Yii file CFormInputElement won't display unless explicitly marked "safe" - file-upload

Question

I'm trying to use Form Builder to build a simple file upload prompt. I want to specify the rule for the file to be similar to
array('formFile', 'file', 'allowEmpty' => false, 'types' => 'html'),
but something is wrong. The file upload element only appears if I explicitly mark the element as 'safe' (and remove the 'file' rule). What am I missing?
models/UploadForm.php
class UploadForm extends CFormModel
{
public $year;
public $formFile;
public function rules ()
{
return array(
array('year', 'required'),
array('year', 'date', 'format'=>'yyyy'),
// array('formFile', 'safe'),
array('formFile', 'file', 'allowEmpty' => false, 'types' => 'html'),
);
}
static public function getYearOptions () {...}
}
views/extranet/uploadForm.php
return array(
'title' => 'Select year',
'method' => 'post',
'enctype' => 'multipart/form-data',
'elements' => array(
'year' => array(
'type' => 'dropdownlist',
'items' => UploadForm::getYearOptions(),
),
'formFile' => array(
'type' => 'file',
'label' => 'form source file',
),
),
'buttons' => array(
'upload' => array(
'type' => 'submit',
'label' => 'upload',
),
),
);
controllers/ExtranetController.php
class ExtranetController extends CController
{
public function actionIndex ()
{
$form = new CForm('application.views.extranet.uploadForm', new UploadForm());
if ($form->submitted('upload') && $form->validate()) {...}
$this->render('index', array('form' => $form));
}
}

Answer 1

The reason for this is very simple.
The form builder only renders input elements which are considered safe (I.E. have a validation rule). What you have done is perfectly fine, except CFileValidator isn't "safe" by default, whereas other validators are safe.
The quickest way to solve this is the following:
// In your model::rules() function
return array(
array('formFile', 'file', 'allowEmpty' => false, 'types' => 'html', 'safe' => true),
);
Refer to these two links for more information: the CFileValidator#safe documentation, and the Github issue for a problem very similar to yours.