Undefined index in Wordpress plugin when call AJAX - php

Question

I created plugin for Wordpress and am now trying to learn Ajax in plugin.
When I call my function:
wp-admin/admin-ajax.php?action=my_action
I get this error:
Notice: Undefined index: whatever
This is my function
add_action( 'admin_footer', 'my_action_javascript' ); // Write our JS below here
function my_action_javascript() { ?>
<script type="text/javascript" >
jQuery(document).ready(function($) {
var data = {
'action': 'my_action',
'whatever': 1234
};
// since 2.8 ajaxurl is always defined in the admin header and points to admin-ajax.php
$.post(ajaxurl, data, function(response) {
alert('Got this from the server: ' + response);
});
});
</script> <?php
}
and function call back
add_action( 'wp_ajax_my_action', 'my_action_callback' );
function my_action_callback() {
global $wpdb; // this is how you get access to the database
$whatever = intval( $_POST['whatever'] );
$whatever += 10;
echo $whatever;
wp_die(); // this is required to terminate immediately and return a proper response
}
What's causing this error and how can I fix it?

Answer 1

When you make a request to wp-admin/admin-ajax.php?action=my_action it only includes the action query string parameter and not the whatever parameter that the callback function in WordPress is expecting.
If you want this to work in a browser test from the address bar replace $_POST['whatever'] with $_REQUEST['whatever'] and use this in your browser wp-admin/admin-ajax.php?action=my_action&whatever=1234 - this will pass whatever as a GET whereas in your ajax it is a POST, but $_REQUEST will see both.
That said, your example code is correct - I even tested it on a local install. When your JavaScript executes it will include both parameters as part of the data object, which can then be process in the ajax handler. Just load your site in a browser and the code should alert unless you have other JavaScript errors.