PHP购物车问题：添加到购物车按钮跳转后商品未显示在表格

你遇到的页面空白+购物车商品不显示问题，主要是PHP大小写错误、会话未初始化、HTML/JS语法错误这几个核心问题导致的，下面逐一拆解并给出完整修复方案：

核心错误点 #

• 会话未启动：使用$_SESSION存储购物车数据前，必须调用session_start()初始化会话，否则无法读写会话数据
• PHP超级全局变量大小写错误：$_post、$_get是错误写法，PHP中这些变量严格区分大小写，正确写法为$_POST、$_GET
• SESSION数组键名不统一：代码里混用了shopping_cart和shopping_Cart，导致无法正确判断商品是否已存在于购物车
• HTML/JS语法漏洞：
  • img标签未闭合，缺少/>
  • CSS里bacgkround-color拼写错误、border:1px solid未指定颜色
  • 删除按钮的a标签未闭合，缺少闭合>
  • JS跳转代码存在语法错误（缺少引号和闭合标签）
  • 表格里coslpan是拼写错误，正确为colspan

修正后的完整代码 #

<?php
// 必须先初始化会话，放在所有输出之前
session_start();
require "includes/dbh.php";

if(isset($_POST['add'])){
    if(isset($_SESSION['shopping_cart'])){
        // 统一SESSION数组键名，避免大小写问题
        $item_array_id = array_column($_SESSION['shopping_cart'],'item_id');
        if(!in_array($_GET['id'], $item_array_id)){
            $count = count($_SESSION['shopping_cart']);
            $item_array = array(
                'item_id' => $_GET['id'],
                'item_name' => $_POST['hidden_name'],
                'item_price' => $_POST['hidden_price'],
                'item_quantity' => $_POST['quantity'],
            );
            $_SESSION['shopping_cart'][$count] = $item_array;
        }else{
            echo "<script>alert('Item already added');</script>";
            echo "<script>window.location='displayitems.php';</script>";
        }
    }else{
        $item_array = array(
            'item_id' => $_GET['id'],
            'item_name' => $_POST['hidden_name'],
            'item_price' => $_POST['hidden_price'],
            'item_quantity' => $_POST['quantity'],
        );
        $_SESSION['shopping_cart'][0] = $item_array;
    }
}

if(isset($_GET['action'])){
    if($_GET['action']=='delete'){
        // 先判断购物车是否存在，避免报错
        if(isset($_SESSION['shopping_cart'])){
            foreach($_SESSION['shopping_cart'] as $keys => $values){
                if($values['item_id'] == $_GET['id']){
                    unset($_SESSION['shopping_cart'][$keys]);
                    echo '<script>alert("Item removed");</script>';
                    echo '<script>window.location="displayitems.php";</script>';
                }
            }
        }
    }
}
?>
<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <title>Page Title</title>
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <link rel="stylesheet" type="text/css" media="screen" href="main.css" />
    <script src="main.js"></script>
    <style>
        .product{
            border:1px solid #ccc; /* 补充边框颜色 */
            margin:-1px 19px 3px -1px;
            padding: 10px;
            text-align:center;
            background-color:#efefef; /* 修正拼写错误 */
        }
    </style>
</head>
<body>
<?php
if(isset($_SESSION['userId'])){
    echo '<div id="items" >';
    include_once 'includes/dbh.php';
    require 'includes/gallery-upload.in.php';
    $sql="SELECT * FROM gallery ORDER BY orderitems DESC;";
    $stmt=mysqli_stmt_init($conn);
    if(!mysqli_stmt_prepare($stmt,$sql)){
        echo "SQL statement failed in displayitems.php";
    }else{
        mysqli_stmt_execute($stmt);
        $result=mysqli_stmt_get_result($stmt);
        while($row=mysqli_fetch_assoc($result)) {
?>
<!-- 添加到购物车按钮的表单 -->
<div class="col-md-3">
    <form method="POST" action="displayitems.php?action=add&id=<?php echo $row["idGallery"]?>">
        <div class="product">
            <!-- 闭合img标签 -->
            <img src="images/<?php echo $row['imgFullNameGallery'] ?>" />
            <br>
            <h3><?php echo $row['nameitem']?></h3>
            <h3><?php echo $row['price']?></h3>
            <!-- 增加min属性防止输入负数 -->
            <input type='number' name='quantity' value="1" min="1">
            <input type='hidden' name='hidden_name' value="<?php echo $row['nameitem']?>">
            <input type='hidden' name='hidden_price' value="<?php echo $row['price']?>">
            <button type='submit' name='add'>Add to cart</button>
        </div>
    </form>
</div>
<?php
        }
    }
}
?>
<div style="clear:both"></div> <!-- 修正冒号位置 -->
<h3 class="title2">Shopping cart details</h3>
<div class="table table-bordered">
    <table>
        <tr>
            <th width="40%">Item Name</th>
            <th width="10%">Quantity</th>
            <th width="20%">Price</th>
            <th width="15%">Total</th>
            <th width="5%">Action</th>
        </tr>
        <?php
        if(!empty($_SESSION['shopping_cart'])){
            $total=0;
            foreach($_SESSION['shopping_cart'] as $keys => $values){
        ?>
        <tr>
            <td><?php echo $values['item_name'];?></td>
            <td><?php echo $values['item_quantity'];?></td>
            <td>$<?php echo $values['item_price'];?></td>
            <td><?php echo number_format($values['item_quantity']*$values['item_price'],2);?></td>
            <!-- 修复a标签闭合问题 -->
            <td><a href="displayitems.php?action=delete&id=<?php echo $values['item_id']; ?>" class="text-danger">REMOVE</a></td>
        </tr>
        <?php
                $total += ($values['item_quantity']*$values['item_price']);
            }
        ?>
        <tr>
            <!-- 修复colspan拼写错误 -->
            <td colspan="3" align="right">Total</td>
            <td align="right">$<?php echo number_format($total,2);?></td>
            <td></td> <!-- 补充空单元格对齐 -->
        </tr>
        <?php
        } else {
            // 购物车为空时增加提示
            echo '<tr><td colspan="5" align="center">Your shopping cart is empty</td></tr>';
        }
        ?>
    </table>
</div>
</body>
</html>

额外优化建议 #

• 对用户输入的quantity进行合法性校验（比如是否为正整数）
• 建议使用预处理语句处理$_GET['id']，避免SQL注入风险
• 可以添加购物车商品数量的实时更新提示，提升用户体验

内容的提问来源于stack exchange，提问作者Jenel Hapitana