WooCommerce购物车图标切换代码报错求助：get_cart()调用空对象

问题背景 #

几年前在WordPress站点添加代码，实现商品加入购物车后将购物车图标切换为勾选图标，当时运行正常。近期站点出现严重错误，经排查定位到该代码，怀疑是WooCommerce版本更新引发的问题。

错误信息 #

Fatal error: Uncaught Error: Call to a member function get_cart() on null in /home/modjargo/public_html/wp-content/themes/ModjajiBooks/functions.php:159 Stack trace: #0 /home/modjargo/public_html/wp-content/themes/ModjajiBooks/functions.php(169): change_button_text(237520, '') #1 /home/modjargo/public_html/wp-includes/class-wp-hook.php(307): change_ajax_add_to_cart_button_text('', Object(WC_Product_Simple)) #2 /home/modjargo/public_html/wp-includes/plugin.php(191): WP_Hook->apply_filters('', Array) #3 /home/modjargo/public_html/wp-content/plugins/woocommerce/includes/class-wc-product-simple.php(62): apply_filters('woocommerce_pro...', 'Add to basket', Object(WC_Product_Simple)) #4 /home/modjargo/public_html/wp-content/plugins/woocommerce/templates/loop/add-to-cart.php(32): WC_Product_Simple->add_to_cart_text() #5 /home/modjargo/public_html/wp-content/plugins/woocommerce/includes/wc-core-functions.php(345): include('/home/modjargo/...') #6 /home/modjargo/public_html/wp-content/plugins/woocommerce/in in /home/modjargo/public_html/wp-content/themes/ModjajiBooks/functions.php on line 159
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报错代码 #

function change_button_text( $product_id, $button_text ) {
    foreach( WC()->cart->get_cart() as $item ) {
        if( $product_id === $item['product_id'] ) {
            return __('N', 'woocommerce');
        }
    }
    return $button_text;
}
add_filter( 'woocommerce_product_add_to_cart_text', 'change_ajax_add_to_cart_button_text', 10, 2 );
function change_ajax_add_to_cart_button_text( $button_text, $product ) {
    if ( $product->is_type('simple') ) {
        $button_text = change_button_text( $product->get_id(), $button_text );
    }
    return $button_text;
}

问题根源 #

错误核心是WC()->cart返回了null，直接调用get_cart()触发致命错误。在WooCommerce新版本中：

• WC()->cart并非在所有场景下都能初始化，比如页面加载早期、后台预览、静态生成等非活跃用户会话场景
• 原代码未做任何前置判断，强行调用购物车对象的方法，导致报错

修复代码 #

修改change_button_text函数，先验证购物车对象的可用性：

function change_button_text( $product_id, $button_text ) {
    // 先检查购物车对象是否存在且具备get_cart方法
    if ( ! WC()->cart || ! method_exists( WC()->cart, 'get_cart' ) ) {
        return $button_text;
    }
    
    foreach( WC()->cart->get_cart() as $item ) {
        if( $product_id === $item['product_id'] ) {
            return __('N', 'woocommerce');
        }
    }
    return $button_text;
}
add_filter( 'woocommerce_product_add_to_cart_text', 'change_ajax_add_to_cart_button_text', 10, 2 );
function change_ajax_add_to_cart_button_text( $button_text, $product ) {
    if ( $product->is_type('simple') ) {
        $button_text = change_button_text( $product->get_id(), $button_text );
    }
    return $button_text;
}

优化建议 #

• 若站点仅允许登录用户购物，可增加is_user_logged_in()判断，进一步缩小逻辑执行范围
• 考虑改用woocommerce_cart_item_added钩子来标记已加入购物车的商品，避免每次渲染按钮都遍历购物车，提升页面性能

内容的提问来源于stack exchange，提问作者RexTheRunt