kartik\export\ExportMenu::initSelectedColumns PHP Method

    protected function initSelectedColumns()
    {
        if (!$this->_columnSelectorEnabled) {
            return;
        }
        $this->selectedColumns = array_keys($this->columnSelector);
        if (!isset($_POST[self::PARAM_EXPORT_COLS]) or !strlen($_POST[self::PARAM_EXPORT_COLS])) {
            return;
        }
        $this->selectedColumns = Json::decode($_POST[self::PARAM_EXPORT_COLS]);
    }