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The Traceable Event Dispatcher

Name: SymfonyWorld 2021 Winter
Start: 2021-12-09
End: 2021-12-10

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The Traceable Event Dispatcher¶

The Symfony\Component\HttpKernel\Debug\TraceableEventDispatcher is an event dispatcher that wraps any other event dispatcher and can then be used to determine which event listeners have been called by the dispatcher. Pass the event dispatcher to be wrapped and an instance of the Symfony\Component\Stopwatch\Stopwatch to its constructor:

use Symfony\Component\HttpKernel\Debug\TraceableEventDispatcher;
use Symfony\Component\Stopwatch\Stopwatch;

// the event dispatcher to debug
$eventDispatcher = ...;

$traceableEventDispatcher = new TraceableEventDispatcher($eventDispatcher, new Stopwatch());

Now, the TraceableEventDispatcher can be used like any other event dispatcher to register event listeners and dispatch events:

// ...

// register an event listener
$eventListener = ...;
$priority = ...;
$traceableEventDispatcher->addListener('the-event-name', $eventListener, $priority);

// dispatch an event
$event = ...;
$traceableEventDispatcher->dispatch('the-event-name', $event);

After your application has been processed, you can use the getCalledListeners() method to retrieve an array of event listeners that have been called in your application. Similarly, the getNotCalledListeners() method returns an array of event listeners that have not been called:

// ...

$calledListeners = $traceableEventDispatcher->getCalledListeners();
$notCalledListeners = $traceableEventDispatcher->getNotCalledListeners();

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.