Backend\Core\Engine\Form::addFile PHP Method

    public function addFile($name, $class = null, $classError = null)
    {
        $name = (string) $name;
        $class = $class !== null ? (string) $class : 'fork-form-file';
        $classError = $classError !== null ? (string) $classError : 'error';
        // add element
        $this->add(new FormFile($name, $class, $classError));
        return $this->getField($name);
    }

 public function loadForm()
 {
     $this->form = new Form('settings');
     // we don't even have a auth config file yet, let the user upload it
     if ($this->get('fork.settings')->get($this->getModule(), 'certificate') === null) {
         $this->form->addFile('certificate');
         $this->form->addtext('email');
         return;
     }
     // we are authenticated! Let's see which account the user wants to use
     if ($this->get('fork.settings')->get($this->getModule(), 'account') === null) {
         $analytics = $this->get('analytics.google_analytics_service');
         try {
             $accounts = $analytics->management_accounts->listManagementAccounts();
         } catch (Google_Service_Exception $e) {
             $this->tpl->assign('email', $this->get('fork.settings')->get($this->getModule(), 'email'));
             return $this->tpl->assign('noAccounts', true);
         }
         $accountsForDropdown = array();
         foreach ($accounts->getItems() as $account) {
             $accountsForDropdown[$account->getId()] = $account->getName();
         }
         $this->form->addDropdown('account', $accountsForDropdown);
         return;
     }
     // we have an account, but don't know which property to track
     if ($this->get('fork.settings')->get($this->getModule(), 'web_property_id') === null) {
         $analytics = $this->get('analytics.google_analytics_service');
         $properties = $analytics->management_webproperties->listManagementWebproperties($this->get('fork.settings')->get($this->getModule(), 'account'));
         $propertiesForDropdown = array();
         foreach ($properties->getItems() as $property) {
             $propertiesForDropdown[$property->getId()] = $property->getName();
         }
         $this->form->addDropdown('web_property_id', $propertiesForDropdown);
         return;
     }
     // we have an account, but don't know which property to track
     if ($this->get('fork.settings')->get($this->getModule(), 'profile') === null) {
         $analytics = $this->get('analytics.google_analytics_service');
         $profiles = $analytics->management_profiles->listManagementProfiles($this->get('fork.settings')->get($this->getModule(), 'account'), $this->get('fork.settings')->get($this->getModule(), 'web_property_id'));
         $profilesForDropdown = array();
         foreach ($profiles->getItems() as $property) {
             $profilesForDropdown[$property->getId()] = $property->getName();
         }
         $this->form->addDropdown('profile', $profilesForDropdown);
         return;
     }
 }