Magento 2：切换配送方式时如何在collect方法中获取正确配送金额

需求：开发基于配送金额向订单收取自定义费用的功能。
问题：切换配送方式时，fetch方法能获取正确的配送金额，但collect方法中获取的金额错误，如何获取选中配送方式的正确金额？

问题原因 #

在Magento的总额计算流程中，collect方法执行阶段，$quote->getShippingAddress()->getShippingAmount()可能尚未同步最新选中的配送方式金额。而collect方法的$shippingAssignment参数包含了当前活跃的配送信息，是实时更新的，应该从这里获取正确的配送金额。

修改方案 #

修改collect方法，从$shippingAssignment中提取当前选中的配送方式金额，替换原有的直接从shipping address获取的逻辑：

修改后的完整代码 #

<?php

namespace Nikunj\CustomFee\Model\Quote;

use Magento\Quote\Api\Data\ShippingAssignmentInterface as ShippingAssignmentInterfaceAlias;
use Magento\Quote\Model\Quote\Address\Total;

class Customfee extends \Magento\Quote\Model\Quote\Address\Total\AbstractTotal
{
    /**
     * Collect grand total address amount
     *
     * @param \Magento\Quote\Model\Quote $quote
     * @param ShippingAssignmentInterfaceAlias $shippingAssignment
     * @param Total $total
     * @return $this
     */
    protected $quoteValidator = null;

    public function __construct(\Magento\Quote\Model\QuoteValidator $quoteValidator)
    {
        $this->quoteValidator = $quoteValidator;
    }

    public function collect(
        \Magento\Quote\Model\Quote               $quote,
        ShippingAssignmentInterfaceAlias         $shippingAssignment,
        Total $total
    ) {
        parent::collect($quote, $shippingAssignment, $total);

        // 跳过无配送项的情况
        $shippingItems = $shippingAssignment->getItems();
        if (!count($shippingItems)) {
            return $this;
        }

        // 从shippingAssignment获取当前选中的配送金额
        $shippingAmount = $shippingAssignment->getShipping()->getAmount();
        $exist_amount = 0; //$quote->getCustomfee();
        $customfee = ($shippingAmount + 15);
        $balance = $customfee - $exist_amount;//final amount

        $total->setTotalAmount('customfee', $balance);
        $total->setBaseTotalAmount('customfee', $balance);

        $total->setCustomfee($balance);
        $total->setBaseCustomfee($balance);

        $total->setGrandTotal($total->getGrandTotal() + $balance);
        $total->setBaseGrandTotal($total->getBaseGrandTotal() + $balance);

        return $this;
    }

    protected function clearValues(Total $total)
    {
        $total->setTotalAmount('subtotal', 0);
        $total->setBaseTotalAmount('subtotal', 0);
        $total->setTotalAmount('tax', 0);
        $total->setBaseTotalAmount('tax', 0);
        $total->setTotalAmount('discount_tax_compensation', 0);
        $total->setBaseTotalAmount('discount_tax_compensation', 0);
        $total->setTotalAmount('shipping_discount_tax_compensation', 0);
        $total->setBaseTotalAmount('shipping_discount_tax_compensation', 0);
        $total->setSubtotalInclTax(0);
        $total->setBaseSubtotalInclTax(0);
    }

    /**
     * Assign subtotal amount and label to address object
     *
     * @param \Magento\Quote\Model\Quote $quote
     * @param Total $total
     * @return array
     */
    public function fetch(\Magento\Quote\Model\Quote $quote, Total $total)
    {
        $fee = ($quote->getShippingAddress()->getShippingAmount()+15);
        return [
            'code' => 'customfee',
            'title' => 'Custom Fee',
            'value' => $fee
        ];
    }

    /**
     * Get Subtotal label
     *
     * @return \Magento\Framework\Phrase
     */
    public function getLabel()
    {
        return __('Custom Fee');
    }
}

关键修改点 #

1. 添加无配送项判断：避免在未选择配送方式时出现计算错误。
2. 从shippingAssignment获取配送金额：通过$shippingAssignment->getShipping()->getAmount()获取当前选中配送方式的实时金额，确保切换配送方式时金额同步更新。

内容的提问来源于stack exchange，提问作者Nikunj Rawat