source: sipes/modules_contrib/views/help/api-forms.html @ 65dadeb

Views allows handlers to output form elements, wrapping them automatically in a form, and handling validation / submission.
The form is multistep by default, allowing other modules to add additional steps, such as confirmation screens.

<h2>Implementation</h2>
A views handler outputs a special placeholder in render(), while the real form with matching structure gets added in views_form().
When the View is being preprocessed for the theme file, all placeholders get replaced with the rendered form elements.

The views handler can also implement views_form_validate() and views_form_submit().
<pre>
  function render($values) {
    return '&lt;!--form-item-' . $this-&gt;options['id'] . '--' . $this-&gt;view-&gt;row_index . '--&gt;';
  }

  function views_form(&$form, &$form_state) {
    // The view is empty, abort.
    if (empty($this-&gt;view-&gt;result)) {
      return;
    }

    $field_name = $this-&gt;options['id'];
    $form[$field_name] = array(
      '#tree' => TRUE,
    );
    // At this point, the query has already been run, so we can access the results
    foreach ($this-&gt;view-&gt;result as $row_id => $row) {
      $form[$field_name][$row_id] = array(
        '#type' => 'textfield',
        '#title' => t('Your name'),
        '#default_value' => '',
      );
    }
  }

  // Optional validate function.
  function views_form_validate($form, &$form_state) {
    $field_name = $this-&gt;options['id'];
    foreach ($form_state['values'][$field_name] as $row_id => $value) {
      if ($value == 'Drupal') {
        form_set_error($field_name . '][' . $row_id, "You can't be named Drupal. That's my name.");
      }
    }
  }

  // Optional submit function.
  function views_form_submit($form, &$form_state) {
    // Do something here
  }
</pre>

Modules can implement hook_views_form_validate($form, &$form_state) and hook_views_form_submit($form, &$form_state).

The form is multistep by default, with one step: 'views_form_views_form'.
A "form_example" module could add a confirmation step by setting:
<pre>
 $form_state['storage']['step'] = 'form_example_confirmation';
</pre>
in form_example_views_form_submit().
Then, views_form would call form_example_confirmation($form, $form_state, $view, $output) to get that step.

<b>Important:</b> You can fetch the Views object in form_alter and validate / submit hooks from $form['#parameters']:
<pre>
  $view = $form['#parameters'][2];
</pre>

<h2>Relevant Views functions</h2>
<ul>
<li>template_preprocess_views_view()</li>
<li>views_form()</li>
<li>views_form_validate()</li>
<li>views_form_submit()</li>
<li>views_form_views_form()</li>
<li>views_form_views_form_validate()</li>
<li>views_form_views_form_submit()</li>
<li>theme_views_form_views_form()</li>
</ul>

<h2>Hooks</h2>
<ul>
<li>hook_views_form_substitutions()</li>
<li>hook_views_form_validate($form, &$form_state)</li>
<li>hook_views_form_submit($form, &$form_state)</li>
</ul>