Wordpress class, using add_action to call member function does not work

Question

I'm learning to create a WP plugin as a class. However, it seems the add_action doesn't work when calling my function; it works when using $this->init().

Example:

    class test
{

    public $age = NULL;

    public function __construct()
    {
        //register an activation hook
        register_activation_hook( __FILE__, array( &$this, 'installplugin' ) );

        add_action('init', array( &$this, 'init' ) ); //this doesn't work
        //$this->init(); //This WORKS!

    }

    function installplugin()
    {

        add_option( 'age', 45 );
        $this->init();  

    }

    function init()
    {

        $age = get_option( 'age' );
        $this->age = $age;



    }

    function printAge(  )
    {
        echo "The age is " . $this->age . "<br />";
    }

}

So, after running:

$learnObj =  new learnable_test();

$learnObj->printAge();

It only prints: "The age is "

But if I were t comment out the add_action('init',...) and use the $this->init(), that seems to work, printing "The age is 45"

What am I missing?

Answer 1

Well it can't and won't work like you want it to.

Let's look at what exactly are you doing.

Inside your constructor you have:

add_action('init', array( &$this, 'init' ) ); //this doesn't work

So you add init method of your object to WPs init hook. When WP runs it's init action, then your init method will be run to, but not sooner and not later.

Then you do something like this:

$learnObj =  new learnable_test();

$learnObj->printAge();

So you create object of your class. It will add $learnObj->init to WPs init hook.

If you call these 2 lines after WPs init hook was already done, nothing will happen.

If you call them before (I guess you do) - your $learnObj->init will be executed during WPs init action (and age variable will be set).

But in the second line you want to access this age variable. It won't be set here yet, because WP haven't yet executed it's init action, thus your $learnObj->init hasn't been executed too.