Using Events

Name: SymfonyWorld Online 2021
Start: 2021-06-17
End: 2021-06-18

4.1 version

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Using Events

Using Events¶

The Application class of the Console component allows you to optionally hook into the lifecycle of a console application via events. Instead of reinventing the wheel, it uses the Symfony EventDispatcher component to do the work:

use Symfony\Component\Console\Application;
use Symfony\Component\EventDispatcher\EventDispatcher;

$dispatcher = new EventDispatcher();

$application = new Application();
$application->setDispatcher($dispatcher);
$application->run();

Caution

Console events are only triggered by the main command being executed. Commands called by the main command will not trigger any event.

The `ConsoleEvents::COMMAND` Event¶

Typical Purposes: Doing something before any command is run (like logging which command is going to be executed), or displaying something about the event to be executed.

Just before executing any command, the ConsoleEvents::COMMAND event is dispatched. Listeners receive a Symfony\Component\Console\Event\ConsoleCommandEvent event:

use Symfony\Component\Console\Event\ConsoleCommandEvent;
use Symfony\Component\Console\ConsoleEvents;

$dispatcher->addListener(ConsoleEvents::COMMAND, function (ConsoleCommandEvent $event) {
    // gets the input instance
    $input = $event->getInput();

    // gets the output instance
    $output = $event->getOutput();

    // gets the command to be executed
    $command = $event->getCommand();

    // writes something about the command
    $output->writeln(sprintf('Before running command <info>%s</info>', $command->getName()));

    // gets the application
    $application = $command->getApplication();
});

Disable Commands inside Listeners¶

Using the disableCommand() method, you can disable a command inside a listener. The application will then not execute the command, but instead will return the code 113 (defined in ConsoleCommandEvent::RETURN_CODE_DISABLED). This code is one of the reserved exit codes for console commands that conform with the C/C++ standard.:

use Symfony\Component\Console\Event\ConsoleCommandEvent;
use Symfony\Component\Console\ConsoleEvents;

$dispatcher->addListener(ConsoleEvents::COMMAND, function (ConsoleCommandEvent $event) {
    // gets the command to be executed
    $command = $event->getCommand();

    // ... check if the command can be executed

    // disables the command, this will result in the command being skipped
    // and code 113 being returned from the Application
    $event->disableCommand();

    // it is possible to enable the command in a later listener
    if (!$event->commandShouldRun()) {
        $event->enableCommand();
    }
});

The `ConsoleEvents::ERROR` Event¶

Typical Purposes: Handle exceptions thrown during the execution of a command.

Whenever an exception is thrown by a command, including those triggered from event listeners, the ConsoleEvents::ERROR event is dispatched. A listener can wrap or change the exception or do anything useful before the exception is thrown by the application.

Listeners receive a Symfony\Component\Console\Event\ConsoleErrorEvent event:

use Symfony\Component\Console\Event\ConsoleErrorEvent;
use Symfony\Component\Console\ConsoleEvents;

$dispatcher->addListener(ConsoleEvents::ERROR, function (ConsoleErrorEvent $event) {
    $output = $event->getOutput();

    $command = $event->getCommand();

    $output->writeln(sprintf('Oops, exception thrown while running command <info>%s</info>', $command->getName()));

    // gets the current exit code (the exception code or the exit code set by a ConsoleEvents::TERMINATE event)
    $exitCode = $event->getExitCode();

    // changes the exception to another one
    $event->setError(new \LogicException('Caught exception', $exitCode, $event->getError()));
});

The `ConsoleEvents::TERMINATE` Event¶

Typical Purposes: To perform some cleanup actions after the command has been executed.

After the command has been executed, the ConsoleEvents::TERMINATE event is dispatched. It can be used to do any actions that need to be executed for all commands or to cleanup what you initiated in a ConsoleEvents::COMMAND listener (like sending logs, closing a database connection, sending emails, …). A listener might also change the exit code.

Listeners receive a Symfony\Component\Console\Event\ConsoleTerminateEvent event:

use Symfony\Component\Console\Event\ConsoleTerminateEvent;
use Symfony\Component\Console\ConsoleEvents;

$dispatcher->addListener(ConsoleEvents::TERMINATE, function (ConsoleTerminateEvent $event) {
    // gets the output
    $output = $event->getOutput();

    // gets the command that has been executed
    $command = $event->getCommand();

    // displays the given content
    $output->writeln(sprintf('After running command <info>%s</info>', $command->getName()));

    // changes the exit code
    $event->setExitCode(128);
});

Tip

This event is also dispatched when an exception is thrown by the command. It is then dispatched just after the ConsoleEvents::ERROR event. The exit code received in this case is the exception code.

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