Figuring this out took a while, as recorded at http://drupalbin.com/17844 for the onlookers and assisters in IRC.
Functions and API docs read over in the process included theme_field(), hook_preprocess_HOOK(), and template_preprocess_field().
Fail, fail, fail. The code runs, the print statements print, but rendered value of the field changes not one whit.
<?php
function dgd7glue_preprocess_field(&$vars) {
if ($vars['element']['#field_name'] == 'field_number') {
$vars['element']['#items'][0]['safe_value'] = 'New value';
$vars['element']['#items'][0]['value'] = 'Newer value';
print '<pre>';
print_r($vars['element']['#items'][0]['safe_value']);
print '</pre>';
print '<pre>';
print_r($vars['element']['#items'][0]['value']);
print '</pre>';
}
}
?>Getting smarter about the debug function (needs devel module enabled), and also finding what finally works:
<?php
// only the last one, $vars['items'][0]['#markup'], does anything.
function dgd7glue_process_field(&$vars) {
if ($vars['element']['#field_name'] == 'field_number') {
krumo($vars);
$vars['classes_array'] = array('so-the-damn-classes-work');
$vars['element']['label_hidden'] = FALSE;
$vars['element']['#items'][0]['safe_value'] .= ' New value';
$vars['element']['#items'][0]['value'] .= ' Newer value';
$vars['element'][0]['#markup'] .= ' Newest value';
$vars['items'][0]['#markup'] .= ' Newester value';
print '<pre>';
print_r($vars['element']['#items'][0]['safe_value']);
print '</pre>';
print '<pre>';
print_r($vars['element']['#items'][0]['value']);
print '</pre>';
print '<pre>';
print_r($vars['element'][0]['#markup']);
print '</pre>';
print '<pre>';
print_r($vars['items'][0]['#markup']);
print '</pre>';
}
}
?>