How to Implement Flash Messages [Symfony]

This article explains how to implement and use flash messages in Symfony, a PHP framework.

Flash messages are a convenient feature for displaying temporary messages on the screen, such as error notifications.

Typically, they are displayed only once and then removed from the session upon page reload.

CONTROLLER DESCRIPTION

$this->addFlash('notice', 'test notice');

// or
$this->get('session')->getFlashBag()->add('notice', 'test notice');

It's that simple! This stores the flash message in the session.

The message will be displayed when you open a page configured to show flash messages.

TWIG TEMPLATE DESCRIPTION

This is for Twig, Symfony's default templating engine.

{% for message in app.flashes('notice') %}
<div>
    {{ message }}
</div>
{% endfor %}

// or
{% for message in app.session.flashBag.get('notice') %}
<div>
    {{ message }}
</div>
{% endfor %}

On the template side, since flash messages are stored as an array, you'll iterate through them using a 'for' loop or similar.

The alternative syntax below is useful to remember as it allows you to access SessionApi in addition to flashBag.

OTHER FLASH MESSAGE TOPICS

■ WHEN YOU DON'T WANT TO REMOVE A FLASH MESSAGE FROM THE SESSION AFTER DISPLAYING IT

By using `peek`, the message will not be removed from the session even after it's displayed.

{% for message in app.session.flashBag.peek('notice') %}
<div>
    {{ message }}
</div>
{% endfor %}

As an application, you can also use this when you want to retrieve a flash message on the controller side without removing it from the session.

// not clear from session
$message = $this->container->get('session')->getFlashBag()->peek('notice');

// clear from session
$message = $this->container->get('session')->getFlashBag()->get('notice');

■ CHECKING IF A FLASH MESSAGE EXISTS IN THE SESSION

Using `has` will return `true` if a flash message exists.

// Controller
$isMessage = $this->container->get('session')->getFlashBag()->has('notice');

// Template
{% if app.session.flashbag.has('notice') %}
<div>
    {{ message }}
</div>
{% endif %}

■ HOW TO RETRIEVE FROM $_SESSION

As you'll quickly see if you `dump` it, data within flash messages can also be retrieved directly from `$_SESSION['_symfony_flashes']`.

RECOMMENDED SYMFONY BOOKS

There aren't many varieties available, and since the framework itself has a vast amount of information, even introductory books offer quite a lot to read.