Filter::getFields

public function getFields()
{
	if($this->fields === null)
	{
		$this->fields = $this->entityDataProvider->prepareFields();
		foreach($this->extraProviders as $dataProvider)
		{
			$fields = $dataProvider->prepareFields();
			if(!empty($fields))
			{
				$this->fields += $fields;
			}
		}
	}
	return $this->fields;
}