2.3. 组合模式

2.3.1. 目的

以单个对象的方式来对待一组对象

2.3.2. 例子

• form类的实例包含多个子元素，而它也像单个子元素那样响应render()请求，当调用 render() 方法时，它会历遍所有的子元素，调用 render() 方法

2.3.3. UML 图

2.3.4. 代码

你可以在 GitHub 上找到这些代码

Renderable.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Structural\Composite;

interface Renderable
{
    public function render(): string;
}

Form.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Structural\Composite;

/**
 * The composite node MUST extend the component contract. This is mandatory for building
 * a tree of components.
 */
class Form implements Renderable
{
    /**
     * @var Renderable[]
     */
    private array $elements;

    /**
     * runs through all elements and calls render() on them, then returns the complete representation
     * of the form.
     *
     * from the outside, one will not see this and the form will act like a single object instance
     */
    public function render(): string
    {
        $formCode = '<form>';

        foreach ($this->elements as $element) {
            $formCode .= $element->render();
        }

        return $formCode . '</form>';
    }

    public function addElement(Renderable $element)
    {
        $this->elements[] = $element;
    }
}

InputElement.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Structural\Composite;

class InputElement implements Renderable
{
    public function render(): string
    {
        return '<input type="text" />';
    }
}

TextElement.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Structural\Composite;

class TextElement implements Renderable
{
    public function __construct(private string $text)
    {
    }

    public function render(): string
    {
        return $this->text;
    }
}

2.3.5. 测试

Tests/CompositeTest.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Structural\Composite\Tests;

use DesignPatterns\Structural\Composite\Form;
use DesignPatterns\Structural\Composite\TextElement;
use DesignPatterns\Structural\Composite\InputElement;
use PHPUnit\Framework\TestCase;

class CompositeTest extends TestCase
{
    public function testRender()
    {
        $form = new Form();
        $form->addElement(new TextElement('Email:'));
        $form->addElement(new InputElement());
        $embed = new Form();
        $embed->addElement(new TextElement('Password:'));
        $embed->addElement(new InputElement());
        $form->addElement($embed);

        // This is just an example, in a real world scenario it is important to remember that web browsers do not
        // currently support nested forms

        $this->assertSame(
            '<form>Email:<input type="text" /><form>Password:<input type="text" /></form></form>',
            $form->render()
        );
    }
}