取消按钮在Moodle中提交表单数据

Initially I don't use the cancel button in my moodle form. My form looks like:

require_once("{$CFG->libdir}/formslib.php");

class quest_form extends moodleform {

    function definition() {
        global $DB;
        $mform =&$this->_form;

        $mform->addElement('header','displayinfo', 'Add Question');

        // add question.
        $mform->addElement('editor', 'title', 'Question');
        $mform->addRule('title', null, 'required', null, 'client');
        $mform->setType('title', PARAM_RAW);
        // add answer.
        $mform->addElement('editor', 'answer', 'Answer');
        $mform->addRule('answer', null, 'required', null, 'client');
        $mform->setType('answer', PARAM_RAW);

        $mform->addElement('hidden', 'blockid');
        $mform->setType('blockid', PARAM_RAW);
        $mform->addElement('hidden', 'courseid');
        $mform->setType('courseid', PARAM_RAW);
        $this->add_action_buttons(false, 'submit');
    }

Now I want to use cancel button in my form so I replace the line

$this->add_action_buttons(false, 'submit');

with

$this->add_action_buttons(true, 'submit');

The cancel button is displayed successfully but while clicking the cancel button the form gets submitted(even if there is no data in form fields).

How can I resolve this? Am I miss anything else??

Please help me...

EDIT

Depending upon Russell England answer. I try like below:

    $qform = new quest_form ();
    if ($qform ->is_cancelled()){
      redirect("view.php?id={$cid}");
    }else{
      $qform = new pool_form("pool_action.php?id={$cid}&qpid={$questplace->id}&qtype={$qtype}");
    }   
    $qform ->display();

But still the cancel button submit the form.

You need to check if the form has been cancelled in the calling php file. eg:

$form = new quest_form();

if ($form->is_cancelled()) {
    // Display a message or redirect somewhere.
    redirect(new moodle_url('/foldername/cancelquesturl.php'));
} else if ($data = $form->get_data()) {
    // Do something with the data.
}