How to intercept the loading of a field?

Question

I have a field called field_price. How do I get that field on my page to display Free when the value is $0.00, and the actual value every other time?

I tried to intercept the loading of the field by doing things like:

mytemplate_hook_load(){
// do stuff
}

mytemplate_process_field(){
// do stuff
}

mytemplate_preprocess_field(){
// do stuff
}

etc.. etc.. etc..

I tried so many different permutations of the above as modules, template, changing function names etc... But none of them ever fire. I know I have the Field module enabled.

What am I doing wrong?

Note: I am using drupal 7

Answer 1

Ok, i figured it out. I put this code into my template.php of my theme:

function johncustom_field__field_price(&$variables) {
        if($variables['element'][0] == '$0.00') return 'Free';
        else return $variables['element'][0];
}

I also had to clear the cache several times before this function would fire.

Answer 2

I believe hook_field_formatter_view is the answer for your question. It says

Build a renderable array for a field value.

Using above hook in a custom module you can change the field value !

For Example, if your custom module name is johncustom then your function inside module file should be

function johncustom_field_formatter_view($entity_type, $entity, $field, $instance, $langcode, $items, $display) {
  $element = array();
  // Change display type & Check for your field here
  switch ($display['type']) {
    // Override check plain
    case 'taxonomy_term_reference_plain':
      foreach ($items as $delta => $item) {
        $element[$delta] = array(
          '#markup' => mymodule_crazy_fun_plain($item['value']),
        );
      }
    break;
  }
  return $element;
}