Dependency Injection

Dependency injection is a programming technique that makes a class independent of its dependencies. It achieves that by decoupling the usage of an object from its creation.


Example
Setup/Dependency:

• composer require symfony/dependency-injection
• composer require symfony/yaml
• composer require symfony/config
• Create folder "src"
• Add entry in composer.json "autoload":{"psr-4"{"DI\\": "src/"}
• and then run composer dump-autoload -o

File: /Src/Mail.php
<?php
namespace DI;
class Mail{
    private $cc;
    function __construct($fromname,$fromemail)
    {
        $this->fromname = $fromname;
        $this->fromemail = $fromemail;
    }
    function sendMail($to,$subject,$message)
    {
         $headers = "MIME-Version: 1.0" . "\r\n";
         $headers .= "Content-type:text/html;charset=UTF-8" . "\r\n";
         // More headers
         $headers .= 'From: '.$this->fromemail.'<'.$this->fromemail.'>' . "\r\n";
         mail($to,$subject,$message,$headers);
    }
}


File: /src/Notification.php

<?php
namespace DI;


class Notification{
    function __construct(Mail $mail)
    {
        $mail->sendMail("shanky@tech.com","Test Class","Welcome to Dependency Injection course.");
    }

 }


File: /index.php
<?php
require_once('vendor/autoload.php');
use DI\Mail;
use Symfony\Component\DependencyInjection\ContainerBuilder;
use Symfony\Component\DependencyInjection\Reference;
use Symfony\Component\Config\FileLocator;
use Symfony\Component\DependencyInjection\Loader\YamlFileLoader;

$container->setParameter('mailer.from_name', 'sendmail');
$container->setParameter('mailer.from_email', 'sendmail');
$container->register('mail', 'DI\Mail')->addArgument('%mailer.from_name%','%mailer.from_email%');;
$container->register('notification', 'DI\Notification')->addArgument(new Reference('mail'));