piklist-filter-piklist_validation_rules-callback

<?php

  // Create a validation rule called "my_file_exists"

  add_filter('piklist_validation_rules', 'check_file_exists', 11);
  function check_file_exists($validation_rules)
  {
    $validation_rules['my_file_exists'] = array(
      'callback' => 'my_validate_file_exists'
    );
   
    return $validation_rules;
  }
  
  
  /**
   * @param int $index The field index being checked.
   * @param mixed $value The value of the field.
   * @param array $options The options.
   * @param array $field The field object.
   * @param array $fields Collection of fields.
   */
  function my_validate_file_exists($index, $value, $options, $field, $fields)
  {
    return @file_get_contents($value) ? true : 'contains a file that does not exist.';
  }