Dependency injection concept in PHP - Mini Project: Build & Apply

Understanding Dependency Injection in PHP

📖 Scenario: You are building a simple PHP application that sends notifications. To keep your code clean and easy to change, you want to use dependency injection. This means you will give the notification sender to the notifier instead of making the notifier create it itself.

🎯 Goal: Learn how to use dependency injection by creating a notifier class that receives a sender object. You will create the sender, inject it into the notifier, and then send a notification message.

📋 What You'll Learn

Create a class called EmailSender with a method send that prints a message.

Create a class called Notifier that accepts a sender object in its constructor and stores it.

Add a method notify in Notifier that calls the sender's send method with a message.

Create an instance of EmailSender and inject it into Notifier.

Call the notify method to send a notification.

💡 Why This Matters

🌍 Real World

Dependency injection is used in many PHP frameworks to manage how objects get their dependencies, making code easier to test and maintain.

💼 Career

Understanding dependency injection is important for working with modern PHP frameworks like Laravel or Symfony, which use this pattern extensively.

1

Create the EmailSender class

Create a class called EmailSender with a public method send that takes a parameter $message and prints "Sending email: " followed by the message.

PHP

<?php

// Create the EmailSender class with a send method
// Your code here

Need a hint?

Define a class with class EmailSender {}. Inside, add a public function send that uses echo to print the message.

2

Create the Notifier class with dependency injection

Create a class called Notifier with a private property $sender. Add a constructor that takes a parameter $sender and assigns it to the property $sender.

PHP

<?php

class EmailSender {
    public function send($message) {
        echo "Sending email: $message";
    }
}

// Create the Notifier class with a private property $sender and a constructor
// Your code here

Need a hint?

Define a class Notifier with a private property $sender. The constructor should accept $sender and assign it to $this->sender.

3

Add notify method to call sender's send

In the Notifier class, add a public method notify that takes a parameter $message and calls $this->sender->send($message).

PHP

sender = $sender;
    }

    // Add notify method that calls sender's send
    // Your code here
}

Need a hint?

Add a method notify that uses $this->sender->send($message) to send the message.

4

Create instances and send notification

Create an instance of EmailSender called $emailSender. Create an instance of Notifier called $notifier by injecting $emailSender. Call $notifier->notify("Hello World") to send the notification.

PHP

sender = $sender;
    }

    public function notify($message) {
        $this->sender->send($message);
    }
}

// Create EmailSender instance
// Create Notifier instance injecting EmailSender
// Call notify with "Hello World"
// Your code here

Need a hint?

Create the sender and inject it into the notifier. Then call notify with the message.