Drupal 7 Custom Field Widget not saving user input - drupal

Question

I'm building a custom field module to work with our streaming video provider. As part of this, I need to grab a video based on a selected category from the provider's API. The field will need to store a number of pieces - the selected category, the selected video, and some additional details (such as a caption) yet to be added.
I can get this form to appear on the node edit page (after attaching the field to a content type), but it doesn't appear to be saving the user's input. Here's the form in place on the edit node screen: Field on node editing screen. Workflow for the user is they select a category, which populates the list of videos to select. When they select a video, they're shown a preview in $element['teacherstv']['teacherstv_video_details']. This is working right up to the point where the user saves the form. At that point, the selected values are lost.
I've looked through the Field API and Forms API docs for D7, but can't see any clear instructions for how to set up this kind of field widget and have it save user input.
Here's the code for hook_field_widget_form()
function teacherstv_field_widget_form(&$form, &$form_state, $field, $instance, $langcode, $items, $delta, $element) {
// $value = $isset($items[$delta['teacherstv']) ? $items[$delta]['teacherstv'] : '';
$widget['#delta'] = $delta;
//lets get an array of our categories from core
$coreapi = new coreapi();
$APIsettings = variable_get('teacherstv_API_settings');
$coreapi->apiuser = $APIsettings['username'];
$coreapi->apipwd = $APIsettings['password'];
$coreapi->apiurl = $APIsettings['api_url'];
$coreapi->sortcriteria = "alpha";
//$categoriesavailable = $coreapi->get_categories();
$categories = coreapi_get_categories();
$defaults = $field['settings'];
$settings = $instance['settings'];
$category = !is_null($form_state['values'][$field['field_name']]['und'][$delta]['teacherstv']['teacherstv_category']) ? $form_state['values'][$field['field_name']]['und'][$delta]['teacherstv']['teacherstv_category'] : $defaults['teacherstv']['defaultcategory'];
switch ($instance['widget']['type']) {
case 'teacherstv':
$element['teacherstv'] = array(
'#tree' => TRUE,
'#type' => 'fieldset',
'#title' => t('TeachersTV Video'),
'#description' => '<p>' . t('Select a video from the TeachersTV service to embed.') . '</p>',
'#delta' => $delta,
);
$element['teacherstv']['teacherstv_category'] = array(
'#type' => 'select',
'#field_parents' => 'teacherstv',
'#title' => t('Video Categories'),
'#options' => $categories,
'#description' => t('Select a video category for a list of videos'),
'#default_value' => !is_null($settings['teacherstv_category']) ? array($settings['teacherstv_category']) : array($category),
'#ajax' => array(
'callback' => 'teacherstv_ajax_videolist',
'wrapper' => 'teacherstv-videolist-' . $delta . '-div',
'method' => 'replace',
),
'#delta' => $delta,
);
$videos = coreapi_list_videos($category);
$videos[0] = "--Please select a video--";
asort($videos);
$element['teacherstv']['teacherstv_video'] = array(
'#type' => 'select',
'#title' => t('Select a video'),
'#field_parents' => 'teacherstv',
'#prefix' => '<div id="teacherstv-videolist-' . $delta . '-div">',
'#suffix' => '</div>',
'#options' => array(0 => 'Video 1'),
'#default_value' =>
isset($form_state['values'][$field['field_name']]['und'][$delta]['teacherstv']['teacherstv_video']) ? $form_state['values'][$field['field_name']]['und'][$delta]['teacherstv']['teacherstv_video'] : NULL,
'#description' => t('Select a video.'),
'#options' => $videos,
'#ajax' => array(
'callback' => 'teacherstv_ajax_videoselect',
'wrapper' => 'teacherstv-videodetails-' . $delta . '-div',
),
'#delta' => $delta,
);
$video_keys = array_keys($videos);
$selected_video = isset($form_state['values'][$field['field_name']]['und'][$delta]['teacherstv_category']) ? $form_state['values'][$field['field_name']]['und'][$delta]['teacherstv_category'] : NULL;
$element['teacherstv']['teacherstv_video_details'] = array(
'#type' => 'markup',
'#field_parents' => 'teacherstv',
'#title' => t('Video details'),
'#prefix' => '<div id="teacherstv-videodetails-' . $delta . '-div">',
'#suffix' => '</div>',
'#description' => t('Details about the video.'),
'#markup' => teacherstv_ajax_render_video($selected_video),
'#delta' => $delta,
);
break;
}
return $element;
}

Answer 1

Its probably the AJAX callback , in your AJAX callback, use
$form_state['rebuild'] = TRUE;
or assign the ajax value to a new element to have it in the $form_state array..
use devel and dpm($form_state). I bet your value is ""