Plugin function inside custom plugin

Question

I am trying to use a plugin function ( wp-bannerize() ) inside my custom plugin. but when i write:

if( function_exists('wp_bannerize') ){
            echo "exist";
        }else{
            echo "not exist";
        } 

The output is not exists

How can i get this function inside my custom plugin?

UPDATE:

Here the code of my plugin:

class Infinite_posts{

    public function __construct() { 

        add_action('wp_ajax_is_bannerize', 'load_plugins');
//when plugin receive an AJAX call with 'is_bannerize'parameter load_plugins() is triggered

    }

    public function load_plugins(){
        add_action( 'plugins_loaded', 'show_bannerize' );
//when all plugin are loaded show_bannerize() is triggered
    }

    public function show_bannerize(){
        if( function_exists( 'wp_bannerize' ) ) {
            echo "exist";
        } else {
            echo "not exist";
        }       
    }
}

if( !is_admin() )
    $infinitePosts = new Infinite_posts();

here my javascript too:

$('.gallerie h2').on('click', function(){
  jQuery.post(
      'http://localhost/~sdibenedetto/d-art/htdocs/wp-content/plugins/infinite-posts/infinite-posts.php', 
      {
          'action': 'is_bannerize',
          'data':   'foobarid'
      }, 
      function(response){
          alert('The server responded: ' + response);
      }
  );

});

Is this correct? How to make the AJAX call and pass the parameter "is_bannerize" to trigger the plugin? With this javascript i have this error in the alert:

<b>Fatal error</b>:  Call to undefined function add_action() in <b>/Users/sdibenedetto/Sites/d-art/htdocs/wp-content/plugins/infinite-posts/infinite-posts.php</b> on line <b>44</b><br />

Pls help. Thanks

Answer 1

You're probably making the check too early. Make sure all plugins are loaded before trying to access the methods they provide. You can hook into plugins_loaded action to make sure all plugins are loaded before trying to use the functions they define.

class My_Plugin {
    public static function init() {
        if( function_exists( 'wp_bannerize' ) ) {
            echo "exist";
        } else {
            echo "not exist";
        } 
    }
    public function __construct() { ... }
}
add_action( 'plugins_loaded', array ( 'My_Plugin', 'init' ), 10 );

Answer 2

Your syntax is wrong. You cannot hook object methods like this:

add_action('wp_ajax_is_bannerize', 'load_plugins');

You need to hook them like this:

add_action('wp_ajax_is_bannerize', array($this,'load_plugins'));

I am puzzled how you get output at all.

Secondly, you are calling the plugin file directly. Don't do that. Loading a file by a direct URL like this-- http://localhost/~sdibenedetto/d-art/htdocs/wp-content/plugins/infinite-posts/infinite-posts.php-- will cause the file to load outside of a WordPress context. You will have all kinds of "undefined function" errors and other functionality problems. Your class appears to be trying to use the AJAX API but your Javascript is not. You need to use the API.

Correct those issues and come back if there are still other problems.