php设计模式 装饰器模式

装饰器模式，可以动态地添加修改类的功能。

一个类提供了一项功能，如果要修改并添加额外的功能，传统的编程模式需要写一个子类继承它，并重新实现类的方法。使用装饰器模式，仅需要在运行时添加一个装饰器对象即可实现，可以实现最大的灵活性。

DrawDecorator.php

<?php
namespace Baobab;
/**
 * Interface DrawDecorator
 * @package Baobab
 * 装饰器接口，定义两个方法,渲染画布之前和之后可添加额外的能力
 */
interface DrawDecorator{
    function beforeDraw();
    function afterDraw();
}

Canvas.php

<?php
namespace Baobab;

/**
*Canvas类，绘制图形
**/
class Canvas
{
    public $data;
    protected $decorators = array();

    //Decorator
    function init($width = 20, $height = 10)
    {
        $data = array();
        for($i = 0; $i < $height; $i++)
        {
            for($j = 0; $j < $width; $j++)
            {
                $data[$i][$j] = '*';
            }
        }
        $this->data = $data;
    }

    function addDecorator(DrawDecorator $decorator){
        $this->decorators[] = $decorator;
    }

    function beforeDraw(){
        foreach($this->decorators as $decorator){
            $decorator->beforeDraw();
        }
    }

    function afterDraw(){
        $decorators = array_reverse($this->decorators);
        foreach($decorators as $decorator){
            $decorator->afterDraw();
        }
    }

    function draw()
    {
        $this->beforeDraw();
        foreach($this->data as $line)
        {
            foreach($line as $char)
            {
                echo $char;
            }
            echo "<br />\n";
        }
        $this->afterDraw();
    }

    function rect($a1, $a2, $b1, $b2)
    {
        foreach($this->data as $k1 => $line)
        {
            if ($k1 < $a1 or $k1 > $a2) continue;
            foreach($line as $k2 => $char)
            {
                if ($k2 < $b1 or $k2 > $b2) continue;
                $this->data[$k1][$k2] = '&nbsp;';
            }
        }
    }
}

ColorDrawDecorator.php

<?php
namespace Baobab;
/**
*修改图形颜色的装饰器
*/
class ColorDrawDecorator implements \Baobab\DrawDecorator{
    protected $color;
    function __construct($color = 'black'){
        $this->color = $color;
    }

    function beforeDraw(){
        echo "<div style='color: {$this->color};'>";
    }
    function afterDraw(){
        echo "</div>";
    }
}

SizeDrawDecorator.php

<?php
namespace Baobab;
/**
*修改图形大小的装饰器
*/

class SizeDrawDecorator implements \Baobab\DrawDecorator{
    protected $size;
    function __construct($size = '12px'){
        $this->size = $size;
    }

    function beforeDraw()
    {
        echo "<div style='font-size: {$this->size};'>";
    }
    function afterDraw()
    {
        echo "</div>";
    }
}

index.php

$canvas = new Baobab\Canvas();
$canvas->init();
$canvas->rect(3, 6,4,12);

$canvas->addDecorator(new \Baobab\ColorDrawDecorator('blue'));
$canvas->addDecorator(new \Baobab\SizeDrawDecorator('10px'));
......
//可添加其他更多装饰器
$canvas->draw();