Observer Design Pattern

Observer/example_one.php

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+<?php
+####################################
+##### OBSERVER DESIGN PATTERN #####
+####################################
+class Model implements SplSubject
+{
+ protected $observers;
+
+ /**
+ * Store observers in SplObjectStorage
+ */
+ public function __construct()
+ {
+ $this->observers = new SplObjectStorage();
+ }
+
+ /**
+ * Attach observer
+ * @param SplObserver $observer
+ * @return void
+ */
+ public function attach(SplObserver $observer)
+ {
+ $this->observers->attach($observer);
+ }
+
+ /**
+ * Detach observer
+ * @param SplObserver $observer
+ * @return void
+ */
+ public function detach(SplObserver $observer)
+ {
+ $this->observers->detach($observer);
+ }
+
+ /**
+ * When model subject is updated notify the observer
+ * @return void
+ */
+ public function notify()
+ {
+ foreach ($this->observers as $observer) {
+ $observer->update($this);
+ }
+ }
+
+ /**
+ * This method set any anonymous property
+ * @param $name
+ * @param $value
+ * @return void
+ */
+ public function __set($name, $value)
+ {
+ $this->data[$name] = $value;
+ $this->notify();
+ }
+}
+
+
+class ModelObserver implements SplObserver
+{
+ /**
+ * Notify when subject is updated
+ * @param SplSubject $subject
+ * @return void
+ */
+ public function update(SplSubject $subject)
+ {
+ echo get_class($subject) . ' has been updated' . '<br>';
+ }
+}
+
+class Observer2 implements SplObserver
+{
+ /**
+ * Notify when subject is udpated
+ * @param SplSubject $subject
+ * @return void
+ */
+ public function update(SplSubject $subject)
+ {
+ echo get_class($subject) . ' has been updated' . '<br>';
+ }
+}
+
+
+// Instantiate the model class for 2 different objects
+$model1 = new Model();
+$model2 = new Model();
+
+// Instantiate the observers
+$modelObserver = new ModelObserver();
+$observer2 = new Observer2();
+
+// Attach the observers to $model1
+$model1->attach($modelObserver);
+$model2->attach($observer2);
+
+// Attach the observers to $model2
+$model2->attach($observer2);
+
+// Change the subject properties
+$model1->title = 'Ba Ba Black Ship..';
+$model2->body = 'Twinkle Twinkle Little Star..';

Observer/example_two.php

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+<?php
+####################################
+##### OBSERVER DESIGN PATTERN #####
+####################################
+abstract class AbstractSubject
+{
+ /**
+ * Attach observer
+ * @param AbstractObserver $observer_in
+ * @return mixed
+ */
+ abstract function attach(AbstractObserver $observer_in);
+
+ /**
+ * Detach observer
+ * @param AbstractObserver $observer_in
+ * @return mixed
+ */
+ abstract function detach(AbstractObserver $observer_in);
+
+ /**
+ * Notify observer
+ * @return mixed
+ */
+ abstract function notify();
+}
+
+abstract class AbstractObserver
+{
+ /**
+ * Subject updated
+ * @param AbstractSubject $subject_in
+ * @return mixed
+ */
+ abstract function update(AbstractSubject $subject_in);
+}
+
+class Subject extends AbstractSubject
+{
+
+ private $observers = array();
+
+ function __construct(){}
+
+ /**
+ * Attach observer
+ * @param AbstractObserver $observer_in
+ * @return mixed|void
+ */
+ function attach(AbstractObserver $observer_in)
+ {
+ //could also use array_push($this->observers, $observer_in);
+ $this->observers[] = $observer_in;
+ }
+
+ /**
+ * Detach observer
+ * @param AbstractObserver $observer_in
+ * @return mixed|void
+ */
+ function detach(AbstractObserver $observer_in)
+ {
+ //$key = array_search($observer_in, $this->observers);
+ foreach ($this->observers as $okey => $oval) {
+ if ($oval == $observer_in) {
+ unset($this->observers[$okey]);
+ }
+ }
+ }
+
+ /**
+ * Notify observer
+ * @return mixed|void
+ */
+ function notify()
+ {
+ foreach ($this->observers as $obs) {
+ $obs->update($this);
+ }
+ }
+
+ /**
+ * Update subject property and notify observer
+ * @param $newFavorites
+ * @return void
+ */
+ function updateFavorites($newFavorites)
+ {
+ $this->favorites = $newFavorites;
+ $this->notify();
+ }
+
+ /**
+ * Get updated info
+ * @return mixed
+ */
+ function getFavorites()
+ {
+ return $this->favorites;
+ }
+
+}
+
+class Observer extends AbstractObserver
+{
+ /**
+ * Notify when subject is updated
+ * @param AbstractSubject $subject
+ * @return mixed|void
+ */
+ public function update(AbstractSubject $subject)
+ {
+ echo get_class($subject) . ' has been updated' . '<br>';
+ }
+}
+
+// Instantiate the subject
+$subject = new Subject();
+
+// Instantiate the observers
+$observer = new Observer();
+
+// Attach the observers to subject
+$subject->attach($observer);
+$subject->updateFavorites('Hello Subject Updated');
+$subject->updateFavorites('Hello Subject Again Updated');
+
+// Detach the observer
+$subject->detach($observer);
+
+?>