Prado\Web\UI\TControl::setViewState PHP Method

    public function setViewState($key, $value, $defaultValue = null)
    {
        if ($this->_trackViewState) {
            unset($this->_tempState[$key]);
            $this->_viewState[$key] = $value;
        } else {
            unset($this->_viewState[$key]);
            if ($value === $defaultValue) {
                unset($this->_tempState[$key]);
            } else {
                $this->_tempState[$key] = $value;
            }
        }
    }