Form doesn't validate after submitting in moodle - php

Question

I am trying to create a form whose structure depends on the parameter in the url. If no parameter is specified in the url, an error message should be displayed. Depending on the id, a database query is performed and the form is filled with data.
example url: http://127.0.0.1/local/group/signin.php?groupid=14
Unfortunately, my form doesn't validate after I submit the form via pressing the action button. It jumps to http://127.0.0.1/local/group/signin.php and because there is no parameter present in the url the error message 'No group found' is displayed.
What have I done wrong here?
signinform.php:
class signinform extends moodleform {
public function definition() {
global $DB;
global $USER;
$mform = $this->_form;
$urlid = $this->_customdata['id']; // get the passed group id
$message = 'No group found';
if(is_null($urlid)){
$mform->addElement('html', '<h3>'.\core\notification::error($message).'</h3>');
}
else{
// build the form, sql query etc.
$this->add_action_buttons(true, 'Submit');
}
}
function validation($data, $files) {
return array();
}
}
signin.php:
$PAGE->set_url(new moodle_url('/local/schedule/signin.php?'));
$PAGE->set_context(\context_system::instance());
$PAGE->set_pagelayout('base');
$PAGE->set_title("Sign up");
$PAGE->set_heading("Sign up for a group");
global $DB;
global $USER;
$urlid = $_GET["id"];
$to_form = array('id' => $urlid); // pass group id to form
$mform = new signinform(null, $to_form);
$homeurl = new moodle_url('/');
if ($mform->is_cancelled()) {
redirect($homeurl, 'Cancelled.'); // Just for testing, never enters here
} else if ($fromform = $mform->get_data()) {
redirect($homeurl, 'Validation in process'); // Just for testing, never enters here
}
echo $OUTPUT->header();
$mform->display();
echo $OUTPUT->footer();

Answer 1

You need to add a hidden field to the form that contains the 'id' that has to be passed to the page, otherwise, when the form is submitted, that id will no longer be present in the params for that page.
e.g. (in definition())
$mform->addElement('hidden', 'id', $urlid);
$mform->setType('id', PARAM_INT);
Also, in Moodle, you should never access $_GET directly - use the wrapper functions required_param() or optional_param(), as these:
Clean the parameter to the declared type
Automatically take parameters from either $_GET or $_POST (which will be important in this case, as the 'id' param will be part of the POST data, when you submit the form)
Handle missing parameters by either applying a default (optional_param) or stopping with an error message (required_param)
So your access to $_GET['id'], should be replaced with:
$urlid = optional_param('id', null, PARAM_INT);