如何在 WooCommerce Checkout 中实施基于单选按钮选择的动态费用？

<code class="php">add_action( 'woocommerce_form_field_radio', 'custom_form_field_radio', 20, 4 );
function custom_form_field_radio( $field, $key, $args, $value ) {
    if ( ! empty( $args['options'] ) &amp;&amp; is_checkout() ) {
        $field = str_replace( '</label><input ', '</label><br><input ', $field );
        $field = str_replace( '<label ', '<label style="display:inline;margin-left:8px;" ', $field );
    }
    return $field;
}

<code class="php">add_action( 'woocommerce_cart_calculate_fees', 'add_packaging_fee', 20, 1 );
function add_packaging_fee( $cart ) {
    if ( is_admin() &amp;&amp; ! defined( 'DOING_AJAX' ) )
        return;

    $packing_fee = WC()->session->get( 'chosen_packing' ); // Dynamic packing fee
    $fee = $packing_fee === 'box' ? 9.00 : 3.00;
    $cart->add_fee( __( 'Packaging fee', 'woocommerce' ), $fee );
}</code>

<code class="php">add_action( 'woocommerce_review_order_after_shipping', 'checkout_shipping_form_packing_addition', 20 );
function checkout_shipping_form_packing_addition() {
    $domain = 'woocommerce';

    echo '<tr class="packing-select"><th>' . __('Packing options', $domain) . '</th><td>';

    $chosen   = WC()->session->get('chosen_packing');
    $chosen   = empty($chosen) ? WC()->checkout->get_value('radio_packing') : $chosen;
    $chosen   = empty($chosen) ? 'bag' : $chosen;

    // Add a custom checkbox field
    woocommerce_form_field( 'radio_packing', array(
        'type' => 'radio',
        'class' => array( 'form-row-wide packing' ),
        'options' => array(
            'bag' => __('In a bag '.wc_price(3.00), $domain),
            'box' => __('In a gift box '.wc_price(9.00), $domain),
        ),
        'default' => $chosen,
    ), $chosen );

    echo '</td></tr>';
}</code>

<code class="php">add_action( 'wp_footer', 'checkout_shipping_packing_script' );
function checkout_shipping_packing_script() {
    if ( ! is_checkout() )
        return; // Only checkout page
    ?>
    <script type="text/javascript">
    jQuery( function($){
        $('form.checkout').on('change', 'input[name=radio_packing]', function(e){
            e.preventDefault();
            var p = $(this).val();
            $.ajax({
                type: 'POST',
                url: wc_checkout_params.ajax_url,
                data: {
                    'action': 'woo_get_ajax_data',
                    'packing': p,
                },
                success: function (result) {
                    $('body').trigger('update_checkout');
                    console.log('response: '+result); // just for testing | TO BE REMOVED
                },
                error: function(error){
                    console.log(error); // just for testing | TO BE REMOVED
                }
            });
        });
    });
    </script>
    <?php

}

<code class="php">add_action( 'wp_ajax_woo_get_ajax_data', 'woo_get_ajax_data' );
add_action( 'wp_ajax_nopriv_woo_get_ajax_data', 'woo_get_ajax_data' );
function woo_get_ajax_data() {
    if ( isset($_POST['packing']) ){
        $packing = sanitize_key( $_POST['packing'] );
        WC()->session->set('chosen_packing', $packing );
        echo json_encode( $packing );
    }
    die(); // Alway at the end (to avoid server error 500)
}</code>