我的自定义函数：

/**
 * Prints out one specified field from settings section.
 *
 * Based on:
 * @see do_settings_sections
 * 
 * @global array $wp_settings_sections  Storage array of all settings sections added to admin pages
 * @global array $wp_settings_fields    Storage array of settings fields and info about their pages/sections
 *
 * @param string $page                  The slug name of the page whose settings sections you want to output
 * @param string $field_id              Field ID for output
 */
public static function do_settings_section_field($page, $field_id) {
    global $wp_settings_sections, $wp_settings_fields;

    if ( ! isset( $wp_settings_sections[$page] ) )
        return;

    foreach ( (array) $wp_settings_sections[$page] as $section ) {

        if ( $section[\'callback\'] )
            call_user_func( $section[\'callback\'], $section );

        if ( ! isset( $wp_settings_fields[$page][$section[\'id\']] ) )
            continue;

        foreach ( (array) $wp_settings_fields[$page][$section[\'id\']] as $field ) {
            if ( $field[\'id\'] !== $field_id )
                continue;

            call_user_func($field[\'callback\'], $field[\'args\']);
        }
    }
}