Contact Post Controller overridden in Custom Module not working

Question

I have override contact form post controller in custom module. It is calling from my module but i am getting error as

Fatal error: Uncaught Error: Call to a member function send()

private function sendEmail($post) {
    $this->mail->send($post['email'], ['data' => new \Magento\Framework\DataObject($post)]);
}

print_r($post);

$post is giving data

Vendor/Module/etc/frontend/di.xml

<?xml version="1.0"?>
    <config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <preference for="Magento\Contact\Controller\Index\Post" type="Vendor\Module\Controller\Index\Post" />
</config>

Vendor/Module/Controller/Post.php

<?php

namespace Vendor\Module\Controller\Index;

use Magento\Contact\Model\ConfigInterface;
use Magento\Contact\Model\MailInterface;
use Magento\Framework\App\Action\Context;
use Magento\Framework\App\ObjectManager;
use Magento\Framework\App\Request\DataPersistorInterface;
use Magento\Framework\Controller\Result\Redirect;
use Magento\Framework\Exception\LocalizedException;
use Magento\Framework\HTTP\PhpEnvironment\Request;
use Psr\Log\LoggerInterface;

class Post extends \Magento\Contact\Controller\Index {

private static $_siteVerifyUrl = "https://www.google.com/recaptcha/api/siteverify?";
private $_secret;
private static $_version = "php_1.0";

/**
 * @var DataPersistorInterface
 */
private $dataPersistor;

/**
 * @var Context
 */
private $context;

/**
 * @var MailInterface
 */
private $mail;

/**
 * @var LoggerInterface
 */
private $logger;

/**
 * @param Context $context
 * @param ConfigInterface $contactsConfig
 * @param MailInterface $mail
 * @param DataPersistorInterface $dataPersistor
 * @param LoggerInterface $logger
 */

/**
 * Post user question
 *
 * @return Redirect
 */
public function execute() {


    if (!$this->isPostRequest()) {
        return $this->resultRedirectFactory->create()->setPath('*/*/');
    }
    try {
        echo '<pre>';
        print_r($this->getRequest()->getPostValue());
        echo '</pre>';

        echo '<pre>';
        print_r($this->validatedParams());
        echo '</pre>';


        $captcha = $this->getRequest()->getParam('g-recaptcha-response');
        $secret = '6LfTaGIUAAAAANO90oUqqLs3oNt-qy6_9g2_eC5R';
        $response = null;
        $path = self::$_siteVerifyUrl;
        $dataC = array(
            'secret' => $secret,
            'remoteip' => $_SERVER["REMOTE_ADDR"],
            'v' => self::$_version,
            'response' => $captcha
        );
        $req = "";
        foreach ($dataC as $key => $value) {
            $req .= $key . '=' . urlencode(stripslashes($value)) . '&';
        }
        $req = substr($req, 0, strlen($req) - 1);
        $response = file_get_contents($path . $req);
        $answers = json_decode($response, true);

        if (trim($answers ['success']) == true) {
            $this->sendEmail($this->validatedParams());
            $this->messageManager->addSuccess(
                    __('Thank you for contacting us with your comments and questions. We\'ll respond to you very soon.')
            );
            $this->getDataPersistor()->clear('contact_us');
        } else {
            $this->messageManager->addError(__('Invalid Recaptcha'));
        }
        $this->sendEmail($this->validatedParams());
        $this->messageManager->addSuccess(
                __('Thank you for contacting us with your comments and questions. We\'ll respond to you very soon.')
        );
        $this->getDataPersistor()->clear('contact_us');
    } catch (LocalizedException $e) {
        $this->messageManager->addErrorMessage($e->getMessage());
        $this->getDataPersistor()->set('contact_us', $this->getRequest()->getParams());
    } catch (\Exception $e) {
        $this->logger->critical($e);
        $this->messageManager->addErrorMessage(
                __('An error occurred while processing your form. Please try again later.')
        );
        $this->getDataPersistor()->set('contact_us', $this->getRequest()->getParams());
    }
    return $this->resultRedirectFactory->create()->setPath('contact/index');
}

/**
 * Get Data Persistor
 *
 * @return DataPersistorInterface
 */
private function getDataPersistor() {
    if ($this->dataPersistor === null) {
        $this->dataPersistor = ObjectManager::getInstance()
                ->get(DataPersistorInterface::class);
    }

    return $this->dataPersistor;
}

/**
 * @param array $post Post data from contact form
 * @return void
 */
private function sendEmail($post) {
    print_r($post);
    $this->mail->send($post['email'], ['data' => new \Magento\Framework\DataObject($post)]);
}

/**
 * @return bool
 */
private function isPostRequest() {
    /** @var Request $request */
    $request = $this->getRequest();
    return !empty($request->getPostValue());
}

/**
 * @return array
 * @throws \Exception
 */
private function validatedParams() {
    $request = $this->getRequest();
    if (trim($request->getParam('name')) === '') {
        throw new LocalizedException(__('Name is missing'));
    }
    if (trim($request->getParam('comment')) === '') {
        throw new LocalizedException(__('Comment is missing'));
    }
    if (false === \strpos($request->getParam('email'), '@')) {
        throw new LocalizedException(__('Invalid email address'));
    }
    if (trim($request->getParam('hideit')) !== '') {
        throw new \Exception();
    }

    return $request->getParams();
}

}

Answer 1

First, change the line:

class Post extends \Magento\Contact\Controller\Index

to

class Post extends \Magento\Contact\Controller\Post

If still, the problem exists, please post the outcome.

Update: Please put the __construct() in the class:

public function __construct(
    Context $context,
    ConfigInterface $contactsConfig,
    MailInterface $mail,
    DataPersistorInterface $dataPersistor,
    LoggerInterface $logger = null
) {
       parent::__construct($context, $contactsConfig);
       $this->context = $context;
       $this->mail = $mail;
       $this->dataPersistor = $dataPersistor;
       $this->logger = $logger ?: ObjectManager::getInstance()->get(LoggerInterface::class);
   }

In the __construct(), we have used object of Magento\Contact\Model\MailInterface class and initialized $this->mail with this object.

I hope it should solve your problem.