Flash messages API 

Instantiate a flash message 

Creating a flash message is achieved by instantiating an object of class \TYPO3\CMS\Core\Messaging\FlashMessage :

use TYPO3\CMS\Core\Messaging\FlashMessage;
use TYPO3\CMS\Core\Utility\GeneralUtility;
use TYPO3\CMS\Core\Type\ContextualFeedbackSeverity;

// FlashMessage($message, $title = '', $severity = ContextualFeedbackSeverity::OK, $storeInSession = false)
$message = GeneralUtility::makeInstance(FlashMessage::class,
   'My message text',
   'Message Header',
   ContextualFeedbackSeverity::WARNING,
   true
);

$message

The text of the message

$title

[optional] the header

$severity

[optional] the severity (default: ContextualFeedbackSeverity::OK)

$storeInSession

[optional] true: store in the session or false: store only in the \TYPO3\CMS\Core\Messaging\FlashMessageQueue object. Storage in the session should be used if you need the message to be still present after a redirection (default: false).

Flash messages severities 

The severity is defined by using the \TYPO3\CMS\Core\Type\ContextualFeedbackSeverity enumeration:

• ContextualFeedbackSeverity::NOTICE for notifications
• ContextualFeedbackSeverity::INFO for information messages
• ContextualFeedbackSeverity::OK for success messages
• ContextualFeedbackSeverity::WARNING for warnings
• ContextualFeedbackSeverity::ERROR for errors

Add a flash message to the queue 

In backend modules you can then make that message appear on top of the module after a page refresh or the rendering of the next page request or render it on your own where ever you want.

In this example the FlashMessageService ( \TYPO3\CMS\Core\Messaging\FlashMessageService ) is used to add a flash message at the bottom right of a module:

use TYPO3\CMS\Core\Utility\GeneralUtility;
use TYPO3\CMS\Core\Messaging\FlashMessageService;

$flashMessageService = GeneralUtility::makeInstance(FlashMessageService::class);
$messageQueue = $flashMessageService->getMessageQueueByIdentifier();
$messageQueue->addMessage($message);

The message is added to the queue and then the template class calls \TYPO3\CMS\Core\Messaging\FlashMessageQueue::renderFlashMessages() which renders all messages from the queue as inline flash messages. Here's how such a message looks like in a module:

This shows flash messages with 2 types of rendering mechanisms:

• several flash messages are displayed inline
• and an additional flash message ("Record count") is rendered as top-right notification (which automatically disappear after a short delay).

Use the FlashMessageQueue::NOTIFICATION_QUEUE to submit a flash message as top-right notifications, instead of inline:

use TYPO3\CMS\Core\Messaging\FlashMessage;
use TYPO3\CMS\Core\Messaging\FlashMessageQueue;
use TYPO3\CMS\Core\Messaging\FlashMessageService;
use TYPO3\CMS\Core\Type\ContextualFeedbackSeverity;
use TYPO3\CMS\Core\Utility\GeneralUtility;

$flashMessageService = GeneralUtility::makeInstance(FlashMessageService::class);
$notificationQueue = $flashMessageService->getMessageQueueByIdentifier(
    FlashMessageQueue::NOTIFICATION_QUEUE
);
$flashMessage = GeneralUtility::makeInstance(
    FlashMessage::class,
    'I am a message rendered as notification',
    'Hooray!',
    ContextualFeedbackSeverity::OK
);
$notificationQueue->enqueue($flashMessage);

The recommended way to show flash messages is to use the Fluid ViewHelper <f:flashMessages />. This ViewHelper works in any context because it uses the FlashMessageRendererResolver class to find the correct renderer for the current context.