how to get an uploaded file path in moodle - php

Question

I created a new activity and i uploaded a file correctly within it but when i used
$url = moodle_url::make_pluginfile_url($file->contextid, $file->component, $file->filearea, $file->itemid,$file->filepath, $file->filename);
to get the link the result is : Sorry, the requested file could not be found
I searched an I find that I have to add a pluginfile function in my lib and this is my function :
function testnew_pluginfile($course, $cm, $context, $component, $filearea, $itemid, $path, $filename) {
global $CFG, $DB;
require_course_login($course, true, $cm);
$fullpath = "/{$context->id}/$component/$filearea/$itemid/$path/$filename";
$fs = get_file_storage();
if (!$file = $fs->get_file_by_hash(sha1($fullpath))) {
return false;
}
send_stored_file($file, 0, 0, false);
}

Answer 1

The problem is the context id didn't came true. so I added my add_instance function to add a new context id in mdl_files table. This is my function:
function testnew_add_instance($data){
global $DB;
$cmid = $data->coursemodule;
$data->timemodified =time();
$data->id = $DB->insert_record('testnew', $data);
$DB->set_field('course_modules', 'instance', $data->id, array('id'=>$cmid));
$fs = get_file_storage();
$draftitemid = $data->type;
$context = context_module::instance($cmid);
file_save_draft_area_files($draftitemid, $context->id, 'mod_testnew', 'content', 0);
$files = $fs->get_area_files($context->id, 'mod_testnew', 'content', 0, 'sortorder', false);
if (count($files) == 1) {
// only one file attached, set it as main file automatically
$file = reset($files);
file_set_sortorder($context->id, 'mod_testnew', 'content', 0, $file->get_filepath(), $file->get_filename(), 1);
}
return $data->id;
}