How to fill form fields based on other fields values using AJAX

Question

I have 3 fields. On blur on any of them I want to look for empty ones - if blurred one has value and any of the others does not, I want to copy value.

Obtaining value is easy, simply $form_state['triggering_element']['#value'], but setting it elsewhere gets tricky.

Changing $form['item']['#default_value'] does not work if field is empty after user's edit. Changing $form['item']['#value'] makes Drupal ignore any further user input. Changing $form_state['values'] seems to do nothing. What is the correct approach that should work? When I'll know that, I'll be able to debug.

Answer 1

I had the same issue and this workaround did the trick. Basically you clear up $form_state['input'] value and rebuild the form.

Form builder:

<?php 
$form['test'] = array(
  '#type' => 'textfield', 
  '#title' => t('Test'),
  '#ajax' => array(
    'callback' => 'my_test_callback_func',
    'wrapper' => 'edit-test2',
    'progress' => array(
      'message' => '',
      'type' => 'throbber',
    ),
  ),
);

$form['test2'] = array(
  '#type' => 'textfield', 
  '#prefix' => '<div id="edit-test2">',
  '#suffix' => '</div>', 
  '#title' => t('Test2'),
);
?>

Ajax callback function: This is the trickier part.

<?php 
function my_test_callback_func($form, &$form_state) {
  unset($form_state['input']['test2'], $form_state['values']['test2']);
  $form['test2']['#default_value'] = 'Auto Filled!';
  $form_state['input']['test2'] = 'Auto Filled!';
  return form_builder($form['#id'], $form['test2'], $form_state);
}
?>

We unset the user input (or check if it's empty), set a default value and then rebuild the form.

Answer 2

The solution was, as Clive suggested, to simply use:

$form_state['input']['item'] = '...';

For elements that got replaced by AJAX, works like a charm.

If that's not enough, using AJAX commands might be needed.