/**
     * Returns the currently requested sort information.
     * @param bool $recalculate whether to recalculate the sort directions
     * @return array sort directions indexed by attribute names.
     * Sort direction can be either `SORT_ASC` for ascending order or
     * `SORT_DESC` for descending order.
     */
    public function getAttributeOrders($recalculate = false)
    {
        if ($this->_attributeOrders === null || $recalculate) {
            $this->_attributeOrders = [];
            if (($params = $this->params) === null) {
                $request = Yii::$app->getRequest();
                $params = $request instanceof Request ? $request->getQueryParams() : [];
            }

            //反馈：这里当存在排序参数并且排序参数为空时，也会执行下面的代码，从而导致无法执行最后的默认排序，
           //当我想继承这个Sort类，对这部分代码进行部分修改时，private _attributeOrders 属性又限制对这个方法的部分代码修改，
           //建议：将 isset($params[$this->sortParam]) 改为 isset($params[$this->sortParam])&&empty(isset($params[$this->sortParam])) 或者其他
            if (isset($params[$this->sortParam])) {
                foreach ($this->parseSortParam($params[$this->sortParam]) as $attribute) {
                    $descending = false;
                    if (strncmp($attribute, '-', 1) === 0) {
                        $descending = true;
                        $attribute = substr($attribute, 1);
                    }

                    if (isset($this->attributes[$attribute])) {
                        $this->_attributeOrders[$attribute] = $descending ? SORT_DESC : SORT_ASC;
                        if (!$this->enableMultiSort) {
                            return $this->_attributeOrders;
                        }
                    }
                }

                return $this->_attributeOrders;
            }
            if (empty($this->_attributeOrders) && is_array($this->defaultOrder)) {
                $this->_attributeOrders = $this->defaultOrder;
            }
        }

        return $this->_attributeOrders;
    }