Drupal 6 multistep form example

I had a very hard time making a Drupal multistep form finding an example which wasn't trying to be clever. So when I had a nasty problem I made my own multistep_example module to help debug. the bug by the way turned out to be with the hide_submit module disable mode, which breaks when there are two submit buttons.

The following code attempts to make the simplest possible Drupal 6 multistep form, including submit and validate functions. Use it as the basis for your multistep form. The only issue is that #redirect doesn't work, so drupal_goto is used instead. Here is the module code in its entirety:

 'Multistep example',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('multistep_example_form'),
    'access callback' => TRUE
  );
  return $items;
}

function multistep_example_form($form_state) {
  if (!$form_state['storage']['step']) $form_state['storage']['step'] = 1;
  $form_state['values'] = $form_state['storage']['values'];
  drupal_set_title('Multistep example - step '. $form_state['storage']['step'] . ' of '. STEPS);

  $form = array();
  //'next' appears at every step
  $form['next'] = array(//corresponds to 'edit-next' in form_submit
    '#type' => 'submit',
    '#value' => 'submit',
    '#weight' => 1
  );
  switch($form_state['storage']['step']) {
    case 1:
      $form['info1'] = array(
        '#title' => 'field on first page',
        '#type' => 'textfield',
        '#default_value' => $form_state['values']['info1'],
        '#element_validate' => array('multistep_element_validate'),
      );
    break;
    case 2:
      $form['info2'] = array(
        '#title' => 'field on second page',
        '#type' => 'textfield',
        '#default_value' => $form_state['values']['info2'],
        '#element_validate' => array('multistep_element_validate'),
      );
    
  }
  //next button
  if ($form_state['storage']['step'] > 1) {
    $form['back'] = array( //corresponds to 'edit-back' in form_submit
      '#value' => 'back',
      '#type' => 'submit',
      '#weight' => 1
    );
  }

  $form['#redirect'] = 'user';
  return $form;
}

function multistep_example_form_submit(&$form, &$form_state) {
  //multistep processing
  if (!$form_state['storage']['values']) {
    $form_state['storage']['values'] = array();
  }
  //increment the button, overwrite the storage values with the new values, and return
  if ($form_state['clicked_button']['#id'] == 'edit-back') {
    $form_state['storage']['step']--;
    $form_state['storage']['values'] = $form_state['values'] + $form_state['storage']['values'];
    return;
  } elseif ($form_state['clicked_button']['#id'] == 'edit-next' && $form_state['storage']['step'] < STEPS) {
    $form_state['storage']['step']++;
    $form_state['storage']['values'] = $form_state['values'] + $form_state['storage']['values'];
    return;
  }
  
  //if this is the last step,
  $values = $form_state['storage']['values'] + $form_state['values'];
  //clear the storage and rebuild so that the fom doesn't rebuild, and the #redirect works
  $form_state['rebuild'] = TRUE;
  unset($form_state['storage']);

  $values = $form_state['storage']['values']['info1'] .' & '. $form_state['storage']['values']['info2'];
  drupal_set_message('The form has been submitted with values: '.$values);
}


function multistep_example_form_validate($form, &$form_state) {
  drupal_set_message('validating multistep form');
}

function multistep_element_validate($element, &$form_state) {
  drupal_set_message('validating field: '. $element['#name']);
}