Update event_listeners.rst

[ifeoluwafavour]

Documentation for Event Listeners component #215

[RCheesley]

Thanks so much for the great work on this PR @ifeoluwafavour - it's fantastic to see these docs coming over to the new documentation!

I've left a bunch of suggestions to fix the many Vale suggestions from Reviewdog, have a look and see what you think!

[ifeoluwafavour]

Hello @RCheesley
Thank you for your kind words. I'm learning a lot!

I have applied the suggested changes. To accurately follow the external link syntax, I created a pull request to include Symfony's docs event subscribers link file to the link folder:
https://github.com/mautic/developer-documentation-new/pull/221/checks

[RCheesley]

Some tweaks to fix the heading nestings, and I've asked the devs to do a technical review, too! Thanks for the great work so far!

[ifeoluwafavour]

Thank you @RCheesley for your guidance so far!

I changed 'Subscribers' to 'Event Sunscribers' in the recent commit. Is it a better heading name?

[RCheesley]

Looks like just a vale fix and we're good to go! 🚀 Thanks @ifeoluwafavour for all the hard work here!

[RCheesley]

Suggested change

	2) The Event class that is received by the listeners. This class should extend ``Symfony\Component\EventDispatcher\Event``. It's created when the event is dispatched and should have any information listeners need to act on it.
	2) The Event class received by the listeners. This class should extend ``Symfony\Component\EventDispatcher\Event``. It's created when dispatching the event and should have any information listeners need to act on it.

Vale recommendations

[escopecz]

A little bit more modern PHP:

Suggested change

	namespace MauticPlugin\HelloWorldBundle\EventListener;
	use Mautic\LeadBundle\Event as Events;
	use Mautic\LeadBundle\LeadEvents;
	/**
	* Class LeadSubscriber
	*
	* @package Mautic\LeadBundle\EventListener
	*/
	class LeadSubscriber extends CommonSubscriber
	{
	/**
	* @return array
	*/
	static public function getSubscribedEvents()
	{
	return array(
	LeadEvents::LEAD_POST_SAVE => array('onLeadPostSave', 0),
	LeadEvents::LEAD_POST_DELETE => array('onLeadDelete', 0)
	);
	}
	public function onLeadPostSave(LeadEvent $event)
	{
	$lead = $event->getLead();
	// do something
	}
	public function onLeadDelete(LeadEvent $event)
	{
	$lead = $event->getLead();
	$deletedId = $lead->deletedId;
	// do something
	}
	}
	// ...
	namespace MauticPlugin\HelloWorldBundle\EventListener;
	use Mautic\LeadBundle\LeadEvent;
	use Mautic\LeadBundle\LeadEvents;
	use Symfony\Component\EventDispatcher\EventSubscriberInterface;
	final class LeadSubscriber extends EventSubscriberInterface
	{
	static public function getSubscribedEvents(): array
	{
	return [
	LeadEvents::LEAD_POST_SAVE => ['onLeadPostSave', 0],
	LeadEvents::LEAD_POST_DELETE => ['onLeadDelete', 0],
	];
	}
	public function onLeadPostSave(LeadEvent $event): void
	{
	$lead = $event->getLead();
	// do something
	}
	public function onLeadDelete(LeadEvent $event): void
	{
	$lead = $event->getLead();
	$deletedId = $lead->deletedId;
	// do something
	}
	}
	// ...

[escopecz]

Suggested change

	Plugin event subscribers can extend ``\Mautic\CoreBundle\EventListener\CommonSubscriber`` which gives access to commonly used dependencies and also allows registering the subscriber service through the config file for the bundle. See :ref:`plugins/config:Service config items` for more information on registering event services.
	Plugin event subscribers can extend ``Symfony\Component\EventDispatcher\EventSubscriberInterface`` which gives access to commonly used dependencies and also allows registering the subscriber service through autowiring.

[escopecz]

Suggested change

	/**
	* Class HelloWorldEvents
	*/

The comment says the same thing as the class itself so it's not necessary

[escopecz]

Suggested change

	2) The Event class that is received by the listeners. This class should extend ``Symfony\Component\EventDispatcher\Event``. It's created when the event is dispatched and should have any information listeners need to act on it.
	2) The Event class that is received by the listeners. This class should extend ``Symfony\Contracts\EventDispatcher\Event``. It's created when the event is dispatched and should have any information listeners need to act on it.

[escopecz]

Modern PHP with types and updated Symfony namespace for Symfony 5+

Suggested change

	<?php
	// plugins\HelloWorldBundle\Event\ArmageddonEvent.php
	namespace MauticPlugin\HelloWorldBundle\Event;
	use Symfony\Component\EventDispatcher\Event;
	use MauticPlugin\HelloWorldBundle\Entity\World;
	class ArmageddonEvent extends Event
	{
	/** @var World */
	protected $world;
	/** @var bool */
	protected $falseAlarm = false;
	public function __construct(World $world)
	{
	$this->world = $world;
	}
	public function shouldPanic()
	{
	return ('earth' == $this->world->getName());
	}
	public function setIsFalseAlarm()
	{
	$this->falseAlarm = true;
	}
	public function getIsFalseAlarm()
	{
	return $this->falseAlarm;
	}
	}
	<?php
	// plugins\HelloWorldBundle\Event\ArmageddonEvent.php
	namespace MauticPlugin\HelloWorldBundle\Event;
	use Symfony\Contracts\EventDispatcher\Event;
	use MauticPlugin\HelloWorldBundle\Entity\World;
	final class ArmageddonEvent extends Event
	{
	private bool $falseAlarm = false;
	public function __construct(private World $world)
	{
	}
	public function shouldPanic(): bool
	{
	return ('earth' == $this->world->getName());
	}
	public function setIsFalseAlarm(): void
	{
	$this->falseAlarm = true;
	}
	public function getIsFalseAlarm(): bool
	{
	return $this->falseAlarm;
	}
	}