Php 使用会话将项目添加到购物篮

这是一个购物篮，用户可以单击addtobasket传递action=add变量，这是从switch语句中选择的。但是，第一次添加项目时会导致错误（底部）。这只是第一次发生，这让我相信这是因为会话[cart]尚未创建

变量设置如下：

if(isset($_GET['id'])) 
{
$Item_ID = $_GET['id'];//the product id from the URL 
$action = $_GET['action'];//the action from the URL 
} 
else
{
$action = "nothing";
}




<?php

if(empty($_SESSION['User_loggedin']))
{ 
header ('Location: logon.php');
}
else
{

switch($action) { //decide what to do 

    case "add":
        $_SESSION['cart'][$Item_ID]++; //add one to the quantity of the product with id $product_id 
    break;

    case "remove":
        $_SESSION['cart'][$Item_ID]--; //remove one from the quantity of the product with id $product_id 
        if($_SESSION['cart'][$Item_ID] == 0) unset($_SESSION['cart'][$Item_ID]); //if the quantity is zero, remove it completely (using the 'unset' function) - otherwise is will show zero, then -1, -2 etc when the user keeps removing items. 
    break;

    case "empty":
        unset($_SESSION['cart']); //unset the whole cart, i.e. empty the cart. 
    break;

    case "nothing":
    break;
}

if(empty($_SESSION['cart']))
{ 
echo "You have no items in your shopping cart.";
}

---

这是因为没有为第一个请求初始化$\u会话['cart']变量。试试下面的方法

if(empty($_SESSION['User_loggedin']))
{ 
header ('Location: logon.php');
}
else
{

   // Added this...
   if(empty($_SESSION['cart'])){
       $_SESSION['cart'] = array();
   }

switch($action) { //decide what to do 

    case "add":
        $_SESSION['cart'][$Item_ID]++; //add one to the quantity of the product with id $product_id 
    break;

    case "remove":
        $_SESSION['cart'][$Item_ID]--; //remove one from the quantity of the product with id $product_id 
        if($_SESSION['cart'][$Item_ID] == 0) unset($_SESSION['cart'][$Item_ID]); //if the quantity is zero, remove it completely (using the 'unset' function) - otherwise is will show zero, then -1, -2 etc when the user keeps removing items. 
    break;

    case "empty":
        unset($_SESSION['cart']); //unset the whole cart, i.e. empty the cart. 
    break;

    case "nothing":
    break;
}

if(empty($_SESSION['cart']))
{ 
echo "You have no items in your shopping cart.";
}

---

如果您认为尚未创建$\u SESSION['cart']变量，只需通过

if (!isset($_SESSION['cart']))
{
    //Initialize variable
}

---

此伪代码将检查变量是否未设置，然后执行一些后续代码
（例如

$\u SESSION['cart']=array（）；

）。

到目前为止没有找到答案：/

if (!isset($_SESSION['cart']))
{
    //Initialize variable
}