Registering and using actions which return results in a Plugin class

Question

I have a plugin class which contains a function spektrix_list_events()

class SpektrixPlugin {

    public function __construct(){

        add_action( 'init', array ( $this, 'init' ));
    }

    public function init()
    {
        add_action( 'spektrix_list_events', array ( $this, 'spektrix_list_events' ));
    }

    public function spektrix_list_events($getPrices = FALSE) {
        $api = new SpektrixApiClient();
        return $api->getAllEvents($getPrices);

    }
}

$SpektrixEvents = new SpektrixPlugin;
add_action('init', array($SpektrixEvents, 'init'));

In a template file, I want to be able to call do_action('spektrix_list_events') but can't seem to get this working. I've tried following the advice here

Additional question - is using add_action() the recommended way to do this?

UPDATE:

The method is in fact being called but no results are returned. So how should one call a plugin class method which returns some output for display?

Answer 1

Some actions hooks need to be fired on specific events. Try this code:

class SpektrixPlugin {

    public function __construct(){
        add_action('init', array(&$this, 'init'));
    }

    public function spektrix_list_events($getPrices = FALSE) {
        $api = new SpektrixApiClient();
        return $api->getAllEvents($getPrices);
    }

    public function init(){
        add_action( 'spektrix_list_events', array ( $this, 'spektrix_list_events' ));
    }

 }

 $SpektrixEvents = new SpektrixPlugin();

I've tested this code and it works:

class SpektrixPlugin {

    public function __construct(){
        add_action('init', array(&$this, 'init'));
    }

    public function spektrix_list_events() {
        echo 'test';
    }

    public function init(){
        add_action( 'spektrix_list_events', array ( $this, 'spektrix_list_events' ));
    }

 }

 $SpektrixEvents = new SpektrixPlugin();

 //this print 'test', so it works.
 do_action('spektrix_list_events');

But .... I've been reading the Wordpress documentation about do_action() and it says clearly that do_action() will call the function/method but it won't return anything. Quoteing Wordpress about do_action():

This function works similar to apply_filters() with the exception that nothing is returned and only the functions or methods are called.

So, you should check the apply_filters() function which works in a similar way that do_action() but can return the value returned by the called method or look for another implementation. do_action() is not suitable to return values.

An example usgin apply_filters:

class SpektrixPlugin {

    public function __construct(){
        add_action('init', array(&$this, 'init'));
    }

    public function spektrix_list_events() {
        $myvar = "Hey, I'm works";
        return $myvar;
    }

    public function init(){
        add_filter( 'spektrix_list_events', array ( $this, 'spektrix_list_events' ));
    }

 }

 $SpektrixEvents = new SpektrixPlugin;

 $test = apply_filters('spektrix_list_events','');
 var_dump($test);

Anyway, I think that this approach used to get data is no the appropiate. Although apply_filters() will work to get a value, as in the above example, the function is specially designed to filter a value, not to get one. I think the best you can do is have a get method in your class used to get the value you want, then you can apply filters to that value or do actions with it.

Answer 2

When working with classes and action, is a good practise, give an easy way to remove the action.

Using something like add_action( 'init', array ( $this, 'init' )); removing this action, can be done, but is far from easy.

Another thing to consider, is that if you plain to use a plugin from theme, is a good idea insert some custom filters and actions hooks to customize the behavior of your plugin form themes.

So, in your case you can do something like this

add_action('init', 'initSpektrixPlugin');

function initSpektrixPlugin() {
  // if the class isn't in the main plugin file, you can require class file here, e.g.:
  // require_once( plugin_dir_path(__FILE__) . 'inc/SpektrixPlugin.class.php' );
  SpektrixPlugin::init();
}

After that, the class can be something like this:

class SpektrixPlugin {

    protected static $events = array();

    public static function init()
    {
        add_action( 'spektrix_list_events', array ( __CLASS__, 'printEvents' ) );
    }

    protected static function getEvents( $getPrices = false )
    {
        $cached = self::getCachedEvents( $getPrices );
        if ( $cached ) 
           // last 'true' param means we are returning cached result
           return apply_filters('spektrix_events', $cached, $getPrices, true);
        // requiring the api client class from here, you include it
        // only if you don't already have cached results
        require_once( plugin_dir_path(__FILE__) . 'SpektrixApiClient.php' );
        $api = new SpektrixApiClient();
        $events = self::setCachedEvents( $api->getAllEvents($getPrices), $getPrices);
        // a custom action to customize behavior from theme
        do_action('spektrix_events_getted', $events, $getPrices);
        // return events after a custom filter, to customize behavior from theme
        // last 'false' param means we are returning not cached result
        return apply_filters('spektrix_events', $events, $getPrices, false);
    }

    protected static function getCachedEvents( $getPrices = false )
    {
      $key = $getPrices ? 1 : 0;
      if ( isset( self::$events[$key] ) ) return self::$events[$key];
      return false;
    }

    protected static function setCachedEvents( $events, $getPrices = false )
    {
      $key = $getPrices ? 1 : 0;
      self::$events[$key] = $events;
      return $events; 
    }

    public static function printEvents( $getPrices = false )
    {
        $events = self::getEvents( $getPrices );

        // debug
        echo '<pre>';
        print_r($events);
        echo '</pre><br />';
        // end debug

        // print here your events..
        // I don't know if it's a string, an object, an array...
    }

}

And in your template file use just

<?php do_action('spektrix_list_events'); ?>

or

<?php do_action('spektrix_list_events', true); // getPrices = true ?>

Code is rough and untested, but should give you a direction to start.

Answer 3

If you want any function to work juhst hook it to your appropriate needs.I think in your case you want to execute function spektrix_list_events(). It is in class so use array in hooking add_action('appropriate hook',array('SpektrixPlugin','spektrix_list_events')); Hope this will help.