Drupal multi-form loses state on page refresh

Question

I have a multi-page form. Visit page 1, page 2 and then page 3. Push refresh (f5) and the form goes back to page 2.

This is with drupal-6. The problem looks similar to this http://drupal.org/node/1060290.

Digging into the problem, via the form_cache database table. Both page 1 and 2 data appear in there. In the php debugger it looks as though a new form_id has been created. ie. storage_form-1add3819cbea88139679819935a69686 is the key in the database cache table and form-bcf9556f57f5352a57dfbba4c2120ee7 is the 'form_id' on refresh.

What does my form code look like?

Main form function:

function myform_online(&$form_state) {
  // $form_state['storage']['step'] keeps track of what page we're on.
  // start at step 1 if no storage has been set
  if (!isset($form_state['storage']['step'])) {
    $form_state['storage']['step'] = 1;
 }

 // If we are saving the form data we should submit rather than display the details.
 // At least look at saving the step.

 // Don't lose our old data when returning to a page with data already typed in.
 $default_values = array();
 if (isset($form_state['storage']['values'][$form_state['storage']['step']])) {
    $default_values = $form_state['storage']['values'][$form_state['storage']['step']];
 }

 switch ($form_state['storage']['step']) {
    case 1:
        // Your Details
        module_load_include('inc', 'join_online', 'includes/step1'); 

And we handle submit:

function join_online_submit($form, &$form_state) {
//Save the values for the current step into the storage array.
//dsm($form_state); 

$form_state['storage']['values'][$form_state['storage']['step']] = $form_state['values'];

# ahah - bail.
if ($form_state['ahah_submission']) {
    return;
}

// How do we work out if this was a refresh? It currently does start with 1 and think that the step is #2. 

//Check the button that was clicked and change the step.
if ($form_state['clicked_button']['#id'] == 'edit-previous') {
    $form_state['storage']['step']--;
} elseif ($form_state['clicked_button']['#id'] == 'edit-next') {
    $form_state['storage']['step']++;
} elseif ($form_state['clicked_button']['#id'] == 'edit-finish') {
    //You should store the values from the form in the database here.
    //We must do this or the form will rebuild instead of refreshing.
    unset($form_state['storage']);

    //Go to this page after completing the form.
    $form_state['redirect'] = 'join_online/form/thank-you';
}
}

Answer 1

If you use $form_state['rebuild'] = TRUE in _submit function the state of the form is saved and can be used for default values.

Check this example: http://www.ferolen.com/blog/how-to-create-multistep-form-in-drupal-6-tutorial/