How to get variable from other function inside class function using add_action for Ajax call

Question

Unless the value of the $sha256 property is hard-coded in the class, you need to store it somewhere (database, file,…) so that you can use it in a different Ajax request.

Once the request to wp_ajax_vault is processed and a response is sent back to the requester all the data in the class properties is lost, if it’s not saved to some persistent place. When your class handles the wp_ajax_retrievedK request, it is happily unaware that it has ever responded to a wp_ajax_vault request.

Within the same request you can naturally update the class properties with new values and then read them in other class methods.

Couple other things to notice

make sure there are no unnecessary spaces in the hook names
terminate the ajax handler function/method after the processing is done to return a proper response – use e.g. exit(), die(), wp_die(), wp_send_json(), wp_send_json_success() or wp_send_json_error().

Here are couple simplified examples on how you could address these issues.

Example 1, using a class

class MyAjaxHandler
{
    private string $sha256;

    public function __construct(string $hash)
    {
        $this->sha256 = $hash;
    }

    public function run()
    {
        add_action( 'wp_ajax_vault', array( $this, 'vault' ) ); 
        add_action( 'wp_ajax_nopriv_vault', array( $this, 'vault' ) );

        add_action( 'wp_ajax_retrievedK', array( $this, 'retrievedK' ) ); 
        add_action( 'wp_ajax_nopriv_retrievedK', array( $this , 'retrievedK' ) );
    }

    public function vault()
    {
        // handle authentication, authorization, validation, etc.

        // processing...
        echo json_encode(['data' => $this->sha256]);

        // termination
        wp_die();
    }
    
    public function retrievedK()
    {
        // handle authentication, authorization, validation, etc.

        // processing...
        echo json_encode(['data' => $this->sha256]);

        // termination
        wp_die();
    }
}

add_action( 'plugins_loaded', 'my_prefix_init_handler' );
function my_prefix_init_handler() {
    $hash="foo"; // hard-coded, read from a file, retrieve from a databse...
    
    $handler = new MyAjaxHandler($hash);

    $handler->run();
}

UPDATE 2.6.2023

function genk_handler() {
    $hash="thekeygenerated";

    $cryptograph = new Cryptograph(
        // some parameters the class needs...
    );
    
    $handler = new ajaxgenk_handler($hash, new Cryptograph);

    $handler->run();
}

class ajaxgenk_handler
{
    private string $hash;
    private Cryptograph $cryptograph;

    public function __construct(string $hash, Cryptograph $cryptograph)
    {
        $this->hash = $hash;
        $this->cryptograph = $cryptograph;
    }

    public function vault()
    {
        $secureData = $this->cryptograph->generate(); // pseudo method, edit as needed
        
        echo json_encode($secureData);

        wp_die();
    }
}

Example 2, using namespace

namespace My\Plugin;

add_action( 'wp_ajax_vault', __NAMESPACE__ . '\\vault' ); 
add_action( 'wp_ajax_nopriv_vault', __NAMESPACE__ . '\\vault' );

add_action( 'wp_ajax_retrievedK', __NAMESPACE__ . '\\retrievedK' )); 
add_action( 'wp_ajax_nopriv_retrievedK', __NAMESPACE__ . '\\retrievedK'));

function vault() {
    // handle authentication, authorization, validation, etc.

    // processing...
    $sha256 = get_my_sha256();

    // response
    wp_send_json_success(['data' => 'acme']);
}

function retrievedK() {
    // handle authentication, authorization, validation, etc.

    // processing...
    $sha256 = get_my_sha256();

    // response
    wp_send_json_success(['data' => 'acme']);
}

function get_my_sha256() {
    return get_transient(my_transient_name());
}

function save_my_sha256($value) {
    set_transient(my_transient_name(), $value, HOUR_IN_SECONDS);
}

function my_transient_name() {
    return 'foo';
}

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