link_field_custom_form_test.module

<?php
/**
 * @file
 * Helper module for testing link fields with custom forms.
 */

/**
 * Implements hook_menu().
 */
function link_field_custom_form_test_menu() {
  $items['link-field-custom-form'] = array(
    'title' => "Custom Form to test link field",
    'page callback' => 'backdrop_get_form',
    'page arguments' => array('link_field_custom_form_test_form'),
    'access callback' => TRUE,
    'type' => MENU_CALLBACK,
  );

  return $items;
}

/**
 * Custom form for testing link field.
 *
 * @param array $form
 *   The form array.
 * @param array $form_state
 *   The form state array.
 *
 * @see link_field_custom_form_test_menu()
 *
 */
function link_field_custom_form_test_form(array $form, array &$form_state) {
  $form = array();
  $form['link_test_defaults'] = array(
    '#type' => 'link_field',
    '#title' => t('Link defaults'),
    '#required' => TRUE,
  );
  $form['link_test_title_changes'] = array(
    '#type' => 'link_field',
    '#title' => t('Link with title changed'),
    '#link_field_options' => array(
      'title_maxlength' => 16,
      'title_label_use_field_label' => TRUE,
    ),
  );
  $form['link_test_internal_no_title'] = array(
    '#type' => 'link_field',
    '#title' => t('Link without title'),
    '#link_field_options' => array(
      'title_mode' => 'none',
      'link_type' => 'internal',
    ),
  );
  $form['link_test_validate_url'] = array(
    '#type' => 'link_field',
    '#title' => t('Required link with URL validation'),
    '#required' => TRUE,
    '#link_field_options' => array(
      'url_mode' => 'required',
      'title_mode' => 'required',
      'validate_url' => TRUE,
    ),
    '#default_value' => array(
      'title' => 'Example title on custom link field',
      'url' => 'http://example.com',
    ),
  );
  $form['configurable_title_and_class'] = array(
    '#type' => 'link_field',
    '#title' => t('Link with configurable title and class'),
    '#link_field_options' => array(
      'configurable_title' => TRUE,
      'configurable_class' => TRUE,
    ),
  );
  $form['submit'] = array(
    '#type' => 'submit',
    '#value' => t('Submit'),
  );
  return $form;
}

/**
 * Form submission handler for link_field_custom_form_test_form().
 */
function link_field_custom_form_test_form_submit(array $form, array &$form_state) {
  $output = print_r($form_state['values'], TRUE);
  $output = str_replace(array("\r", "\n"), '', $output);
  $output = str_replace(array("    ", "   ", "  "), ' ', $output);
  backdrop_set_message($output);
}