Observer pattern in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare the Observer interface.

PHP

<?php
interface [1] {
    public function update();
}
?>

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AObservable

BListener

CSubject

DObserver

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Subject' instead of 'Observer' as interface name.

Naming the interface 'Listener' which is not standard here.

The Observer pattern requires an Observer interface that defines the update() method.

2fill in blank

medium

Complete the code to add an observer to the subject.

PHP

<?php
class Subject {
    private $observers = [];

    public function [1](Observer $observer) {
        $this->observers[] = $observer;
    }
}
?>

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Aattach

BaddObserver

CregisterObserver

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'addObserver' which is common in other languages but not here.

Using 'add' which is too generic.

The method to add an observer is commonly named attach in PHP Observer implementations.

3fill in blank

hard

Fix the error in the notifyObservers method to call update on each observer.

PHP

<?php
class Subject {
    private $observers = [];

    public function notifyObservers() {
        foreach ($this->observers as $observer) {
            $observer->[1]();
        }
    }
}
?>

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Anotify

Bupdate

Crefresh

Dcall

Attempts:

3 left

💡 Hint

Common Mistakes

Calling a non-existent method like 'notify' or 'refresh'.

Using 'call' which is not a method name.

The update() method is the standard method called on observers to notify them of changes.

4fill in blank

hard

Fill both blanks to complete the observer class that implements the Observer interface.

PHP

<?php
class ConcreteObserver implements [1] {
    public function [2]() {
        echo "Observer notified!";
    }
}
?>

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AObserver

BSubject

Cupdate

Dnotify

Attempts:

3 left

💡 Hint

Common Mistakes

Implementing 'Subject' instead of 'Observer'.

Naming the method 'notify' instead of 'update'.

The class must implement the Observer interface and define the update() method.

5fill in blank

hard

Fill all three blanks to complete the Subject class with attach, detach, and notify methods.

PHP

<?php
class Subject {
    private $observers = [];

    public function [1](Observer $observer) {
        $this->observers[] = $observer;
    }

    public function [2](Observer $observer) {
        $index = array_search($observer, $this->observers, true);
        if ($index !== false) {
            unset($this->observers[$index]);
        }
    }

    public function [3]() {
        foreach ($this->observers as $observer) {
            $observer->update();
        }
    }
}
?>

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Aattach

Bdetach

CnotifyObservers

DremoveObserver

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'addObserver' or 'removeObserver' instead of 'attach' and 'detach'.

Naming notify method simply 'notify' instead of 'notifyObservers'.

The Subject class uses attach to add, detach to remove, and notifyObservers to notify all observers.