Magento2 添加动态自定义费用magento 2

我正在为magento 2构建一个自定义费用模块。我在结帐页面中添加了一个复选框，如果用户勾选了该复选框，我将向订单中添加自定义费用。在本教程之后，我成功地将自定义费用添加到订单中：

然而，我的自定义费用是动态的，因为它是从外部API获取的。让我们来看看：

app\code\Sugarcode\Test\Model\Total\Fee.php

<?php
/**
 * Copyright © 2015 Magento. All rights reserved.
 * See COPYING.txt for license details.
 */
namespace Sugarcode\Test\Model\Total;


class Fee extends \Magento\Quote\Model\Quote\Address\Total\AbstractTotal
{
   /**
     * Collect grand total address amount
     *
     * @param \Magento\Quote\Model\Quote $quote
     * @param \Magento\Quote\Api\Data\ShippingAssignmentInterface $shippingAssignment
     * @param \Magento\Quote\Model\Quote\Address\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,
        \Magento\Quote\Api\Data\ShippingAssignmentInterface $shippingAssignment,
        \Magento\Quote\Model\Quote\Address\Total $total
    ) {
        parent::collect($quote, $shippingAssignment, $total);


        $exist_amount = 0; //$quote->getFee(); 
        // $fee = 100; //Excellence_Fee_Model_Fee::getFee();
        // TAKE A LOOK AT THIS:
        $fee = getFeeFromExternalAPI()

        // I successfully get the FEE but how to update the value of checkbox in the UI???

        $balance = $fee - $exist_amount;
        
        $total->setTotalAmount('fee', $balance);
        $total->setBaseTotalAmount('fee', $balance);

        $total->setFee($balance);
        $total->setBaseFee($balance);

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


        return $this;
    } 

    protected function clearValues(Address\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);
    }
    /**
     * @param \Magento\Quote\Model\Quote $quote
     * @param Address\Total $total
     * @return array|null
     */
    /**
     * Assign subtotal amount and label to address object
     *
     * @param \Magento\Quote\Model\Quote $quote
     * @param Address\Total $total
     * @return array
     * @SuppressWarnings(PHPMD.UnusedFormalParameter)
     */
    public function fetch(\Magento\Quote\Model\Quote $quote, \Magento\Quote\Model\Quote\Address\Total $total)
    {
        return [
            'code' => 'fee',
            'title' => 'Fee',
            'value' => 100
        ];
    }

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