WordPress Notifier is an object oriented helper library for handling WordPress admin notices inside a plugin or theme. It supports persistent notices and dismissible notices out of the box and is extendable.

composer require pxlrbt/wordpress-notifier

Download and extract the library inside your project. Then include the bootstrap.php file.

require_once '[PATH_TO_FILE]/bootstrap.php';

Create a new notifier instance globally. This must be called on every page load since it automatically registers hooks for printing the admin notices. Afterwards you can create simple noticies by using notifiers static methods.

Notifier::getInstance();
#or
$notifier = new Notifier()

After creating a Notifier instance you can dispatch new notifications via it. Either use notifiers static functions for simple notifications or create a notification object yourself and configure it with it's chainable methods then dispatch it via the Notifier.

// Static functions refer to last Notifier created
Notifier::info('An update is available.');
Notifier::error('Oops, something went wrong!');

// Advanced usage
$notifier->dispatch(
    Notification::create('Plugin configuration is missing!')
        ->id('plugin_xy.config.failed')
        ->type('error')
        ->title('ERROR')
        ->dismissible(true)
        ->persistent(true);
)

Use the notification ID to check whether the notification was already dispatched.

$id = 'plugin_xy.config.failed';
$notifier->containsNotification($id);

Notifications can be dismissed manually by the user. If you need to remove persistent notification programatically set an ID and use it to remove the notification again.

$id = 'plugin_xy.config.failed';
$notifier->removeNotification($id);