League\Event - How to use

This is a sample script repo to illustrate how to use https://event.thephpleague.com. This repo is the answer to my question #97, on the League\Event repo.

Code is based on version 3.

This sample will simulate the creation of a new customer.

When the new customer has been set up (name, email, ...), the code will:

1. include the list of listeners for the NewCustomer event.
2. create an event's dispatcher instance
3. dispatch (run) the event

The real-world use case will be: when a new customer has been created, the program will send him/her a welcome email, subscribe him/her to our newsletter, if his/her birthday date has been introduced add an entry in the birthday calendar to send him/her mail with a discount f.i., ...

Run the script

By running php index.php on the console, you should get this:

In Avonture\Classes\Customer::__construct - A new customer has been set up.
    == SendWelcomeMessage == Congrats Albert Einstein by email (albert@emc2.uk)
    == SubscribeNewsLetter == Add Albert Einstein to our newsletter (albert@emc2.uk)
    == AddToBirthDayPlanning == Add Albert Einstein to our Happy Birthday planning

A new customer is created and the NewCustomer event is fired. There are three registered listeners (see src/Listeners/NewCustomerSubscribers.php) and each listener will be fired one after the other.

Stop propagation

See the src/Events/NewCustomer.php event. By implementing the Psr\EventDispatcher\StoppableEventInterface class, it's possible to tell to the event's dispatcher to stop propagation after having fired a given listener. This is explained in this documentation: https://www.php-fig.org/psr/psr-14/#stoppable-events.

The event should have a method called isPropagationStopped() that returns a boolean. As soon as the return if false, the dispatcher will stop even there are unprocessed listener in the pipeline.

Note: StoppableEventInterface has to be added in the Events definition, not in the Listener.

Let's try. Edit the src/Listeners/NewCustomer/SubscribeNewsLetter.php listener, and uncomment the $event->stopPropagation(); line. Run the script again (php index.php) and you'll get this:

In Avonture\Classes\Customer::__construct - A new customer has been set up.
    == SendWelcomeMessage == Congrats Albert Einstein by email (albert@emc2.uk)
    == SubscribeNewsLetter == Add Albert Einstein to our newsletter (albert@emc2.uk)

The AddToBirthDayPlanning listener wasn't called. The dispatcher has received the order to dont process next listeners.