Magento2 how to getRequest

If you are trying this from a controller that extends Magento\Framework\App\Action\Action you can get the request with $this->getRequest()->getPost().
If you are in a custom class, you need to inject the request in the constructor.

<?php
namespace Namespace\Module\Something;
class ClassName 
{
    protected $request;
    public function __construct(
       \Magento\Framework\App\RequestInterface $request
        ....//rest of parameters here
    ) {
       $this->request = $request;
       ...//rest of constructor here
    }
    public function getPost()
    {
        return $this->request->getPostValue();//in Magento 2.*
    }
}

Hi you can get it easily in models, blocks and controllers by using:

$this->getRequest()->getPost() 

Or add Magento\Framework\App\RequestInterface to the constructor parameters in your own classes:

<?php
namespace MyModuleNameSpace\MyModule\Block
use Magento\Framework\App\RequestInterface;

class MyClass
{
    /**
     * Request instance
     *
     * @var \Magento\Framework\App\RequestInterface
     */
    protected $request;

    /**
     * @param RequestInterface $request
     */
    public function __construct(RequestInterface $request)
    {
        $this->request = $request;
    }

    public function getMyPostParams()
    {
        $postData = $this->request->getPost();
    }
}

This should work, just test it. Compare and see what is missing.

<?php
namespace MyModuleNameSpace\MyModule\Block
use Magento\Framework\App\RequestInterface;

class MyClass extends \Magento\Framework\View\Element\Template
{
    /**
     * Request instance
     *
     * @var \Magento\Framework\App\RequestInterface
     */
    protected $request;

    /**
     * @param RequestInterface $request
     */
    public function __construct(
        RequestInterface $request,
        \Magento\Framework\View\Element\Template\Context $context,
        array $data = [])
    {
        $this->request = $request;
        parent::__construct($context, $data);
    }

    public function getMyPostParams()
    {
        $postData = $this->request->getPost();
    }
}