Class property not visible inside ajax callback function?

Question

I have a class that has ajax callbacks inside it, as well as actions set in the __construct() of that class. I am also passing the property to the class when instantiating it. It looks kinda like this

<?php

class My_Class{

    private $passed_string;

    public function __construct( $passed_string ) {
        $this->$passed_string = $passed_string;

        add_action( 'wp_ajax_my_callback', array( $this, 'my_callback' ) );
    }

    public function my_callback() {

        error_log( print_r( $this->$passed_string, true ) );
        wp_die();
    }

}

$init = new My_Class( 'Passed string!' );

Now this should show in my error logs when I call this function with ajax. But it's empty.

The callback works (tested).

The thing is that when doing this in a similar class that has a method inside, that is not hooked to wp_ajax hook it works, and I see the passed string just fine.

How come?

Answer 1

Have you used AJAX before? Do you know what the acronym stands for? Hint: The J stands for javascript. Indeed, AJAX is usually invoked using javascript/jQuery. I believe that's why you're not receiving a response: you aren't invoking an AJAX protocol or going through Wordpress's admin-ajax.php.

And, why would you put a callback function in a constructor in the first place?