Form alter the user form with AHAH

user_register_alter_example.info

name = User register alter example
description = Demonstrates how to alter the registration form with an AHAH element.
core = 6.x

user_register_alter_example.module

<?php


function user_register_alter_example_form_user_register_alter(&$form, &$form_state) {
  // This is an example of just injecting some spare form
  $form['og_register']['x'] = user_register_alter_example_spare_form($form_state);

  // This is how to add a section with a #ahah button. It's pretty much
  // identical to the stuff in the ahah example, but it is being added
  // with a form alter.
  $form['og_register']['ahahbutton'] = array(
    '#type' => 'submit',
    '#value' => t('Add more stuff'),
    '#ahah' => array(
      'wrapper' => 'og_register_ahah_stuff',
      'path' => 'og_register_stuff',
    ),
    '#validate' => array(),
    '#submit' => array(),
  );
  $form['og_register']['where_extra_stuff_goes'] = array(
    '#prefix' => '<div id="og_register_ahah_stuff">',
    '#suffix' => '</div>',
    '#type' => 'fieldset',
  );
  if (!empty($form_state['values']['op']) && $form_state['values']['op'] == t('Add more stuff')) {
    $form['og_register']['where_extra_stuff_goes']['myselect'] = array(
      '#type' => 'select',
      '#title' => t('A select element'),
      '#options' => array('one' => 'One', 'two' => 'Two'),
    );

    // You have to add to the form submission something to work with your extra
    // form elements.
    // $form['#submit'][] = 'some_submit_function_that_will_process_extra_stuff';
  }

  // To do the above, though, I think we have to relax the #required

}
function user_register_alter_example_og_register_callback() {
  $form = user_register_alter_example_callback_helper();

  $fieldset = $form['og_register']['where_extra_stuff_goes'];
  // Remove the wrapper so we don't double it up.
  unset($fieldset['#prefix'], $fieldset['#suffix']);

  $output = theme('status_messages');
  $output .= drupal_render($fieldset);

  // Final rendering callback.
  drupal_json(array('status' => TRUE, 'data' => $output));
  exit();
}

function user_register_alter_example_spare_form(&$form_state) {
  $form['sometitle'] = array(
    '#type' => 'textfield',
    '#title' => t('This is a spare form being injected'),
  );
  return $form;
}


/**
 * Implement hook_menu().
 *
 * Note that each item has both an entry point to prepare the form, and also
 * a callback function that provides and AHAH menu callback.
 */
function user_register_alter_example_menu() {
  $items = array();

  $items['og_register_stuff'] = array(
    'page callback' => 'user_register_alter_example_og_register_callback',
    'access callback' => TRUE,
    'type' => MENU_CALLBACK,
  );

  return $items;
}

/**
 * Does the very standard things that must be done in any normal callback.
 * Used by each callback in this example module.
 */
function user_register_alter_example_callback_helper() {
  $form_state = array('storage' => NULL, 'submitted' => FALSE);
  $form_build_id = $_POST['form_build_id'];
  $form = form_get_cache($form_build_id, $form_state);
  $args = $form['#parameters'];
  $form_id = array_shift($args);
  $form_state['post'] = $form['#post'] = $_POST;
  // Enable the submit/validate handlers to determine whether AHAH-submittted.
  $form_state['ahah_submission'] = TRUE;
  $form['#programmed'] = $form['#redirect'] = FALSE;
  drupal_process_form($form_id, $form, $form_state);
  $form = drupal_rebuild_form($form_id, $form_state, $args, $form_build_id);
  return $form;
}