Custom tab in admin product page in magento2

Question

I have created custom tab and added template for this tab using this link.

1. app/code/Namespace/Modulename/view/adminhtml/ui_component/product_form.xml

<form xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Ui:etc/ui_configuration.xsd">
    <fieldset name="demotab">
       <argument name="data" xsi:type="array">
           <item name="config" xsi:type="array">
               <item name="label" xsi:type="string" translate="true">Demo Tab</item>
               <item name="collapsible" xsi:type="boolean">true</item>
               <item name="sortOrder" xsi:type="number">100</item>
           </item>
       </argument>
       <container name="fieldname_container" >
           <argument name="data" xsi:type="array">
               <item name="config" xsi:type="array">
                   <item name="sortOrder" xsi:type="number">160</item>
               </item>
           </argument>
           <htmlContent name="html_content_demo">
               <argument name="block" xsi:type="object">Namespace\Modulename\Block\Adminhtml\Catalog\Product\Edit\Tab\Demo</argument>
           </htmlContent>
       </container>
   </fieldset>
</form>

2. app/code/Namespace/Modulename/Block/Adminhtml/Catalog/Product/Edit/Tab/Demo.php

<?php
namespace Namespace\Modulename\Block\Adminhtml\Catalog\Product\Edit\Tab;

use Magento\Backend\Block\Template\Context;
use Magento\Framework\Registry;

class Demo extends \Magento\Framework\View\Element\Template
{
    /**
     * @var string
     */
    protected $_template = 'product/edit/demo.phtml';

    /**
     * Core registry
     *
     * @var Registry
     */
    protected $_coreRegistry = null;

    public function __construct(
        Context $context,
        Registry $registry,
        array $data = []
    )
    {
        $this->_coreRegistry = $registry;
        parent::__construct($context, $data);
    }

    /**
     * Retrieve product
     *
     * @return \Magento\Catalog\Model\Product
     */
    public function getProduct()
    {
        return $this->_coreRegistry->registry('current_product');
    }

}

3. app/code/Namespace/Modulename/view/adminhtml/templates/product/edit/demo.phtml

<?php echo "This is demo tab content."; ?>

But, The template values does not post in product form save action.

How to solve this...

Thanks.

Answer 1

Use below code in phtml file:

<p id="CustomTab" data-form-part="product_form" > 
    <?php echo "This is demo tab content."; ?> 
</p>