Drupal 7 Module Development

Creating New Fields
Formatters follow a very similar pattern to field types and widgets. There is an
info hook to define what formatters are available, and then there's a series of
callbacks for all of the formatters our module defines. In most cases though,
there's only one callback we need worry about.
Declaring a formatter
First, let's look at the info hook given here:
function dimfield_field_formatter_info() {
return array(
'dimfield_default' => array(
'label' => t('Default'),
'field types' => array('dimensions'),
),
'dimfield_table' => array(
'label' => t('Show as table'),
'field types' => array('dimensions'),
'settings’ => array('units_as' => 'column'),
),
);
}
In the preceding snippet we define two formatters, and there's not much to define.
Each formatter has an internal name defined by the array key, a human-readable
label, and a list of the field types that it applies to. Just as with widgets, we can define
a formatter in any module that works with any field type we want, as long as we
know how to handle the data it gives us.
Single-value formatters
Formatters only have two callbacks, and most formatters will only use one. Again,
let's look at the simple implementation first.
function dimfield_field_formatter_view($obj_type, $object, $field,
$instance, $langcode, $items,
$display) {
$element = array();
$settings = $display['settings'];
switch ($display['type']) {
case 'dimfield_default':
foreach ($items as $delta => $item) {
if ($field['settings']['num_dimensions'] == 2) {
$output = t('@height @unit by @width @unit', array(
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