觀察者模式的核心是將一個(gè)中心類（主體）和監(jiān)控中心類的一些觀察者做解耦合。面向?qū)ο笤O(shè)計(jì)核心思想就是面向抽象和接口編程内狸，因此具體對(duì)象間灿里，相互知道的越少越好，這樣發(fā)生改變時(shí)才不至于互相影響俯逾。因此贸桶，對(duì)于觀察者模式來說，目標(biāo)和觀察者不是緊密耦合的桌肴，目標(biāo)所知道的僅僅是它有一系列的觀察者皇筛，而觀察者屬于哪一個(gè)具體類，目標(biāo)是沒必要知道的坠七。

對(duì)于傳統(tǒng)意義上的觀察者模式來說水醋，所有的觀察者類都會(huì)實(shí)現(xiàn)一個(gè)抽象觀察者接口，中心類會(huì)保存一組觀察者對(duì)象的引用彪置，當(dāng)中心類的狀態(tài)發(fā)生改變時(shí)拄踪，調(diào)用notify方法將已保存的觀察者對(duì)象逐個(gè)更新，因?yàn)檫@是一個(gè)循環(huán)遍歷拳魁，所以要求這些觀察者對(duì)象必須有統(tǒng)一的接口惶桐。中心類同時(shí)也會(huì)有添加和移除觀察者對(duì)象的方法寓搬。（調(diào)用代碼見ClientController中的observe方法）

但在實(shí)際使用過程中泽疆，主體和觀察者可能早就已經(jīng)存在了旱爆，他們之間根本就互相不知道店乐，由客戶端來決定通知誰赶舆。如果在C#中澜驮，可以利用委托來實(shí)現(xiàn)漱逸，在php里纳决，可以用魔術(shù)方法來模擬C#里的委托释树。在主體類里增加一個(gè)$eventHandles數(shù)組肠槽，然后在客戶端將觀察者對(duì)象添加到這個(gè)數(shù)組里，這個(gè)時(shí)候相當(dāng)于主體類也神奇的擁有了這些觀察者類的方法奢啥。但這樣做對(duì)于外部世界來說署浩，提供的是一個(gè)動(dòng)態(tài)的接口，沒有辦法進(jìn)行反射扫尺，客戶程序員無法一下子理清頭緒筋栋。因此使用的時(shí)候最好有注釋或文檔提醒。（調(diào)用代碼見ClientController中的observe1方法）

<?php
namespace Basic\Logic;

class Subject
{
    private $observers = [];

    public $eventHandles = [];

    public $subjectName;

    public function __construct($subjectName)
    {
        $this->subjectName = $subjectName . ' notify --';
    }

    public function attach(Observer $observer)
    {
        array_push($this->observers, $observer);
    }

    public function detach(Observer $observer)
    {
        foreach ($this->observers as $k => $v) {
            if ($observer == $v) {
                unset($k);
                break;
            }
        }
    }

    public function notify()
    {
        /** @var Observer $observer */
        foreach ($this->observers as $observer) {
            $observer->update($this);
        }
    }

    public function notify1()
    {
        foreach ($this->eventHandles as $eventHandle) {
            if (method_exists($eventHandle['obj'], $eventHandle['func'])) {
                $eventHandle['obj']->$eventHandle['func']($this);
            }
        }
    }

    public function getState()
    {
        /** @var Observer $observer */
        foreach ($this->observers as $observer) {
            $observer->getState();
        }
    }

    public function __call($methodName, $args)
    {
        foreach ($this->eventHandles as $eventHandle) {
            if (method_exists($eventHandle, $methodName)) {
                $eventHandle->$methodName($this);
            }
        }
    }
}

<?php
namespace Basic\Logic;

abstract class Observer
{
    protected $state;

    abstract public function update(Subject $subject);

    public function getState()
    {
        echo $this->state . "<br>";
    }
}

<?php
namespace Basic\Logic;

class ObserverA extends Observer
{
    protected $state = 'ObserverA';

    public function update(Subject $subject)
    {
        $this->state = $subject->subjectName . 'notify observerA';
        echo $this->state . "<br>";
    }

    public function closeState(Subject $subject)
    {
        $this->state = $subject->subjectName . 'close observerA';
        echo $this->state . "<br>";
    }

}

<?php
namespace Basic\Logic;

class ObserverB extends Observer
{

    protected $state = 'ObserverB';

    public function update(Subject $subject)
    {
        $this->state = $subject->subjectName . 'notify observerB';
        echo $this->state . "<br>";
    }

    public function openState(Subject $subject)
    {
        $this->state = $subject->subjectName . 'open observerB';
        echo $this->state . "<br>";
    }
}

observe2方法是observe1方法的另一種更簡(jiǎn)潔的寫法正驻。這三種寫法各有利弊弊攘，具體的實(shí)現(xiàn)需要根據(jù)真實(shí)的環(huán)境來做出選擇抢腐。

<?php
namespace Basic\Controller;

use Basic\Logic\ObserverA;
use Basic\Logic\ObserverB;
use Basic\Logic\Subject;

class ClientController
{
    public function observe()
    {
        $subject = new Subject('subjectB');
        $subject->attach(new ObserverA());
        $subject->attach(new ObserverB());
        $subject->notify();
    }

    public function observe1()
    {
        $subject = new Subject('subjectB');
        $subject->eventHandles[] = new ObserverA();
        $subject->eventHandles[] = new ObserverB();
        $subject->closeState();
        $subject->openState();
    }

    public function observe2()
    {
        $subject = new Subject('subjectB');
        $subject->eventHandles[] = [
            'obj'  => new ObserverA(),
            'func' => 'closeState'
        ];
        $subject->eventHandles[] = [
            'obj'  => new ObserverB(),
            'func' => 'openState'
        ];
        $subject->notify1();
    }
}

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