Implementing the Observer Pattern in PHP

Welcome back! We're continuing our exploration of Behavioral Patterns. In this lesson, we will delve into the Observer Pattern, a critical design pattern that emphasizes object communication and responsibility distribution. This pattern allows an object, known as the subject, to maintain a list of its dependents, called observers, and automatically notify them of any state changes.

We previously explored the Command Pattern in PHP, which encapsulates a request as an object. Now, let's build on that knowledge and discover how the Observer Pattern facilitates seamless and efficient communication between objects.

In this lesson, you will learn how to implement the Observer Pattern by understanding its main components and roles. We'll break down the pattern into manageable parts and demonstrate its practical use with clear PHP examples.

Here's a simple illustration to get you started:

We start by defining a NewsPublisher class that maintains a list of subscribers. When new news is published, the NewsPublisher notifies all subscribers by calling their update method. Each Subscriber can then process the news as needed.

Now, let's define the Subscriber interface and a concrete implementation ConcreteSubscriber that prints the received news.

interface Subscriber {
    public function update($news);
}

class ConcreteSubscriber implements Subscriber {
    private $name;

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

    public function update($news) {
        echo "{$this->name} received news: {$news}\n";
    }
}