FAPI Loads Wrong Form When Re-Submitting Multi-step Form

Interesting... No, it looks like it's FAPI not theming (unless there's something really wierd going on - the testcase doesn't do any clever theming). Say you have something like:

function testcase_menu($may_cache) {
  $items = array();
  if($may_cache) {
    $items[] = array(
      'path' => 'testcase',
      'title' => t('FAPI Test Case'),
      'description' => t('Demonstrate A Problem with Checkboxes'),
      'callback' => 'drupal_get_form',
      'callback arguments' => 'testcase_form',
      'access' => user_access('use testcase module'),
      'type' => MENU_NORMAL_ITEM,
    );
  }
  return $items;
}

...then you'd expect a function called "testcase_form" to be called with $form_values either set to NULL or as an array. If an array, then it ought to include all the values posted on the last submit from the user. That array seems to be incomplete (well, empty), so FAPI ends up loading the wrong form, which then means it's not possible to validate/submit the data. As I say, it only seems to happen after a validation failure (first submit works just fine, so long as you make no mistakes).

All form elements need a bit of thinking about across multistep forms, but most can be manipulated by correcting #default_value (except checkboxes). Given this FAPI issue, avoid textfield and textarea elements, because they'll need more careful validation than is possible (actually, if you put all your text elements on page 1, you could work around this issue)

I personally haven't used hook_form or hook_validate - my forms are all standalone, so generate whole forms themselves, not as part of some other node module.

I agree about patching up 5.1. I've had a look at FAPI (for the checkbox issue above) and concluded I couldn't make it work. Having had another look, I can't immediately see how/why the wrong form gets loaded in this case either. I'll keep looking, and obviously will post a patch if I get anywhere.

That said, keep an eye on Pre-Emptive's Website - I have a funny feeling that wizard.module will appear there soon (even though it's got limited use on Drupal 5.1) ;-)

I'm 99% certain this is solved in Drupal 6. I've attached a testcase which shows it working. I'm a little nervous however, because the testcase is pretty simple, and my application is pretty complex - until I've tested that, I'm a bit scared of commitment ;-) I'll be a while, but I'll confirm when I know.

This looks a lot like anothe thread (which I didn't find before I started this one!).

Multi Part forms after failing validate function, return to first step on submit.

I'm reluctant to confirm beyond all doubt, but certainly, I have had a more complex form running on D6 and it works as expected.

So yes, I think this is fixed in Drupal 6. I am aware of other FAPI issues in D6 (which don't appear to be getting fixed), which may have implications, so be careful.