An easy and convenient way to create WordPress admin notices that can be closed persistently. Besides that it has some cool features:

• Keep your notices hidden only for the user who closed it.
• Display your notice on specific situations, like when some plugin gets updated or activated or on specific admin screen ids or on $_GET / $_POST requests,
• Create your own special cases where/when your notice should be displayed

add_action( 'admin_notices', function () {
	$notices_manager = \ThanksToIT\WPAN\get_notices_manager();
	$notices_manager->create_notice( array(
		'id'         => 'my-notice',
		'content'    => '<p>My Notice</p>',		
	) );
} );

Note: By default, this library will make notices persist, meaning they will not be displayed again after user close them, unless they expire

In order to make it work perfectly, you need to initialize it like this:

add_action( 'wp_ajax_' . 'tttwpan_dismiss_persist', array( 'ThanksToIT\WPAN\Notices_Manager', 'ajax_dismiss' ) );
add_action( 'activated_plugin', array( 'ThanksToIT\WPAN\Notices_Manager', 'set_activated_plugin' ) );
add_action( 'upgrader_process_complete', array( 'ThanksToIT\WPAN\Notices_Manager', 'set_upgrader_process' ), 10, 2 );

And it's important to make these calls before any other hook on your plugin/theme. But don't worry, this library will be loaded only when it's necessary, as it's being called on the proper hooks

• id (String) - Identifies the notice.
• type (String) - The type of notice, used on notice class in order to setup its color. Possible values are 'notice-info', 'notice-warning', 'notice-success', 'notice-error', 'notice-info'. Default value is 'notice-info'.
• content (String) - Notice content.
• dismissible (Boolean) - If notice should be dismissible. In other words, if you can close it. Default is true.
• dismissal_expiration (int) - How long in seconds the notice will keep closed. Values bigger than zero will make the notice persist after closed. If you set 0, it will no longer persist. Default is MONTH_IN_SECONDS.
• display_on (array) - Situations where/when the notice should be displayed. Possible values below:
  • screen_id (array). Displays the notice on specific admin screen ids. Example: 'screen_id' => array( 'plugins' ).
  • activated_plugin (array). Displays if some plugin gets activated. Example: 'activated_plugin' => array('akismet/akismet.php').
  • updated_plugin (array). Displays if some plugin gets updated. Example: 'updated_plugin' => array('akismet/akismet.php').
  • request (array) - Displays on $_GET or $_POST values. Note: It takes an array of arrays with 'key' and 'value' parameters. Example: 'request' => array( array( 'key' => 'show_notice', 'value' => '1' ), ) .
• keep_active_on (array) - Keeps the notice always opened once the display_on requirements are met, until the user close the notice. Default value is array( 'activated_plugin', 'updated_plugin' ),

add_action( 'admin_notices', function () {
	$notices_manager = \ThanksToIT\WPAN\get_notices_manager();
	$notices_manager->create_notice( array(
		'id'         => '1-week-notice',
		'content'    => '<p>1 week notice</p>',	
		'dismissal_expiration' => WEEK_IN_SECONDS,
	) );
} );

add_action( 'admin_notices', function () {
	$notices_manager = \ThanksToIT\WPAN\get_notices_manager();
	$notices_manager->create_notice( array(
		'id'         => 'plugins-page-notice',
		'content'    => '<p>plugins page notice</p>',	
		'display_on' => array(
			'screen_id' => array( 'plugins' ),			
		)
	) );
} );

add_action( 'admin_notices', function () {
	$notices_manager = \ThanksToIT\WPAN\get_notices_manager();
	$notices_manager->create_notice( array(
		'id'         => 'akismet-notice',
		'content'    => '<p>Akismet notice</p>',	
		'display_on' => array(
			'activated_plugin' => array('akismet/akismet.php')
		)
	) );
} );

To install this package, edit your composer.json file:

{
    "require": {
        "thanks-to-it/wp-admin-notices": "dev-master"
    }
}

Now run:

$ composer install