Moodle: Error on form submission in activity module - php

Question

Below is a sample of the code that I'm using for the form and then the handling og the file saving. There's something that I'm doing wrong, but I'm not sure what it is. Please assist. I have attached a screenshot showing the error that I'm getting after submitting the form.
error on form submission in moodle inside activity module
class mod_audio_mod_form extends moodleform_mod {
/**
* Defines forms elements
*/
public function definition() {
global $CFG;
$mform = $this->_form;
// Adding the "general" fieldset, where all the common settings are showed.
$mform->addElement('header', 'general', get_string('general', 'form'));
// Adding the standard "name" field.
$mform->addElement('text', 'name', get_string('audioname', 'audio'), array('size' => '64'));
if (!empty($CFG->formatstringstriptags)) {
$mform->setType('name', PARAM_TEXT);
} else {
$mform->setType('name', PARAM_CLEANHTML);
}
$mform->addRule('name', null, 'required', null, 'client');
$mform->addRule('name', get_string('maximumchars', '', 255), 'maxlength', 255, 'client');
$mform->addHelpButton('name', 'audioname', 'audio');
// Adding the standard "intro" and "introformat" fields.
if ($CFG->branch >= 29) {
$this->standard_intro_elements();
} else {
$this->add_intro_editor();
}
// Adding the rest of audio settings, spreading all them into this fieldset
// ... or adding more fieldsets ('header' elements) if needed for better logic.
$mform->addElement('header', 'audiofieldset', get_string('audiofieldset', 'audio'));
$filemanager_options = array();
$filemanager_options['accepted_types'] = '*';
$filemanager_options['maxbytes'] = 0;
$filemanager_options['maxfiles'] = -1;
$filemanager_options['mainfile'] = true;
$mform->addElement('filemanager', 'files', get_string('selectfiles'), null, $filemanager_options);
$mform->addRule('files', null, 'required', null, 'client');
// Add standard grading elements.
$this->standard_grading_coursemodule_elements();
// Add standard elements, common to all modules.
$this->standard_coursemodule_elements();
// Add standard buttons, common to all modules.
$this->add_action_buttons();
}
function data_preprocessing(&$default_values) {
if ($this->current->instance) {
// editing existing instance - copy existing files into draft area
$draftitemid = file_get_submitted_draft_itemid('files');
file_prepare_draft_area($draftitemid, $this->context->id, 'mod_audio', 'content', 0, array('subdirs' => true));
$default_values['files'] = $draftitemid;
}
}
function definition_after_data() {
if ($this->current->instance and $this->current->tobemigrated) {
// resource not migrated yet
return;
}
parent::definition_after_data();
}
function validation($data, $files) {
global $USER;
$errors = parent::validation($data, $files);
$usercontext = context_user::instance($USER->id);
$fs = get_file_storage();
if (!$files = $fs->get_area_files($usercontext->id, 'user', 'draft', $data['files'], 'sortorder, id', false)) {
$errors['files'] = get_string('required');
return $errors;
}
if (count($files) == 1) {
// no need to select main file if only one picked
return $errors;
} else if (count($files) > 1) {
$mainfile = false;
foreach ($files as $file) {
if ($file->get_sortorder() == 1) {
$mainfile = true;
break;
}
}
// set a default main file
if (!$mainfile) {
$file = reset($files);
file_set_sortorder($file->get_contextid(), $file->get_component(), $file->get_filearea(), $file->get_itemid(), $file->get_filepath(), $file->get_filename(), 1);
}
}
return $errors;
}
}
// THE CLASS IN LOCALLIB.PHP
class audio_content_file_info extends file_info_stored {
public function get_parent() {
if ($this->lf->get_filepath() === '/' and $this->lf->get_filename() === '.') {
return $this->browser->get_file_info($this->context);
}
return parent::get_parent();
}
public function get_visible_name() {
if ($this->lf->get_filepath() === '/' and $this->lf->get_filename() === '.') {
return $this->topvisiblename;
}
return parent::get_visible_name();
}
function save_files($data) {
global $DB;
// Storage of files from the filemanager (videos).
$draftitemid = $data->files;
if ($draftitemid) {
file_save_draft_area_files(
$draftitemid, $this->context->id, 'mod_audio', 'files', 0
);
}
}
}
// FUNCTION THAT ADDS THE INSTANCE IN LIB.PHP
function audio_add_instance(stdClass $audio, mod_audio_mod_form $mform = null) {
global $CFG, $DB;
require_once("$CFG->libdir/resourcelib.php");
require_once("$CFG->dirroot/mod/audio/locallib.php");
$cmid = $audio->coursemodule;
$audio->timecreated = time();
$audio->timemodified = time();
resource_set_display_options($audio);
$audio->id = $DB->insert_record('audio', $audio);
$context = context_module::instance($audio->coursemodule);
$audiofile = new audio_content_file_info($context, null, null);
$audiofile->save_files($audio);
// we need to use context now, so we need to make sure all needed info is already in db
$DB->set_field('course_modules', 'instance', $audio->id, array('id' => $cmid));
resource_set_mainfile($audio);
return $audio->id;
}
Please advice on what I could be doing wrong here.