使用会话将项目添加到购物篮

Question

This is a shopping basket and a user can click add to basket passing an action=add variable across and this is selected from the switch statement. However the first time you add an item it causes an error (bottom). This only occurs the first time which leads me to believe that it is because the session[cart] has not been created.

The variables are set here:

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.";
}

Adding items is working fine however the first time I add something to an empty basket I get the error below:

Notice: Undefined index: cart in H:\STUDENT\S0190204\GGJ\Basket.php on line 57 Notice: Undefined index: 1 in H:\STUDENT\S0190204\GGJ\Basket.php on line 57

Answer 1

That is because your $_SESSION['cart'] variable isn't initialized for the first request. Try something like below.

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.";
}