Magento执行InstallData时报Call to a member function dispatch() on null错误

报错Error: Call to a member function dispatch() on null的核心根因是：自定义模型StateMaster重写构造方法时未调用父类AbstractModel的构造方法，导致模型依赖的事件管理器实例为空，执行save操作触发事件分发时调用失败。

以下是具体修复步骤： #

1. 修复Model/StateMaster.php #

补充父类构造所需的依赖并调用父构造，补全后代码如下：

namespace Navien\Custom\Model;
use \Magento\Framework\Model\AbstractModel;
use \Magento\Framework\Model\Context;
use \Magento\Framework\Registry;
use \Psr\Log\LoggerInterface;

class StateMaster extends AbstractModel
{
    protected $_logger;

    public function __construct(
        Context $context,
        Registry $registry,
        LoggerInterface $logger,
        \Magento\Framework\Model\ResourceModel\AbstractResource $resource = null,
        \Magento\Framework\Data\Collection\AbstractDb $resourceCollection = null,
        array $data = []
    ) 
    {
        $this->_logger = $logger;
        // 必须调用父类构造初始化事件管理器等核心依赖
        parent::__construct($context, $registry, $resource, $resourceCollection, $data);
        $this->_init('Navien\Custom\Model\ResourceModel\StateMaster');
    }
}

2. 优化Model/StateData.php（推荐） #

移除不规范的ObjectManager直接调用，改用Magento标准的依赖注入方式，代码可调整为：

namespace Navien\Custom\Model;
use Navien\Custom\Model\StateMasterFactory;
use Navien\Custom\Model\ResourceModel\StateMaster\CollectionFactory;
use Psr\Log\LoggerInterface;

class StateData
{
    protected $_logger;
    protected $_stateMasterFactory;
    protected $_stateCollectionFactory;

    public function __construct(
        LoggerInterface $logger,
        StateMasterFactory $stateMasterFactory,
        CollectionFactory $stateCollectionFactory
    ) 
    {
        $this->_logger = $logger;
        $this->_stateMasterFactory = $stateMasterFactory;
        $this->_stateCollectionFactory = $stateCollectionFactory;
    }

    public function insertStates($states)
    {
        if(empty($states)) return;
        // 直接查询已存在的州编码，效率更高
        $existingCodes = $this->_stateCollectionFactory->create()->getColumnValues('code');
        foreach($states as $state)
        {
            if(!in_array($state['code'], $existingCodes)) {
                $stateMaster = $this->_stateMasterFactory->create();
                $stateMaster->setData($state)->save();
            }
        }
    }
}

3. 简化Collection.php（可选，无特殊需求时可操作） #

移除不必要的依赖注入，保留默认逻辑即可：

namespace Navien\Custom\Model\ResourceModel\StateMaster;

class Collection extends \Magento\Framework\Model\ResourceModel\Db\Collection\AbstractCollection
{
    protected function _construct()
    {
        $this->_init('Navien\Custom\Model\StateMaster','Navien\Custom\Model\ResourceModel\StateMaster');
    }
}

验证生效步骤 #

1. 进入数据库删除setup_module表中module字段为Navien_Custom的记录
2. 执行命令php bin/magento setup:upgrade
3. 检查navien_states表是否已成功插入对应州数据

内容的提问来源于stack exchange，提问作者Sanjay Goswami