Symfony Kernel Events Default Method Name

Symfony-Event-Dispatcher.md

How does Symfony determine the name of the method to call in an event listener on a kernel event?

In regard to this question, the official Symfony documentation states:

Symfony follows this logic to decide which method to execute inside the event listener class:

1. If the kernel.event_listener tag defines the method attribute, that's the name of the method to be executed;

2. If no method attribute is defined, try to execute the method whose name is on + "camel-cased event name" (e.g. onKernelException() method for the kernel.exception event);

3. If that method is not defined either, try to execute the __invoke() magic method (which makes event listeners invokable);

4. If the _invoke() method is not defined either, throw an exception.

There is an optional attribute for the kernel.event_listener tag called priority, which is a positive or negative integer that defaults to 0 and it controls the order in which listeners are executed (the higher the number, the earlier a listener is executed). This is useful when you need to guarantee that one listener is executed before another. The priorities of the internal Symfony listeners usually range from -256 to 256 but your own listeners can use any positive or negative integer.

https://github.com/symfony/event-dispatcher/blob/master/DependencyInjection/RegisterListenersPass.php#L100