForKeyPress();

    /**
    * 声明登录方法。
    */
    public function launch(OsInterface $os);

    /**
    * 声明关机方法。
    */
    public function powerDown();
}

test

• Tests/FacadeTest.php

<?php

namespace DesignPatterns\Structural\Facade\Tests;

use DesignPatterns\Structural\Facade\Facade;
use DesignPatterns\Structural\Facade\OsInterface;
use PHPUnit\Framework\TestCase;

/**
* 创建自动化测试单元 FacadeTest 。
*/
class FacadeTest extends TestCase
{
    public function testComputerOn()
    {
        /** @var OsInterface|\PHPUnit_Framework_MockObject_MockObject $os */
        $os = $this->createMock('DesignPatterns\Structural\Facade\OsInterface');

        $os->method('getName')
            ->will($this->returnValue('Linux'));

        $bios = $this->getMockBuilder('DesignPatterns\Structural\Facade\BiosInterface')
            ->setMethods(['launch', 'execute', 'waitForKeyPress'])
            ->disableAutoload()
            ->getMock();

        $bios->expects($this->once())
            ->method('launch')
            ->with($os);

        $facade = new Facade($bios, $os);

        // 门面接口很简单。
        $facade->turnOn();

        // 但你也可以访问底层组件。
        $this->assertEquals('Linux', $os->getName());
    }
}

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