Basic Anatomy of a cron job in WordPress.php

// goes into constructor:

register_activation_hook(__FILE__, array($this, 'schedule_cache_update'));
register_deactivation_hook(__FILE__, array($this, 'clear_scheduled_event'));
add_action('proven_expert_update_cache_event', array($this, 'my_callback_function'));


// register / unregister hook on activation / deactivation of plugin
// -> proven_expert_update_cache_event wird als neue action im System registriert UND an einen cronjob gehängt!

public function schedule_cache_update() {
	if (!wp_next_scheduled('proven_expert_update_cache_event')) {
		wp_schedule_event(time(), 'hourly', 'proven_expert_update_cache_event');
	}
}

public function clear_scheduled_event() {
	$timestamp = wp_next_scheduled('proven_expert_update_cache_event');
	wp_unschedule_event($timestamp, 'proven_expert_update_cache_event');
}


// last step: implement my_callback_function that will run whenever cron job gets called

function my_callback_function() {
	echo 'ABC';
}