The SplSubject interface

    (PHP 5 >= 5.1.0, PHP 7, PHP 8)

    Einführung

    The SplSubject interface is used alongside SplObserver to implement the Observer Design Pattern.

    Interface-Übersicht

    interface SplSubject {
    /* Methoden */
    public attach(SplObserver $observer): void
    public detach(SplObserver $observer): void
    public notify(): void
    }

    Inhaltsverzeichnis

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    User Contributed Notes 4 notes

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    23
    przemyslaw dot szpiler at gmail dot com
    12 years ago
    <?php

    // Example implementation of Observer design pattern:

    class MyObserver1 implements SplObserver {
    public function     update(SplSubject $subject) {
    echo     __CLASS__ . ' - ' . $subject->getName();
    }
    }

    class     MyObserver2 implements SplObserver {
    public function     update(SplSubject $subject) {
    echo     __CLASS__ . ' - ' . $subject->getName();
    }
    }

    class     MySubject implements SplSubject {
    private     $_observers;
    private     $_name;

    public function     __construct($name) {
    $this->_observers = new SplObjectStorage();
    $this->_name = $name;
    }

    public function     attach(SplObserver $observer) {
    $this->_observers->attach($observer);
    }

    public function     detach(SplObserver $observer) {
    $this->_observers->detach($observer);
    }

    public function     notify() {
    foreach (    $this->_observers as $observer) {
    $observer->update($this);
    }
    }

    public function     getName() {
    return     $this->_name;
    }
    }

    $observer1 = new MyObserver1();
    $observer2 = new MyObserver2();

    $subject = new MySubject("test");

    $subject->attach($observer1);
    $subject->attach($observer2);
    $subject->notify();

    /*
    will output:

    MyObserver1 - test
    MyObserver2 - test
    */

    $subject->detach($observer2);
    $subject->notify();

    /*
    will output:

    MyObserver1 - test
    */

    ?>
    up
    2
    xedin dot unknown at gmail dot com
    5 years ago
    For a few years, I've made a few attempts to understand the architecture behind the Subject/Observer pair. Recently I tried again. I just could not imagine why someone would design this in the way it is documented. I mean, "what were they thinking?!", I thought. The if things outside of the Subject could tell it when to notify observers, that would completely break encapsulation. Because only the subject can know when events occur inside of it. And therefore, exposing `notify()` would be a huge violation to many principles of good OOP design.

    However, I have come up with one scenario where this would be valid. That is, if the Subject represents a Hook, like in WordPress. For example, in an event system where events are invoked with a name or code, a Hook could represent a named event in the system, and by calling `notify()` from outside the dispatcher could notify observers. If this is the intended scenario, then the problems are mostly with naming: the name "Subject" implies that it is what is being observed, and the Observer pattern is different.
    up
    3
    Anonymous
    11 years ago
    <?php
    class Observable implements SplSubject
    {
    private     $storage;

    function     __construct()
    {
    $this->storage = new SplObjectStorage();
    }

    function     attach(SplObserver $observer)
    {
    $this->storage->attach($observer);
    }

    function     detach(SplObserver $observer)
    {
    $this->storage->detach($observer);
    }

    function     notify()
    {
    foreach (    $this->storage as $obj) {
    $obj->update($this);
    }
    }
    //...
    }

    abstract class     Observer implements SplObserver
    {
    private     $observable;

    function     __construct(Observable $observable)
    {
    $this->observable = $observable;
    $observable->attach($this);
    }

    function     update(SplSubject $subject)
    {
    if (    $subject === $this->observable) {
    $this->doUpdate($subject);
    }
    }

    abstract function     doUpdate(Observable $observable);
    }

    class     ConcreteObserver extends Observer
    {
    function     doUpdate(Observable $observable)
    {
    //...
    }
    }

    $observable = new Observable();
    new     ConcreteObserver($observable);
    up
    2
    aiddroid at example dot com
    11 years ago
    /**
    * Subject,that who makes news
    */
    class Newspaper implements \SplSubject{
    private $name;
    private $observers = array();
    private $content;

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

    //add observer
    public function attach(\SplObserver $observer) {
    $this->observers[] = $observer;
    }

    //remove observer
    public function detach(\SplObserver $observer) {

    $key = array_search($observer,$this->observers, true);
    if($key){
    unset($this->observers[$key]);
    }
    }

    //set breakouts news
    public function breakOutNews($content) {
    $this->content = $content;
    $this->notify();
    }

    public function getContent() {
    return $this->content." (by {$this->name})";
    }

    //notify observers(or some of them)
    public function notify() {
    foreach ($this->observers as $value) {
    $value->update($this);
    }
    }
    }

    /**
    * Observer,that who recieves news
    */
    class Reader implements SplObserver{
    private $name;

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

    public function update(\SplSubject $subject) {
    echo $this->name.' is reading breakout news <b>'.$subject->getContent().'</b><br>';
    }
    }

    //classes test
    $newspaper = new Newspaper('Newyork Times');

    $allen = new Reader('Allen');
    $jim = new Reader('Jim');
    $linda = new Reader('Linda');

    //add reader
    $newspaper->attach($allen);
    $newspaper->attach($jim);
    $newspaper->attach($linda);

    //remove reader
    $newspaper->detach($linda);

    //set break outs
    $newspaper->breakOutNews('USA break down!');

    //=========output==========
    //Allen is reading breakout news USA break down! (by Newyork Times)
    //Jim is reading breakout news USA break down! (by Newyork Times)
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