Question

I’m updating a module I’ve written from D6 to D7, and therefore have to exchange the old AHAH by the new #ajax in forms.

I’m performing an ajax request which creates a result and replaces a form element with it. This basically works fine, but after the first request, the result is cached and does not take changes in the form into account. I think this is probably a browser-issue, but could it be that Drupal sends an expiration header which induces the browser to take the cached version? Ot any other ideas?

The fragment in hook_cache():

  $form['fieldset']['mybutton'] = array(
    '#type' => 'button',   
    '#value' => t('Send request'),
    '#ajax' => array(
          'callback' => 'mycallback',
          'wrapper' => 'mywrapper',
          'method' => 'replace',
          'effect' => 'fade',  
    )

A snippet of the callback:

function mycallback($form, $form_state) {

        [..]

        $form['fieldset']['mywrapper']['#markup'] = 'test';
        return $form['fieldset']['mywrapper']['#markup'];
    }

Answer 1

I’ve run into this problem a few times and it isn’t a caching issue. The problem is you’ll originally have a <div> wrapped around your mywrapper element, but in your ajax callback you’re replacing it with a string…the <div> wrapper is therefore replace and next time you press the button the script can’t find the <div> it needs to replace as it’s not there any more!

Also, the arguments for your mycallback function need to be passed in by reference so change the signature to this: function mycallback(&$form, &$form_state) {.

Try making your code look a bit more like this:

function mymodule_my_form($form, &$form_state) {
  $form['fieldset'] = array(
    '#type' => 'fieldset'
  );

  $form['fieldset']['my_element'] = array(
    '#markup' => 'Some initial markup',
    '#prefix' => '<div id="mywrapper">',
    '#suffix' => '</div>'
  );

  $form['fieldset']['mybutton'] = array(
    '#type' => 'button',   
    '#value' => t('Send request'),
    '#ajax' => array(
      'callback' => 'mymodule_mycallback',
      'wrapper' => 'mywrapper',
      'method' => 'replace',
      'effect' => 'fade',  
    )
  );

  return $form;
}


function mymodule_mycallback(&$form, &$form_state) {
  $form['fieldset']['my_element']['#markup'] = 'New Markup';

  // Always, always, always return an element here, not a string.
  // This makes sure the form state stays consistent.
  return $form['fieldset']['my_element'];
}

If in doubt have a look at the examples module, specifically the ajax_example_submit_driven_ajax() example in the ajax_example module.