PHP - Can't access properties declared in another method when calling methods using AJAX

Question

I apologise if this question is a bit long winded, but it's quite a large chunk of code and I cannot get it to work for the life of me...

I am building a form inside a Wordpress plugin that should gather some data (either through form inputs, API, or a combination of both - such as calling different API endpoints depending on form values). I want to then use these variables (or properties, as they seem to be referred to within classes) in different methods.

Firstly, I have my class and then a method to register my plugin on the Wordpress menu bar:

class EnigmaDMU {
    
    private $enigma_dmu_screen_name;  
    private static $instance;
  
    static function GetInstance()  
    {  
          
        if (!isset(self::$instance))  
        {  
            self::$instance = new self();  
        }  
        return self::$instance;  
    }  
    
    // This loads the WP menu page and plugin page
    public function PluginMenu() {  
     $this->enigma_dmu_screen_name = add_menu_page(  
                                      'Enigma DMU Post',   
                                      'Enigma DMU Post',   
                                      'manage_options',  
                                      __FILE__,   
                                      array($this, 'RenderPage'),   
                                      plugins_url('enigma-daily-update/assets/enigma-cube-white.svg',__DIR__)  
                                      );  
    }

I then have another method called 'RenderPage' which contains my form and the HTML elements for my plugin page inside the WP admin:

public function RenderPage(){
        ?>  
            <div class='wrap'>
                <div class="header-bar">
                    <h1>Daily Market Update</h1>
....... continued here

At the very bottom of my code, I have a method to initiate the plugin which adds the AJAX handlers (my methods) for certain AJAX actions which are called in my AJAX requests:

public function InitPlugin()  {

        add_action('admin_menu', array($this, 'PluginMenu'));
        add_action('admin_enqueue_scripts', array($this, 'dmu_load_scripts'));
        add_action('admin_enqueue_styles', array($this, 'dmu_load_scripts'));

        add_action('wp_ajax_btc_data', array($this, 'getBTCData'));
        add_action('wp_ajax_test_func', array($this, 'testFunc'));
}
} //this is the closing tag for the Class.

Underneath this, I have some class-related definitions, which admittedly I am unsure what they do - this was part of a larger tutorial I followed to set up this plugin:

$EnigmaDMUpost = EnigmaDMU::GetInstance();  
$EnigmaDMUpost->InitPlugin();  

?>

Almost there... I also have my handlers (I have included a test handler to simplify this explanation):

public function getBTCData() {

        require __DIR__."/vendor/autoload.php";
        $client = new GuzzleHttp\Client();

        $btc_curl = $client->get('https://api.alternative.me/v1/ticker/bitcoin/',);
        $btc_curl_body = $btc_curl->getBody();
        $btc_curl_body_json = json_decode($btc_curl_body);

        foreach($btc_curl_body_json as $result){
            $btc_price_ur = $result->price_usd;
            $btc_change_ur = $result->percent_change_24h;
        }

        $btc_price = round($btc_price_ur, 2);
        $btc_change = round($btc_change_ur, 2);
        $this->row3b = $btc_change . '%';

        echo 'inside: ' . $this->row3b;

        die();

    }

I am able to echo this value here (row3b) inside my plugin successfully - this works as expected.

However, when I try and call the property from my testFunc, I get nothing:

public function testFunc() {
        $test_item = $this->row3b;
        echo 'btc dominance = ' . $test_item . '%.';
    }

Finally, the relevant areas of my AJAX script are as follows:

jQuery(document).ready(function($) {
    $('#dmu_submit').click(function() {
        $('#dmu-loader').show();
        $('#dmu_submit').attr('disabled', true);

        btc_data = {
            action: 'btc_data',
            dmu_nonce: dmu_vars.dmu_nonce
        };

        $.post(ajaxurl, btc_data, function(response) {
            $('#dmu-results').html(response);
            $('#dmu-loader').hide();
            $('#dmu_submit').attr('disabled', false);
        });

    $('#dmu_test_func').click(function() {
        $('#dmu-loader').show();
        $('#dmu_submit').attr('disabled', true);

        test_data = {
            action: 'test_func',
            dmu_nonce: dmu_vars.dmu_nonce
        };

        $.post(ajaxurl, test_data, function(response) {
            $('#dmu-results-test').html(response);
            $('#dmu-loader').hide();
            $('#dmu_submit').attr('disabled', false);
        });

        return false;
    });

Any help would be massively appreciated - I know it's a long post, but I feel as if the answer is actually really simple, I just cannot figure it out. It feels as if I'm doing everything right. Thank you!!

Answer 1

It's not completely clear from your code examples which class your testfunc() is in. But $this in php refers to the instance of the class that it resides within, and the ->row3b refers to a property called row3b (a property is a variable that belongs to the class which is usually defined at the top of the class code). If you're calling $this->row3b within the class itself it will work, but if you need to refer to it from outside the class you will need to instantiate a new instance of the class, and then refer to it with the variable name you assign. E.g.

$myInstance = new theclassname(); $myInstance->row3b;

If the row3b is a static property its slightly different again, you can refer to this outside of the class as theclassname::$row3b

Edit: also ensure that the testfunc resides in the same class that the add_actions are in. The $this in the add_action tells wordpress that it should look for your handler in 'this' class.

Edit2: I think you may also need the die() at the end of your testfunc. Wordpress ajax is funny about this.