The SplObserver interface

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

    Introduction

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

    Interface synopsis

    interface SplObserver {
    /* Methods */
    public update(SplSubject $subject): void
    }

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    User Contributed Notes 2 notes

    up
    107
    aiddroid at example dot com
    11 years ago
    <?php

    /**
    * 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     $this->content." ({$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>';
    }
    }

    $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! (Newyork Times)
    //Jim is reading breakout news USA break down! (Newyork Times)
    up
    98
    sebastien dot ferrandez at free dot fr
    10 years ago
    Beware, you have written :

    if($key){
    unset($this->observers[$key]);
    }

    When this should be :

    if(false !== $key){
    unset($this->observers[$key]);
    }

    If the observer you want to delete is the first in your array, you will never delete it because the key would equal 0 and 0 == false as you know.
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