In this article, we are going to explore the basics of event management in Laravel. It’s one of the important features that you, as a developer, should have in your arsenal in your desired framework. As we move on, we’ll also grab this opportunity to create a real-world example of a custom event and listener, and that’s the ultimate goal of this article as well.
The concept of events in Laravel is based on a very popular software design pattern—the observer pattern. In this pattern, the system is supposed to raise events when something happens, and you could define listeners that listen to these events and react accordingly. It’s a really useful feature in a way that allows you to decouple components in a system that otherwise would have resulted in tightly coupled code.
For example, say you want to notify all modules in a system when someone logs into your site. Thus, it allows them to react to this login event, whether it’s about sending an email or in-app notification or for that matter anything that wants to react to this login event.
Basics of Events and Listeners
In this section, we’ll explore Laravel’s way of implementing events and listeners in the core framework. If you’re familiar with the architecture of Laravel, you probably know that Laravel implements the concept of a service provider that allows you to inject different services into an application.
Similarly, Laravel provides a built-in EventServiceProvider.php
class that allows us to define event listener mappings for an application.
Go ahead and pull in the app/Providers/EventServiceProvider.php
file.
[ 'AppListenersEventListener', ], ]; /** * Register any events for your application. * * @return void */ public function boot() { parent::boot(); // } }
Let’s have a close look at the $listen
property, which allows you to define an array of events and associated listeners. The array keys correspond to events in a system, and their values correspond to listeners that will be triggered when the corresponding event is raised in a system.
I prefer to go through a real-world example to demonstrate it further. As you probably know, Laravel provides a built-in authentication system that facilitates features like login, register, and the like.
Assume that you want to send the email notification, as a security measure, when someone logs into the application. If Laravel didn’t support the event listener feature, you might have ended up editing the core class or some other way to plug in your code that sends an email.
In fact, you’re on the luckier side as Laravel helps you to solve this problem using the event listener. Let’s revise the app/Providers/EventServiceProvider.php
file to look like the following.
[ 'AppListenersSendEmailNotification', ], ]; /** * Register any events for your application. * * @return void */ public function boot() { parent::boot(); // } }
IlluminateAuthEventsLogin
is an event that’ll be raised by the Auth
plugin when someone logs into an application. We’ve bound that event to the AppListenersSendEmailNotification
listener, so it’ll be triggered on the login event.
Of course, you need to define the AppListenersSendEmailNotification
listener class in the first place. As always, Laravel allows you to create a template code of a listener using the artisan command.
php artisan event:generate
This command generates event and listener classes listed under the $listen
property.
In our case, the IlluminateAuthEventsLogin
event already exists, so it only creates the AppListenersSendEmailNotification
listener class. In fact, it would have created the IlluminateAuthEventsLogin
event class too if it didn’t exist in the first place.
Let’s have a look at the listener class created at app/Listeners/SendEmailNotification.php
.
It's the
handle
method that will be invoked with appropriate dependencies whenever the listener is triggered. In our case, the$event
argument should contain contextual information about the login event—logged in user information.And we can use the
$event
object to carry out further processing in thehandle
method. In our case, we want to send the email notification to the logged in user.The revised
handle
method may look something like:public function handle(Login $event) { // get logged in user's email and username $email = $event->user->email; $username = $event->user->name; // send email notification about login }So that's how you're supposed to use the events feature in Laravel. From the next section onwards, we'll go ahead and create a custom event and associated listener class.
Create a Custom Event
The example scenario that we're going to use for our example is something like this:
- An application needs to clear caches in a system at certain points. We'll raise the
CacheClear
event along with the contextual information when an application does the aforementioned. We'll pass cache group keys along with an event that was cleared. - Other modules in a system may listen to the
CacheClear
event and would like to implement code that warms up related caches.
Let's revisit the app/Providers/EventServiceProvider.php
file and register our custom event and listener mappings.
[ 'AppListenersWarmUpCache', ], ]; /** * Register any events for your application. * * @return void */ public function boot() { parent::boot(); // } }
As you can see, we've defined the AppEventsClearCache
event and associated listener class AppListenersWarmUpCache
under the $listen
property.
Next, we need to create associated class files. Recall that you could always use the artisan command to generate a base template code.
php artisan event:generate
That should have created the event class at app/Events/ClearCache.php
and the listener class at app/Listeners/WarmUpCache.php
.
With a few changes, the app/Events/ClearCache.php
class should look like this:
cache_keys = $cache_keys; } /** * Get the channels the event should broadcast on. * * @return Channel|array */ public function broadcastOn() { return new PrivateChannel('channel-name'); } }
As you've probably noticed, we've added a new property $cache_keys
that will be used to hold information that'll be passed along with an event. In our case, we'll pass cache groups that were flushed.
Next, let's have a look at the listener class with an updated handle
method at app/Listeners/WarmUpCache.php
.
cache_keys) && count($event->cache_keys)) { foreach ($event->cache_keys as $cache_key) { // generate cache for this key // warm_up_cache($cache_key) } } } }
When the listener is invoked, the handle
method is passed with the instance of the associated event. In our case, it should be the instance of the ClearCache
event that will be passed as the first argument to the handle
method.
Next, it's just a matter of iterating through each cache key and warming up associated caches.
Now, we have everything in place to test things against. Let's quickly create a controller file at app/Http/Controllers/EventController.php
to demonstrate how you could raise an event.
Firstly, we've passed an array of cache keys as the first argument while creating an instance of the
ClearCache
event.The event helper function is used to raise an event from anywhere within an application. When the event is raised, Laravel calls all listeners listening to that particular event.
In our case, the
AppListenersWarmUpCache
listener is set to listen to theAppEventsClearCache
event. Thus, thehandle
method of theAppListenersWarmUpCache
listener is invoked when the event is raised from a controller. The rest is to warm up caches that were cleared!So that's how you can create custom events in your application and work with them.
What Is an Event Subscriber?
The event subscriber allows you to subscribe multiple event listeners in a single place. Whether you want to logically group event listeners or you want to contain growing events in a single place, it's the event subscriber you're looking for.
If we had implemented the examples discussed so far in this article using the event subscriber, it might look like this.
user->email; $username = $event->user->name; // send email notification about login... } /** * Handle user logout events. */ public function warmUpCache($event) { if (isset($event->cache_keys) && count($event->cache_keys)) { foreach ($event->cache_keys as $cache_key) { // generate cache for this key // warm_up_cache($cache_key) } } } /** * Register the listeners for the subscriber. * * @param IlluminateEventsDispatcher $events */ public function subscribe($events) { $events->listen( 'IlluminateAuthEventsLogin', 'AppListenersExampleEventSubscriber@sendEmailNotification' ); $events->listen( 'AppEventsClearCache', 'AppListenersExampleEventSubscriber@warmUpCache' ); } }It's the
subscribe
method that is responsible for registering listeners. The first argument of thesubscribe
method is the instance of theIlluminateEventsDispatcher
class that you could use to bind events with listeners using thelisten
method.The first argument of the
listen
method is an event that you want to listen to, and the second argument is a listener that will be called when the event is raised.In this way, you can define multiple events and listeners in the subscriber class itself.
The event subscriber class won't be picked up automatically. You need to register it in the
EventServiceProvider.php
class under the$subscriber
property, as shown in the following snippet.So that was the event subscriber class at your disposal, and with that we've reached the end of this article as well.
Conclusion
Today we've discussed a couple of the exciting features of Laravel—events and listeners. They're based on the observer design pattern that allows you to raise application-wide events and allow other modules to listen to those events and react accordingly.
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