1. 设计模式
  2. 结构型模式
  3. 组合模式

组合模式

目的

把一组对象视为和单个对象实例拥有一样的行为。

应用场景

  • 一个表单类，用处理表单实例的方式来处理所有表单元素。当调用表单的 render() 方法时，随后它会对其所有子元素运行 render() 方法

UML 类图

组合模式类图

代码

Renderable.php

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<?php declare(strict_types = 1);

namespace DesignPatterns\Structural\Composite;

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

Form.php

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<?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();
        }

        $formCode .= '</form>';

        return $formCode;
    }

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

InputElement.php

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<?php declare(strict_types = 1);

namespace DesignPatterns\Structural\Composite;

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

TextElement.php

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<?php declare(strict_types = 1);

namespace DesignPatterns\Structural\Composite;

class TextElement implements Renderable
{
    private string $text;

    public function __construct(string $text)
    {
        $this->text = $text;
    }

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

测试

Tests/CompositeTest.php

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<?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()
        );
    }
}
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