[Solved] Custom Field doesn't save data

I should mention I get this error when viewing the saved page.

Notice: Undefined index: latlng in fieldTesting_field_formatter_view() (line 157 of C:\wamp\www\d7a7\sites\all\modules\fieldTesting\fieldTesting.module).
Notice: Undefined index: latlng in fieldTesting_field_formatter_view() (line 161 of C:\wamp\www\d7a7\sites\all\modules\fieldTesting\fieldTesting.module).

And if I fix it by removing ['latlng'] from those lines, it breaks the preview. And the saved page still won't show the data.

For anyone who is searching for the answer to the same problem, here's what I learned.

Don't treat the field columns you created as a subarray to the field. I was thinking of ['latitude'] and ['longitude'] being under ['latlng']. When I should have thought of them as just ['latitude'] and ['longitude'].

In your widget form, say something like $element['lat'] = array(); $element['lng'] = array();
Don't do: $element['latlng'] = array(); $element['latlng']['lat'] = array(); etc...

Here's my working code for reference.

// $Id$
/**
* fieldTesting module file.
* @file
*/

/**
* implementation of hook_help().
*/
function fieldTesting_help($path, $arg)
{
	if ($path == 'admin/help#fieldTesting')
	{
		$txt = 'Useless module to learn how to use fields.';
		$replace = array();
		return '<p>'. t($txt, $replace) .'</p>';
	}
}//end _help()

/**
 * Implementation of hook_menu
 */
function fieldTesting_menu() {
  $items = array();
  $items['fieldTesting'] = array(
    'title' => 'fieldTesting',
    'description' => 'fieldTesting Page.',
    'page callback' => 'fieldTesting_page',
  );  
  return $items;
}

function filedTesting_page()
{
    $output = "This is the field testing page. Nothing is here.";
    return $output;
}
/**
 * Implements hook_permission().
 */
function fieldTesting_permission() {
  return array(
    'administer fieldTesting' => array(
      'title' => t('administer fieldTesting'),
      'description' => t('Administer fieldTesting module'),
    ),
  );
}

/**
 * Implements hook_field_info().
 *
 * Provides the description of the field.
 */
function fieldTesting_field_info() {
  return array(
    'field_latlng' => array(
      'label' => t('Latitude and Longitude'),
      'description' => t('Store the decimal value of a latitude and longitude pair'),
      'default_widget' => 'latlng_text',
      'default_formatter' => 'latlng_simple_text',
    ),
  );
}

/**
 * Implements hook_field_schema().
 */
function fieldTesting_field_schema($field)
{
    $columns = array(
        'lat_value' => array(
            'type' => 'float',
        ),
        'lng_value' => array(
            'type' => 'float',
        ),
    );
    return array('columns' => $columns);
}

/**
 * Implements hook_field_validate().
 */
function fieldTesting_field_validate($obj_type, $object, $field, $instance, $langcode, &$items, &$errors)
{
    $regexFloatInt = '/^[-+]?([0-9]+(\.[0-9]+)?|\.[0-9]+)$/';
    foreach($items as $delta => $item)
    {
        //$errors[$field['field_name']][$langcode][$delta][] = array();
        if(isset($item['lat_value']) && isset($item['lng_value']))
        {
            if($item['lat_value']=='' || $item['lng_value']=='')
            {
                $errors[$field['field_name']][$langcode][$delta][] = array(
                        'error' => 'latlng_invalid',
                        'message' => t('Latitude and Longitude must be entered as a pair, make sure you have a value in both boxes.'),
                    );
            }
            if(!preg_match($regexFloatInt, $item['lat_value']) || !preg_match($regexFloatInt, $item['lng_value']))
            {
                $errors[$field['field_name']][$langcode][$delta][] = array(
                    'error' => 'latlng_invalid',
                    'message' => t('Latitude\'s and Longitudes must be float or integer values.'),
                );
            }
            else if($item['lat_value']>=90 || $item['lat_value']<=(-90) || $item['lng_value']>=180 || $item['lng_value']<=(-180))
            {
                $errors[$field['field_name']][$langcode][$delta][] = array(
                    'error' => 'latlng_invalid',
                    'message' => t('Latitude\'s must be between -90 and 90. Longitude\'s must be between -180 and 180.'),
                );
            }
        }
        
    }
}

/**
 * Implements hook_field_is_empty().
 */
function fieldTesting_field_is_empty($item, $field)
{
    if(empty($item['lng_value']))
        return true;
    if(empty($item['lat_value']))
        return true;
    else
        return false;
}

/**
 * Implements hook_field_formatter_info().
 */
function fieldTesting_field_formatter_info()
{
    return array(
        // This formatter just displays the hex value in the color indicated.
        'latlng_simple_text' => array(
            'label' => t('Textbox to enter latitudes and longitudes'),
            'field types' => array('field_latlng'),
        ),
    );
}

/**
 * Implements hook_field_formatter_view().
 */
function fieldTesting_field_formatter_view($entity_type, $entity, $field, $instance, $langcode, $items, $display)
{
    //var_dump($items);
  $element = array();

  switch ($display['type']) {
    // This formatter simply outputs the field as text and with a color.
    case 'latlng_simple_text':        
      foreach ($items as $delta => $item) {
        $element[$delta]['#markup'] ='';
        if($item['lat_value'])
        {
            $element[$delta]['#markup'] .= '<p>' . t('The latitude is @code', array('@code' => $item['lat_value'])) . '</p>';
        }
        if($item['lng_value'])
        {
            $element[$delta]['#markup'] .= '<p>' . t('The longitude is @code', array('@code' => $item['lng_value'])) . '</p>';
        }
      }
      break;
  }
  return $element;
}

/**
 * Implements hook_field_widget_info().
 */
function fieldTesting_field_widget_info()
{
  return array(
    'latlng__simple_text' => array(
      'label' => t('Latitude and Longitude Textbox'),
      'field types' => array('field_latlng'),
    ),
  );
}

/**
 * Implements hook_field_widget_form().
 */
function fieldTesting_field_widget_form(&$form, &$form_state, $field, $instance, $langcode, $items, $delta, $element)
{
    drupal_set_message('fieldTesting field widget form called.');
       
    $latValue = isset($items[$delta]['lat_value']) ? $items[$delta]['lat_value'] : 'error';
    $lngValue = isset($items[$delta]['lng_value']) ? $items[$delta]['lng_value'] : 'error';
  $element += array(
    '#delta' => $delta,
  );
  $element['lat_value'] = array();
  $element['lng_value'] = array();
  switch ($instance['widget']['type'])
  {
    case 'latlng__simple_text':
          $element['lat_value'] = array(
              '#title' => t('Latitude'),
            '#type' => 'textfield',
            '#default_value' => $latValue,
            '#size' => 20,
            '#maxlength' => 20,
            );
          $element['lng_value'] = array(
              '#title' => t('Longitude'),
            '#type' => 'textfield',
            '#default_value' => $lngValue,
            '#size' => 20,
            '#maxlength' => 20,
            );
      break;
      default:
          break;
  }
  return $element;
}

/**
 * Implements hook_field_widget_error().
 */
function fieldTesting_field_widget_error($element, $error, $form, &$form_state) {
  switch ($error['error']) {
    case 'latlng_invalid':
      form_error($element, $error['message']);
      break;
  }
}