Magento 2 get order in custom block - magento2

Question

I have a custom module which sends email to custom email address after successful purchase. It works well but now I need to get gift message from order.
Here is my Block code
<?php
namespace Test\Test2\Block\Vendor\Shipment;
class Items extends \Magento\Framework\View\Element\Template
{
const DEFAULT_TYPE = 'default';
public function getItemRenderer($type)
{
/** #var \Magento\Framework\View\Element\RendererList $rendererList */
$rendererList = $this->getRendererListName() ? $this->getLayout()->getBlock($this->getRendererListName()) : $this->getChildBlock('renderer.list');
if (!$rendererList) {
throw new \RuntimeException('Renderer list for block "' . $this->getNameInLayout() . '" is not defined');
}
$overriddenTemplates = $this->getOverriddenTemplates() ?: [];
$template = isset($overriddenTemplates[$type]) ? $overriddenTemplates[$type] : $this->getRendererTemplate();
$renderer = $rendererList->getRenderer($type, self::DEFAULT_TYPE, $template);
$renderer->setRenderedBlock($this);
return $renderer;
}
public function getItemHtml(\Magento\Framework\DataObject $item)
{
$block = $this->getItemRenderer($item->getProductType())->setItem($item);
return $block->toHtml();
}
}
and email template .phtml
<?php $_items = $block->getItems() ?>
<?php $_order = $block->getOrder() ?>
<?php if ($_items): ?>
<table class="items email-items shipment-items order-items">
<thead>
<tr>
<th class="item-info">
<?= /* #escapeNotVerified */ __('Items'); ?>
</th>
<th class="item-price">
<?= /* #escapeNotVerified */ __('Price'); ?>
</th>
<th class="item-qty">
<?= /* #escapeNotVerified */ __('Qty'); ?>
</th>
<th class="row-total">
<?= /* #escapeNotVerified */ __('Total'); ?>
</th>
</tr>
</thead>
<?php foreach ($_items as $_item): ?>
<?php
if ($_item->getParentItem()) {
continue;
}
?>
<tbody>
<?= $block->getItemHtml($_item) ?>
</tbody>
<?php endforeach; ?>
</table>
<?php $_giftMessage = $this->helper('Magento\GiftMessage\Helper\Message')->getGiftMessage($_order->getGiftMessageId()); ?>
<?php if ($_giftMessage): ?>
<br />
<table class="message-gift">
<tr>
<td>
<h3><?= /* #escapeNotVerified */ __('Gift Message for this Order') ?></h3>
<strong><?= /* #escapeNotVerified */ __('From:') ?></strong> <?= $block->escapeHtml($_giftMessage->getSender()) ?>
<br /><strong><?= /* #escapeNotVerified */ __('To:') ?></strong> <?= $block->escapeHtml($_giftMessage->getRecipient()) ?>
<br /><strong><?= /* #escapeNotVerified */ __('Message:') ?></strong>
<br /><?= $block->escapeHtml($_giftMessage->getMessage()) ?>
</td>
</tr>
</table>
<?php endif; ?>
<?php endif; ?>
Obviously, I receive this error message:
Uncaught Error: Call to a member function getGiftMessageId()
since my block does not have the method getOrder.
But if I try to copy getOrder method from Magento\Sales\Block\Order\Items:
/**
* Retrieve current order model instance
*
* #return \Magento\Sales\Model\Order
*/
public function getOrder()
{
return $this->_coreRegistry->registry('current_order');
}
with __construct part
/**
* #param \Magento\Framework\View\Element\Template\Context $context
* #param \Magento\Framework\Registry $registry
* #param array $data
* #param \Magento\Sales\Model\ResourceModel\Order\Item\CollectionFactory|null $itemCollectionFactory
*/
public function __construct(
\Magento\Framework\View\Element\Template\Context $context,
\Magento\Framework\Registry $registry,
array $data = [],
\Magento\Sales\Model\ResourceModel\Order\Item\CollectionFactory $itemCollectionFactory = null
) {
$this->_coreRegistry = $registry;
$this->itemCollectionFactory = $itemCollectionFactory ?: \Magento\Framework\App\ObjectManager::getInstance()
->get(\Magento\Sales\Model\ResourceModel\Order\Item\CollectionFactory::class);
parent::__construct($context, $data);
}
it still shows an error that order object in null. What am I doing wrong? Or how can I obtain order object in my case? Thanks.