PHP设计模式之观察者、原型以及装饰模式

2019/01/17PHP48502583 字6 分钟

一、观察者模式

观察者模式（ Observer ），当一个对象状态发生改变时，依赖它的对象全部会收到通知，并自动更新。
场景：一个事件发生后，要执行一连串更新操作。传统的编程方式，就是在事件的代码之后直接加入处理逻辑。当更新的逻辑增多后，代码会变得难以维护。

这种方式是耦合的，入侵式的，增加新的逻辑需要修改事件主体的代码。

观察者模式实现了低耦合，非入侵式的通知与更新机制。

实例代码：

abstract class EventGenerator{
    private $observers = array();
    public function addObsserver($observer){
    $this->observers[] = $observer;
    }
    public function notify(){
    foreach ($this->observers as $key => $observer) {
       $observer->update();
    }
    }
}
interface Observer{
    public function update($event_info = null);
}
class Event extends EventGenerator{
    public function trigger(){
    echo "事件发生";
    //update code
    $this->notify();
    }
}
class ObserverOne implements Observer{
    public function update($event_info = null){
    echo "逻辑1";
    }
}
class ObserverTwo implements Observer{
    public function update($event_info = null){
    echo "逻辑2";
    }
}
$event = new Event();
$event->addObsserver(new ObserverOne);
$event->addObsserver(new ObserverTwo);
$event->trigger();

二、原型模式

与工厂模式作用类似，都是用来创建对象。
与工厂模式的实现不懂，原型模式是首先创建好一个原型对象，然后通过clone原型对象来创建新的对象。这样就免去了类创建是重复的初始化操作。
原型模式适用于大对象的创建。创建一个大对象需要很大的开销，如果每次new就会消耗很大，原型模式仅需内存拷贝即可。

实例代码：

class Canvas{
    public $data;
    protected $decorators = array();
    public function init($width = 20, $height = 10){
        $data = array();
        for($i = 0; $i < $height; $i++){
            for($j = 0; $j < $width; $j++){
                $data[$i][$j] = '*';
            }
        }
        $this->data = $data;
    }
    public function draw(){
        foreach($this->data as $line){
            foreach($line as $char) {
                echo $char;
            }
            echo "\n";
        }
    }
    public function rect($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][$k2] = ' ';
            }
        }
    }
}
/**
 * 创建原型对象
 * [$prototype description]
 * @var Canvas
 */
$prototype = new Canvas();
$prototype->init();

$canvas = clone $prototype;//克隆原型对象
$canvas->rect(3, 6, 4, 12);
$canvas->draw();
echo "--------------";
$canvas1 = clone $prototype;
$canvas1->rect(3, 3, 3, 3);
$canvas1->draw();

三、装饰模式

1.装饰模式,可以动态的添加修改类的功能。

2.一个类提供了一项功能,如果要在修改并添加额外的功能,传统的编程模式,需要写一个之类集成它,并重新实现类的方法。

3.使用装饰模式,仅需在运行时添加一个装饰对象即可实现,可以实现最大的灵活性。

实例代码：

class Canvas{
    public $data;
    protected $decorators = array();
    public function init($width = 20, $height = 10){
        $data = array();
        for($i = 0; $i < $height; $i++){
            for($j = 0; $j < $width; $j++){
                $data[$i][$j] = '*';
            }
        }
        $this->data = $data;
    }
    public function addDecorator($decorator){
        $this->decorators[] = $decorator;
    }
    public function beforeDraw(){
        foreach($this->decorators as $decorator){
            $decorator->beforeDraw();
        }
    }
    public function afterDraw(){
        $decorators = array_reverse($this->decorators);
        foreach($decorators as $decorator){
            $decorator->afterDraw();
        }
    }
    public function draw(){
        $this->beforeDraw();
        foreach($this->data as $line){
            foreach($line as $char) {
                echo $char;
            }
            echo "\n";
        }
        $this->afterDraw();
    }
    public function rect($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] = ' ';
            }
        }
    }
}
interface DrawDecorator{
    public function beforeDraw();
    public function afterDraw();
}
class ColorDrawDecotator implements DrawDecorator{
    protected $color;
    public function __construct($color = 'red'){
    $this->color = $color;
    }
    public function beforeDraw(){
    echo "+++++++++++";
    }
    public function afterDraw(){
    echo "-----------";
    }
}
class SizeDrawDecotator implements DrawDecorator{
    protected $size;
    public function __construct($size = '12px'){
    $this->size = $size;
    }
    public function beforeDraw(){
    echo "before draw";
    }
    public function afterDraw(){
    echo "after draw";
    }
}
$canvas = new Canvas();
$canvas->init();
$canvas->addDecorator(new ColorDrawDecotator('green'));
$canvas->addDecorator(new SizeDrawDecotator('24px'));
$canvas->rect(3, 6, 4, 12);
$canvas->draw();

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PHP设计模式之观察者、原型以及装饰模式

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