Creating a admin controller using adminhtml id - magento2

Question

I'm trying to add a controller accessible on admin menu through url:
https://dev.m2t2.com/admin_k1tgag/admin/helloWorld/index/key/0195fab99cc865bb756a77e8fe5ceedb6f8eee97de91d569398d383cef4f0d81/
Generated by the XML code inserted below. But it keeps returning
Invalid security or form key. Please refresh the page.
Router.xml :
<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:App/etc/routes.xsd">
<router id="admin">
<route id="adminhtml">
<module name="Study_Admin" before="Magento_Backend"/>
</route>
</router>
</config>
In menu i inserted:
<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Backend:etc/menu.xsd">
<menu>
<add id="Study_Admin::greetings" title="Greetings" translate="title" module="Study_Admin" parent="Magento_Backend::content" sortOrder="50" dependsOnModule="Study_Admin" resource="Study_Admin::greetings"/>
<add id="Study_Admin::greetings_helloworld" title="Hello World" translate="title" module="Study_Admin" parent="Study_Admin::greetings" sortOrder="10" dependsOnModule="Study_Admin" action="adminhtml/helloWorld" resource="Study_Admin::greetings"/>
</menu>
</config>
But when i access the controller through the menu i have no success. I started debugging and i checked that non-custom controllers extends \Magento\Backend\App\Action class to pass validations inside magento routing core flow. I did the same but i still have no success.
Below my controller class:
<?php
namespace Study\Controller\Adminhtml\HelloWorld;
use Magento\Framework\App\Action\HttpGetActionInterface as HttpGetActionInterface;
use Magento\Framework\View\Result\Page;
use Magento\Framework\View\Result\PageFactory;
use Magento\Backend\App\Action\Context;
use ‌Magento\Framework\App\ActionInterface;
class Index extends \Magento\Backend\App\Action
{
const MENU_Id = "Study_Admin::greetings_helloworld";
protected $resultPageFActory;
public function __construct(Context $context, PageFactory $resultPageFActory)
{
parent::__construct($context);
$this->resultPageFActory = $resultPageFActory;
}
public function execute()
{
$resultPage = $this->resultPageFActory->create();
$resultPage->setActiveMenu(static::MENU_Id);
$resultPage->getConfig()->getTitle()->prepend(__('Hello World'));
return $resultPage;
// TODO: Implement execute() method.
}
}
The file structure is :
Thanx in advance, and take care.

Answer 1

It works... was just my namespace in Controller's class that had an error
'namespace Study\Admin\Controller\Adminhtml\Helloworld;'