Passing Class Method as a Call-Back Function in WordPress

Question

I'm looking for a way to pass a class method to a call-back function parameter.

I usually use create_function() as follows but I've heard it is slow and makes it difficult to debug.

add_action('init', create_function('', '$o = new AdminPageClass;'));
class AdminPageClass {

    function __construct() {
        add_action('admin_menu', array(&$this, 'admin_menu'));  
    }
    function admin_menu() {
        add_options_page(
            'Sample Admin Page Class', 
            'Sample Admin Page Class', 
            'manage_options',
            'sample_admin-page_class', 
            array(&$this, 'admin_page'));
    }
    function admin_page() {
        ?>
        <div class="wrap">
            <h1>Hi there</h1>
            <p>Hello World!</p>
        </div>
        <?php
    }
}

Of course, it can be done with an extra function like this; however, I'd like to do it without it if possible.

add_action('init', 'load_admin_page_class');
function load_admin_page_class() {
    $o = new AdminPageClass;
}

Also, instantiating the class object prior to it makes it possible but it creates an extra line as well.

$o = new AdminPageClass;
add_action('admin_menu', array(&$o, 'admin_menu'));

class AdminPageClass {

    function admin_menu() {
        add_options_page(
            'Sample Admin Page Class', 
            'Sample Admin Page Class', 
            'manage_options',
            'sample_admin-page_class', 
            array(&$this, 'admin_page'));
    }
    function admin_page() {
        ?>
        <div class="wrap">
            <h1>Hi there</h1>
            <p>Hello World!</p>
        </div>
        <?php
    }
}

I always define classes in separate files so I prefer the first method which reduces lines in the main plugin file. But as mentioned, use of create_function() should be avoided.

I appreciate your information.

Answer 1

I found that there was no need to create a static method at all.

add_action('admin_menu', array(new AdminPageClass, "admin_menu"));

class AdminPageClass {

    function admin_menu() {
        add_options_page(
            'Sample Admin Page Class', 
            'Sample Admin Page Class', 
            'manage_options',
            'sample_admin_page_class', 
            array(&$this, 'admin_page'));
    }
    function admin_page() {
    ?>
        <div class="wrap">
            <h1>Hi there</h1>
            <p>Hello World!</p>
        </div>
    <?php
    }       
}