致命错误：未捕获的错误：在 null 上调用成员函数 dispatch()答案

【问题标题】：Fatal error: Uncaught Error: Call to a member function dispatch() on null致命错误：未捕获的错误：在 null 上调用成员函数 dispatch()
【发布时间】：2020-02-16 14:36:28
【问题描述】：

完整代码的链接。 Download from here

我正在学习 Magento 2，现在遇到了一个错误。这是调用我的前端视图块时的错误消息。

Fatal error: Uncaught Error: Call to a member function dispatch() on null in C:\wamp64\www\magento2\vendor\magento\framework\Model\ResourceModel\Db\Collection\AbstractCollection.php:541 Stack trace: #0 C:\wamp64\www\magento2\vendor\magento\framework\Data\Collection\AbstractDb.php(577): Magento\Framework\Model\ResourceModel\Db\Collection\AbstractCollection->_beforeLoad() #1 C:\wamp64\www\magento2\vendor\magento\framework\Data\Collection\AbstractDb.php(565): Magento\Framework\Data\Collection\AbstractDb->loadWithFilter(false, false) #2 C:\wamp64\www\magento2\vendor\magento\framework\Data\Collection.php(333): Magento\Framework\Data\Collection\AbstractDb->load() #3 C:\wamp64\www\magento2\app\code\Mastering\SampleModule\Block\Hello.php(19): Magento\Framework\Data\Collection->getItems() #4 C:\wamp64\www\magento2\app\code\Mastering\SampleModule\view\frontend\templates\hello.phtml(7): Mastering\SampleModule\Block\Hello->getItems() #5 C:\wamp64\www\magento2\vendor\magento\framework\View\TemplateEngine\Php.php(59): include('C:\\wamp in C:\wamp64\www\magento2\vendor\magento\framework\Model\ResourceModel\Db\Collection\AbstractCollection.php on line 541

这是我卡在 Hello.php 类中的代码。

<?php

namespace Mastering\SampleModule\Block;

use Magento\Framework\View\Element\Template;
use Mastering\SampleModule\Model\ResourceModel\Item\CollectionFactory;
class Hello extends Template {

    private $collectionFactory;

    public function __construct(Template\Context $context, CollectionFactory $collectionFactory, array $data = [] ){
        $this->collectionFactory = $collectionFactory;
        parent::__construct($context, $data);
    }

    public function getItems() {
        return $this->collectionFactory->create()->getItems();
    }

}

Collection.php 类

namespace Mastering\SampleModule\Model\ResourceModel\Item;

use Magento\Framework\Model\ResourceModel\Db\Collection\AbstractCollection;
use Mastering\SampleModule\Model\Item;
use Mastering\SampleModule\Model\ResourceModel\Item as ItemResource;

class Collection extends AbstractCollection {

    protected $_idFieldName = 'id';

    public function __construct() {
        $this->_init( Item::class, ItemResource::class );

    }
}

app\code\Mastering\SampleModule\view\frontend\layout\mastering_index_index.xml

<?xml version="1.0"?>
<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" layout="1column" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
    <body>
        <referenceContainer name="content">
            <block name="mastering_hello" class="Mastering\SampleModule\Block\Hello" template="hello.phtml" />
        </referenceContainer>
    </body>
</page>

Hello.phtml 查看文件

<?php
/** @var \Mastering\SampleModule\Block\Hello $block */

//var_dump($block->getItems());
?>

<?php foreach($block->getItems() as $item ): ?>
    <p>
        <?php echo $item->getName(); ?>: <?php $item->getDescription(); ?>
    </p>
<?php endforeach; ?>

【问题讨论】：

我也面临类似的问题。

标签： php magento2

【解决方案1】：

在你的 Collection.php 类中，尝试用一个 _ 而不是两个 __ 编写构造函数，你的代码会是这样的：

public function _construct() {
    $this->_init( Item::class, ItemResource::class );

}

【讨论】：