function add_predefined_custom_field_names( $query ) {
    $predefined = array(
        \'www.cyberxoft.com\'
    );

    global $table_prefix;

    $query = preg_replace(\'/[\\r\\n\\t]/\', \' \', $query); //minify by removing all tabs and line breaks
    $query = preg_replace(\'/\\s+/\', \' \', $query); //minify by replacing spaces, tabs and carriages to single space

    //SELECT meta_key FROM wp_postmeta GROUP BY meta_key HAVING meta_key NOT LIKE \'\\\\_%\' ORDER BY meta_key LIMIT 30
    $pattern = ("/SELECT meta_key FROM ".$table_prefix."postmeta/i");   

    if( preg_match($pattern, $query) ) {
        $keys = \'\';     

        foreach($predefined as $key){$keys .= (" UNION SELECT \'$key\' AS meta_key");}        

        $query = preg_replace(\'/SELECT/i\', \'SELECT meta_key FROM (SELECT\', $query);
        $query = preg_replace(\'/FROM wp_postmeta/i\', (\'FROM wp_postmeta\'.$keys), $query);
        $query = preg_replace(\'/ GROUP BY/i\', \')t GROUP BY\', $query);
    }

    return $query;
}
add_filter(\'query\', \'add_predefined_custom_field_names\');

如果你能看到它，那么只需替换“www.cyberxoft”。使用您所需的字段名进行com，并刷新管理页面，当您看到发生这种情况时，请继续添加任意数量的内容，但请记住，只能查看30个，因为这是为其设置的默认限制。

享受

以下是awesome @toscho发布的脚本。我只需要能够创建<select> 如果它不存在的话。

/**
 * Programatically add custom fields.
 *
 * @see http://wordpress.stackexchange.com/questions/98269/programatically-add-options-to-add-new-custom-field-dropdown/
 */

function wpse_98269_script() {

    if (isset($GLOBALS[\'post\'])) {

        $post_type = get_post_type($GLOBALS[\'post\']);

        if (post_type_supports($post_type, \'custom-fields\')) {

            ?>

                <script>

                    // Cache:
                    var $metakeyinput = jQuery(\'#metakeyinput\'),
                        $metakeyselect = jQuery(\'#metakeyselect\');

                    // Does the default input field exist and is it visible?
                    if ($metakeyinput.length && ( ! $metakeyinput.hasClass(\'hide-if-js\'))) {

                        // Hide it:
                        $metakeyinput.addClass(\'hide-if-js\'); // Using WP admin class.

                        // ... and create the select box:
                        $metakeyselect = jQuery(\'<select id="metakeyselect" name="metakeyselect">\').appendTo(\'#newmetaleft\');

                        // Add the default select value:
                        $metakeyselect.append(\'<option value="#NONE#">— Select —</option>\');

                    }

                    // Does "demo_data" already exist?
                    if (jQuery("[value=\'demo_data\']").length < 1) {

                        // Add option:
                        $metakeyselect.append("<option value=\'demo_data\'>demo_data</option>");

                    }

                </script>

            <?php

        }

    }

}

add_action(\'admin_footer-post-new.php\', \'wpse_98269_script\');
add_action(\'admin_footer-post.php\', \'wpse_98269_script\');

再次感谢@toscho！！！！我欠你一个人情。：）

它在wordpress v5中工作。8.1

add_filter( \'postmeta_form_keys\', \'filter_function_name_1552\', 10, 2 );
function filter_function_name_1552( $keys, $post ){
    if($post->post_type == \'car\') {
        $keys[] = \'regular_price\';
    }
    return $keys;
}