WordPress的admin-ajax.php

Question

I have a Wordpress admin-ajax.php problem: First my WordPress admin-ajax.php returns 0 and now it's a clean sheet.

I already changed:

// Require an action parameter
if ( empty( $_REQUEST['action'] ) )
    die( );

to

// Require an action parameter
if ($_REQUEST['action'] == 'crop_apply_header_image') {
   var_dump($_REQUEST);
   die();

My compleet admin-ajax.php:

<?php
/**
 * WordPress Ajax Process Execution
 *
 * @package WordPress
 * @subpackage Administration
 *
 * @link https://codex.wordpress.org/AJAX_in_Plugins
 */

/**
 * Executing Ajax process.
 *
 * @since 2.1.0
 */
define( 'DOING_AJAX', true );
if ( ! defined( 'WP_ADMIN' ) ) {
    define( 'WP_ADMIN', true );
}

/** Load WordPress Bootstrap */
require_once( dirname( dirname( __FILE__ ) ) . '/wp-load.php' );

/** Allow for cross-domain requests (from the front end). */
send_origin_headers();

// Require an action parameter
if ($_REQUEST['action'] == 'crop_apply_header_image') {
   var_dump($_REQUEST);
   die();
}

/** Load WordPress Administration APIs */
require_once( ABSPATH . 'wp-admin/includes/admin.php' );

/** Load Ajax Handlers for WordPress Core */
require_once( ABSPATH . 'wp-admin/includes/ajax-actions.php' );

@header( 'Content-Type: text/html; charset=' . get_option( 'blog_charset' ) );
@header( 'X-Robots-Tag: noindex' );

send_nosniff_header();
nocache_headers();

/** This action is documented in wp-admin/admin.php */
do_action( 'admin_init' );

$core_actions_get = array(
    'fetch-list', 'ajax-tag-search', 'wp-compression-test', 'imgedit-preview', 'oembed-cache',
    'autocomplete-user', 'dashboard-widgets', 'logged-in',
);

$core_actions_post = array(
    'oembed-cache', 'image-editor', 'delete-comment', 'delete-tag', 'delete-link',
    'delete-meta', 'delete-post', 'trash-post', 'untrash-post', 'delete-page', 'dim-comment',
    'add-link-category', 'add-tag', 'get-tagcloud', 'get-comments', 'replyto-comment',
    'edit-comment', 'add-menu-item', 'add-meta', 'add-user', 'closed-postboxes',
    'hidden-columns', 'update-welcome-panel', 'menu-get-metabox', 'wp-link-ajax',
    'menu-locations-save', 'menu-quick-search', 'meta-box-order', 'get-permalink',
    'sample-permalink', 'inline-save', 'inline-save-tax', 'find_posts', 'widgets-order',
    'save-widget', 'delete-inactive-widgets', 'set-post-thumbnail', 'date_format', 'time_format',
    'wp-remove-post-lock', 'dismiss-wp-pointer', 'upload-attachment', 'get-attachment',
    'query-attachments', 'save-attachment', 'save-attachment-compat', 'send-link-to-editor',
    'send-attachment-to-editor', 'save-attachment-order', 'heartbeat', 'get-revision-diffs',
    'save-user-color-scheme', 'update-widget', 'query-themes', 'parse-embed', 'set-attachment-thumbnail',
    'parse-media-shortcode', 'destroy-sessions', 'install-plugin', 'update-plugin', 'press-this-save-post',
    'press-this-add-category', 'crop-image', 'generate-password', 'save-wporg-username', 'delete-plugin',
    'search-plugins', 'search-install-plugins', 'activate-plugin', 'update-theme', 'delete-theme',
    'install-theme', 'get-post-thumbnail-html', 'get-community-events',
);

// Deprecated
$core_actions_post[] = 'wp-fullscreen-save-post';

// Register core Ajax calls.
if ( ! empty( $_GET['action'] ) && in_array( $_GET['action'], $core_actions_get ) )
    add_action( 'wp_ajax_' . $_GET['action'], 'wp_ajax_' . str_replace( '-', '_', $_GET['action'] ), 1 );

if ( ! empty( $_POST['action'] ) && in_array( $_POST['action'], $core_actions_post ) )
    add_action( 'wp_ajax_' . $_POST['action'], 'wp_ajax_' . str_replace( '-', '_', $_POST['action'] ), 1 );

add_action( 'wp_ajax_nopriv_heartbeat', 'wp_ajax_nopriv_heartbeat', 1 );

if ( is_user_logged_in() ) {
    /**
     * Fires authenticated Ajax actions for logged-in users.
     *
     * The dynamic portion of the hook name, `$_REQUEST['action']`,
     * refers to the name of the Ajax action callback being fired.
     *
     * @since 2.1.0
     */
    do_action( 'wp_ajax_' . $_REQUEST['action'] );
} else {
    /**
     * Fires non-authenticated Ajax actions for logged-out users.
     *
     * The dynamic portion of the hook name, `$_REQUEST['action']`,
     * refers to the name of the Ajax action callback being fired.
     *
     * @since 2.8.0
     */
    do_action( 'wp_ajax_nopriv_' . $_REQUEST['action'] );
}
// Default status
die( );

I tried the answers on stackoverflow but still no reaction. Can you help me please :)

Cheers,

Johan