public function getHeaderPrototype()
{
if ($this->headerPrototype === NULL) {
$this->headerPrototype = \Nette\Utils\Html::el('th')->setClass(['column', 'grid-header-' . $this->getName()]);
}
if ($this->isSortable() && $this->getSort()) {
$this->headerPrototype->class[] = $this->getSort() == self::ORDER_DESC ? 'desc' : 'asc';
}
return $this->headerPrototype;
}