laravel_events&_listeners.md

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What are Laravel Events & Listeners?

• Laravel provides a simple and robust way of implementing event-driven architecture.
• Laravel's Event class provides methods for event registration, dispatching, and listening.
• Laravel's Listener interface can be implemented to handle events.

Creating an Event

• To create a new event class, use the php artisan event:generate command.
• This will create a new app/Events folder and generate a skeleton event class.
• Edit the $broadcastOn property to define the channel for broadcasting the event.
• Add any additional data that should be passed with the event to the $data property.

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Dispatching an Event

• To dispatch an event, use the event() function, passing in an instance of the event class.
• All listeners registered for the event will receive the event and can react accordingly.
• Laravel will automatically broadcast any event that has a $broadcastOn property defined.

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Creating a Listener

• To create a new listener, use the php artisan make:listener command.
• This will create a new app/Listeners folder and generate a skeleton listener class.
• Implement the handle() method to define what should happen when the event is received.
• Bind the listener to the event in the EventServiceProvider.

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Binding a Listener

• Add the listener to the $listen property on the EventServiceProvider.
• The key should be the name of the event and the value should be an array of listeners.
• If the listener is a class name, it should be specified as a string.
• If the listener is a closure, it can be specified inline.

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Variable Listener Subscriptions

• It's possible to bind a listener with variables by passing them as arguments to the listen() method.
• The variables will be passed as additional parameters to the listener's handle() method.
• This can be useful for dynamic listener subscriptions.

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Queued Listeners

• Laravel also supports queued listeners.
• To queue a listener, add the ShouldQueue interface to the listener class.
• Laravel will handle the rest for you, queuing the listener and processing it when resources are available.

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Events & Models

• Laravel offers an easy way to link events to models through event broadcasting.
• By default, Laravel will automatically broadcast events that implement the Illuminate\Broadcasting\InteractsWithSockets trait.
• This trait provides methods to define the channel and event name, and to broadcast data with the event.

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Event Discovery

• By default, Laravel will discover events within the app/Events folder and listeners within the app/Listeners folder.
• To change this, modify the $discoveredEvents and $discoveredListeners properties in EventServiceProvider.php.
• Alternatively, you can register events and listeners manually.

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Manually Registering Events & Listeners

• To register events and listeners manually, use the Event::listen() method.
• The first argument is the name of the event.
• The second argument is the listener or an array of listeners.
• You can pass a function as the second argument to define the listeners inline.

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Event Discovery & Manual Registration

• You have the option to use event discovery and manual registration together.
• In this case, Laravel will discover events automatically as well as those defined via Event::listen().
• This allows for a high degree of flexibility.

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Stopping Event Propagation

• To stop an event from propagating to other listeners, call the stopPropagation() method on the event object.
• This can be useful if a listener has taken care of an event and you want to ensure that other listeners don't take action as well.

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Prioritizing Listeners

• To define the order in which listeners should be invoked, use the priority() method.
• The lower the number, the higher the priority.
• Laravel will call the listeners in priority order.

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Subscribing to Multiple Events

• To subscribe a listener to multiple events, use the subscribe() method in the EventServiceProvider.
• The subscriber class should implement the Subscriber interface.
• All subscribed events and listeners should be defined within the subscribe() method.

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Event Firing & Testing

• When testing events, you can use Laravel's Event::fake() method to override event firing.
• After calling fake(), events will be queued but not dispatched.
• Use the Event::assertDispatched() and Event::assertNotDispatched() methods to test expected behavior.

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Event Broadcasting

• Event broadcasting is implemented using Laravel's WebSockets package.
• To broadcast an event, implement the ShouldBroadcast interface in the event class.
• Define the channel and payload that should be broadcast.

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Event Broadcasting Example

class OrderShipped implements ShouldBroadcast
{
    use InteractsWithSockets;

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

    public function broadcastOn()
    {
        return new PrivateChannel('orders.' . $this->order->user_id);
    }

    public function broadcastWith()
    {
        return ['id' => $this->order->id];
    }
}

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Laravel Events & Listeners Documentation

• Laravel Events
• Laravel Listeners
• Laravel Event Broadcasting

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References

• Laravel
• Laravel WebSockets
• Event-Driven Architecture