Form API: default value does not change

Cant you use jQuery("id).val(); to change it in the font, you are already using Javascript right?
You said everything did change correctly within the PHP, so it should just be a output problem.

Without seeing the whole function, its hard to tell where $name comes from.

My guess is that the default value is not displayed on the form so you can't change it with AJAX. The default value is just the initial value that is put into $form['name']['value'] when the form is rendered. You can probably change the default value but without re-loading the form you won't see it?

Thank you melissavdh I had been trying to figure this one out from the last hour .. :)

Had read it before in the documentation but forgot while implementing. I have been trying to alter a webform, and have noted that the fields that i had created in the form_alter function did not have this restriction but the fields that were created by the webform module did... I wonder why?

Unsetting $form_state['input']['element_name'] will work but what if form is rebuilding after failing in validations ? I think, It will again display your '#default_value', which seems wrong. It should display entered value. Any thoughts ??

I had the same problem, default value does not change on ajax load but it works when I replace #default_value with #value.

Hi all,

I looked at all your posts. In some special cases (i.e. when I receive specific url parameters), I want a checkbox field of a form to be no-editable with a default value. When I hit the form, the checkbox is greyed out and is checked (which is the default value I set). But the field value when the form is submitted is not the value I expect, as the checkbox is not checked.

I guess I only change the form when displayed, how can I also change the value of the checkbox ? Thank you.

Here is my code:

function mymodule_form_alter(&$form, &$form_state, $form_id) {
  if($form_id == 'my_form_id') {
      // set the default value to my check box
      $form['checkbox_field_name']['#default_value'][0]['value'] = 'this_will_check_the_box'; 
      // make the checkbox not-editable
      $form['#after_build'][] = '_disable_field_after_build';
  }
}

function _disable_field_after_build($form, &$form_state) {
  _form_disable_field($form['checkbox_field_name']);
  return $form;
}

function _form_disable_field(&$elements) {
  foreach (element_children($elements) as $key) {
    if (isset($elements[$key]) && $elements[$key]) {
      // Recurse through all children elements.
      _form_disable_field($elements[$key]);
    }
  }
  if (!isset($elements['#attributes'])) {
    $elements['#attributes'] = array();
  }
  $elements['#attributes']['disabled'] = 'disabled';
}

I found this thread after running into a similar problem when trying to use #default_value in form elements when using AJAX callbacks. Here is some example code for doing this:

/**
 * Example of how to set default values for form fields when using AJAX callbacks.
 * 
 * In this example, the form has a select field called "Size" and a text
 * field called "Price".  When the user selects a different value for
 * "Size", the value of "Price" is updated automatically via AJAX.
 */
function my_example_form($form, &$form_state) {
  $form['size'] = array(
    '#title' => t('Size'),
    '#type' => 'select',
    '#options' => array(
        0 => '--',
        1 => 'Small',
        2 => 'Medium',
        3 => 'Large'
     ),
    // #default_value only gets used the first time the form page is loaded,
    // NOT for any subsequent AJAX calls
    '#default_value' => 0,
    '#ajax' => array(
      'callback' => 'my_example_ajax_callback',
      'wrapper' => 'price-wrapper',
      'method' => 'replace',
      'effect' => 'fade',
    ),
  );
  $form['price'] = array(
    '#title' => t('Price'),
    '#type' => 'textfield',
    '#prefix' => '<div id="price-wrapper">',
    '#suffix' => '</div>',
  );
  $form['submit'] = array(
    '#type' => 'submit',
    '#value' => t('Submit'),
  );

  return $form;
}

function my_example_ajax_callback($form, &$form_state) {
  if (!empty($form_state['values']['size'])) {
    $size = $form_state['values']['size'];
    if ($size == 1) {
      // You could also do something like:
      // $form['price']['#value'] = $form['price']['#default_value']
      // if your form builder function already computed/set a #default_value
      $form['price']['#value'] = '$1.99';
    }
    if ($size == 2) {
      $form['price']['#value'] = '$2.99';
    }
    if ($size == 3) {
      $form['price']['#value'] = '$3.99';
    }
  }
  else {
    $form['price']['#value'] = '';
  }

  return $form['price'];
}

function my_example_form_submit($form, &$form_state) {
  $size = $form_state['values']['size'];
  $price = $form_state['values']['price'];
  drupal_set_message(t('You submitted: Size = %size, Price = %price', array('%size' => $size, '%price' => $price)));
}

Simplest solution is to use #value in ajax callback.

#default_value won't work