我有3个单独的文件，item.php，proposal.php和output.php-这应该是一个购物车一样的应用程序，其想法是为用户选择一个项目和项目的Proposal类...但是我遇到了以下错误：

**致命错误：Uncaught Error：**Cannot use object of type __PHP_Incomplete_Class as array in C：\xampp\htdocs\proposal.php：12堆栈跟踪：#0 C：\xampp\htdocs\output.php（9）：Proposal->addItem（Object（Item））#1 {main} thrown in C：\xampp\htdocs\proposal.php on line 12

我已经在SO & Google上搜索过了，尝试了各种方法，包括将session_start()放在item.php和proposal.php的包含之前，但是这并没有解决这个问题，错误只是变成了：
不能将Proposal类型的对象用作数组
运行PHP 7.0.9

item.php

<?php

    class Item {
        protected $id;
        protected $name;
        protected $manufacturer;
        protected $model;
        protected $qty;
        protected $serial;

        public function __construct($id,$name,$manufacturer,$model,$qty,$serial) {
            $this->id = $id;
            $this->name = $name;
            $this->manufacturer = $manufacturer;
            $this->model = $model;
            $this->qty = $qty;
            $this->serial = $serial;
        }

        public function getId() {
            return $this->id;
        }

        public function getName() {
            return $this->name;
        }

        public function getManufacturer() {
            return $this->manufacturer;
        }

        public function getModel() {
            return $this->model;
        }

        public function getQty() {
            return $this->qty;
        }

        public function getSerial() {
            return $this->serial;
        }                                
    }

字符串

提案.php

class Proposal {
        protected $items = array();

        public function __construct() {
            $this->items = isset($_SESSION['proposal']) ? $_SESSION['proposal'] : array();
        }

        public function addItem(Item $item) {
            $id = $item->getId();
            // the following line is line 12 of proposal.php
            if(isset($this->items[$id])) {
                $this->items[$id]['qty'] = $this->items[$id]['qty'] + $item->getQty();
            }
            else {
                $this->items[$id] = $item;
            }
        }
    }

型

output.php

session_start();
    include('item.php');
    include('proposal.php');

    $item = new Item($_GET['id'],$_GET['name'],$_GET['manufacturer'],$_GET['model'],$_GET['qty'],$_GET['serial']);
    $proposal = new Proposal();

    $proposal->addItem($item);

    $_SESSION['proposal'] = $proposal;

    // view output in array/object format if session variable set
    if(isset($_SESSION['proposal'])) { print '<pre>' . print_r($_SESSION['proposal'],1) . '</pre>'; }

型

**编辑：**我相信这个问题可能与会话有关，因为错误直到第二次运行才出现。

第一次运行的输出为：

Proposal Object
(
    [items:protected] => Array
        (
            [25] => Item Object
                (
                    [id:protected] => 25
                    [name:protected] => Computer
                    [manufacturer:protected] => Dell
                    [model:protected] => Alienware
                    [qty:protected] => 11
                    [serial:protected] => 12345678
                )

        )

)

型